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Types of volcanic eruptions

The image correlates types of volcanoes with their respective eruption, highlighting the differences. Credit: ChiaraCingottini, DensityDesign Research Lab

During a volcanic eruption, lava, tephra (ash, lapilli, volcanic bombs and blocks), and various gases are expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.

There are three different meta types of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The last eruptive metatype is the phreatic eruption, which is driven by the superheating of steam via contact with magma; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.

Within these wide-defining eruptive types are several subtypes. The weakest are Hawaiian and submarine, then Strombolian, followed by Vulcanian and Surtseyan. The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions; the strongest eruptions are called “Ultra Plinian.” Subglacial and phreatic eruptions are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index (VEI), an order of magnitude scale ranging from 0 to 8 that often correlates to eruptive types.

Eruption mechanisms

Volcanic eruptions arise through three main mechanisms:

  • Gas release under decompression causing magmatic eruptions
  • Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions
  • Ejection of entrained particles during steam eruptions causing phreatic eruptions

There are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels magma and tephra.Effusive eruptions, meanwhile, are characterized by the outpouring of lava without significant explosive eruption.

Volcanic eruptions vary widely in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are typically not very dangerous. On the other extreme, Plinian eruptions are large, violent, and highly dangerous explosive events. Volcanoes are not bound to one eruptive style, and frequently display many different types, both passive and explosive, even the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either. Some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones, and some of the strongest Surtseyan eruptions develop along fracture zones. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years. But Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was likely triggered by magma that took a nonstop route from the mantle over just a few months.

Magmatic eruptions

Magmatic eruptions produce juvenile clasts during explosive decompression from gas release. They range in intensity from the relatively small lava fountains on Hawaii to catastrophic Ultra Plinian eruption columns more than 30 km (19 mi) high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii.

Hawaiian

Diagram of a Hawaiian eruption. (key: 1. Ash plume 2. Lava fountain 3. Crater 4. Lava lake 5. Fumaroles 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Sill 10. Magma conduit 11. Magma chamber 12. Dike) © Sémhur

Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of very fluid basalt-type lavas with low gaseous content. The volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the large, broad form of a shield volcano. Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around the summit and from fissure vents radiating out of the center.

Hawaiian eruptions often begin as a line of vent eruptions along a fissure vent, a so-called “curtain of fire.” These die down as the lava begins to concentrate at a few of the vents. Central-vent eruptions, meanwhile, often take the form of large lava fountains (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments; however, when the air is especially thick with clasts, they cannot cool off fast enough due to the surrounding heat, and hit the ground still hot, the accumulation of which forms spatter cones. If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived; Pu’u O’o, a cinder cone of Kilauea, has been erupting continuously since 1983. Another Hawaiian volcanic feature is the formation of active lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock; there are currently only 5 such lakes in the world, and the one at Kīlauea’s Kupaianaha vent is one of them.

Strombolian

Diagram of a Strombolian eruption. (key: 1. Ash plume 2. Lapilli 3. Volcanic ash rain 4. Lava fountain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Dike 10. Magma conduit 11. Magma chamber 12. Sill) © Sémhur

Strombolian eruptions are a type of volcanic eruption, named after the volcano Stromboli, which has been erupting continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within the magma. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs. These grow large enough to rise through the lava column. Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop, throwing magma in the air in a way similar to a soap bubble. Because of the high gas pressures associated with the lavas, continued activity is generally in the form of episodic explosive eruptions accompanied by the distinctive loud blasts. During eruptions, these blasts occur as often as every few minutes.

The term “Strombolian” has been used indiscriminately to describe a wide variety of volcanic eruptions, varying from small volcanic blasts to large eruptive columns. In reality, true Strombolian eruptions are characterized by short-lived and explosive eruptions of lavas with intermediate viscosity, often ejected high into the air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basaltic lava, and its end product is mostly scoria. The relative passivity of Strombolian eruptions, and its non-damaging nature to its source vent allow Strombolian eruptions to continue unabated for thousands of years, and also makes it one of the least dangerous eruptive types.

Strombolian eruptions eject volcanic bombs and lapilli fragments that travel in parabolic paths before landing around their source vent. The steady accumulation of small fragments builds cinder cones composed completely of basaltic pyroclasts. This form of accumulation tends to result in well-ordered rings of tephra.

Strombolian eruptions are similar to Hawaiian eruptions, but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive columns, do not produce some volcanic products associated with Hawaiian volcanism (specifically Pele’s tears and Pele’s hair), and produce fewer molten lava flows (although the eruptive material does tend to form small rivulets).

Vulcanian

Diagram of a Vulcanian eruption. (key: 1. Ash plume 2. Lapilli 3. Lava fountain 4. Volcanic ash rain 5. Volcanic bomb 6. Lava flow 7. Layers of lava and ash 8. Stratum 9. Sill 10. Magma conduit 11. Magma chamber 12. Dike) © Sémhur

Vulcanian eruptions are a type of volcanic eruption, named after the volcano Vulcano, which means the word Volcano. It was named so following Giuseppe Mercalli’s observations of its 1888-1890 eruptions. In Vulcanian eruptions, highly viscous magma within the volcano make it difficult for vesiculate gases to escape. Similar to Strombolian eruptions, this leads to the buildup of high gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. However, unlike Strombolian eruptions, ejected lava fragments are not aerodynamic; this is due to the higher viscosity of Vulcanian magma and the greater incorporation of crystalline material broken off from the former cap. They are also more explosive than their Strombolian counterparts, with eruptive columns often reaching between 5 and 10 km (3 and 6 mi) high. Lastly, Vulcanian deposits are andesitic to dacitic rather than basaltic.

Initial Vulcanian activity is characterized by a series of short-lived explosions, lasting a few minutes to a few hours and typified by the ejection of volcanic bombs and blocks. These eruptions wear down the lava dome holding the magma down, and it disintegrates, leading to much more quiet and continuous eruptions. Thus an early sign of future Vulcanian activity is lava dome growth, and its collapse generates an outpouring of pyroclastic material down the volcano’s slope.

Peléan

Diagram of Peléan eruption. (key: 1. Ash plume 2. Volcanic ash rain 3. Lava dome 4. Volcanic bomb 5. Pyroclastic flow 6. Layers of lava and ash 7. Stratum 8. Magma conduit 9. Magma chamber 10. Dike) © Sémhur

Peléan eruptions (or nuée ardente) are a type of volcanic eruption, named after the volcano Mount Pelée in Martinique, the site of a massive Peléan eruption in 1902 that is one of the worst natural disasters in history. In Peléan eruptions, a large amount of gas, dust, ash, and lava fragments are blown out the volcano’s central crater, driven by the collapse of rhyolite, dacite, and andesite lava dome collapses that often create large eruptive columns. An early sign of a coming eruption is the growth of a so-called Peléan or lava spine, a bulge in the volcano’s summit preempting its total collapse. The material collapses upon itself, forming a fast-moving pyroclastic flow (known as a block-and-ash flow) that moves down the side of the mountain at tremendous speeds, often over 150 km (93 mi) per hour. These massive landslides make Peléan eruptions one of the most dangerous in the world, capable of tearing through populated areas and causing massive loss of life. The 1902 eruption of Mount Pelée caused tremendous destruction, killing more than 30,000 people and competely destroying the town of St. Pierre, the worst volcanic event in the 20th century.

Peléan eruptions are characterized most prominently by the incandescent pyroclastic flows that they drive. The mechanics of a Peléan eruption are very similar to that of a Vulcanian eruption, except that in Peléan eruptions the volcano’s structure is able to withstand more pressure, hence the eruption occurs as one large explosion rather than several smaller ones.

Plinian

Diagram of a Plinian eruption. (key: 1. Ash plume 2. Magma conduit 3. Volcanic ash rain 4. Layers of lava and ash 5. Stratum 6. Magma chamber) © Sémhur

Plinian eruptions (or Vesuvian) are a type of volcanic eruption, named for the historical eruption of Mount Vesuvius in 79 of Mount Vesuvius that buried the Roman towns of Pompeii and Herculaneum, and specifically for its chronicler Pliny the Younger. The process powering Plinian eruptions starts in the magma chamber, where dissolved volatile gases are stored in the magma. The gases vesiculate and accumulate as they rise through the magma conduit. These bubbles agglutinate and once they reach a certain size (about 75% of the total volume of the magma conduit) they explode. The narrow confines of the conduit force the gases and associated magma up, forming an eruptive column. Eruption velocity is controlled by the gas contents of the column, and low-strength surface rocks commonly crack under the pressure of the eruption, forming a flared outgoing structure that pushes the gases even faster.

These massive eruptive columns are the distinctive feature of a Plinian eruption, and reach up 2 to 45 km (1 to 28 mi) into the atmosphere. The densest part of the plume, directly above the volcano, is driven internally by gas expansion. As it reaches higher into the air the plume expands and becomes less dense, convection and thermal expansion of volcanic ash drive it even further up into the stratosphere. At the top of the plume, powerful prevailing winds drive the plume in a direction away from the volcano.

Plinian eruptions are similar to both Vulcanian and Strombolian eruptions, except that rather than creating discrete explosive events, Plinian eruptions form sustained eruptive columns. They are also similar to Hawaiian lava fountains in that both eruptive types produce sustained eruption columns maintained by the growth of bubbles that move up at about the same speed as the magma surrounding them.

Phreatomagmatic eruptions

Phreatomagmatic eruptions are eruptions that arise from interactions between water and magma. They are driven from thermal contraction (as opposed to magmatic eruptions, which are driven by thermal expansion) of magma when it comes in contact with water. This temperature difference between the two causes violent water-lava interactions that make up the eruption. The products of phreatomagmatic eruptions are believed to be more regular in shape and finer grained than the products of magmatic eruptions because of the differences in eruptive mechanisms.

There is debate about the exact nature of phreatomagmatic eruptions, and some scientists believe that fuel-coolant reactions may be more critical to the explosive nature than thermal contraction. Fuel coolant reactions may fragment the volcanic material by propagating stress waves, widening cracks and increasing surface area that ultimetly lead to rapid cooling and explosive contraction-driven eruptions.

Surtseyan

Diagram of a Surtseyan eruption. (key: 1. Water vapor cloud 2. Compressed ash 3. Crater 4. Water 5. Layers of lava and ash 6. Stratum 7. Magma conduit 8. Magma chamber 9. Dike) © Sémhur

A Surtseyan eruption (or hydrovolcanic) is a type of volcanic eruption caused by shallow-water interactions between water and lava, named so after its most famous example, the eruption and formation of the island of Surtsey off the coast of Iceland in 1963. Surtseyan eruptions are the “wet” equivalent of ground-based Strombolian eruptions, but because of where they are taking place they are much more explosive. This is because as water is heated by lava, it flashes in steam and expands violently, fragmenting the magma it is in contact with into fine-grained ash. Surtseyan eruptions are the hallmark of shallow-water volcanic oceanic islands, however they are not specifically confined to them. Surtseyan eruptions can happen on land as well, and are caused by rising magma that comes into contact with an aquifer (water-bearing rock formation) at shallow levels under the volcano. The products of Surtseyan eruptions are generally oxidized palagonite basalts (though andesitic eruptions do occur, albeit rarely), and like Strombolian eruptions Surtseyan eruptions are generally continuous or otherwise rhythmic.

Submarine

Diagram of a Submarine eruption. (key: 1. Water vapor cloud 2. Water 3. Stratum 4. Lava flow 5. Magma conduit 6. Magma chamber 7. Dike 8. Pillow lava) © Sémhur

Submarine eruptions are a type of volcanic eruption that occurs underwater. An estimated 75% of the total volcanic eruptive volume is generated by submarine eruptions near mid ocean ridges alone, however because of the problems associated with detecting deep sea volcanics, they remained virtually unknown until advances in the 1990s made it possible to observe them.

Submarine eruptions may produce seamounts which may break the surface to form volcanic islands and island chains.

Submarine volcanism is driven by various processes. Volcanoes near plate boundaries and mid-ocean ridges are built by the decompression melting of mantle rock that rises on an upwelling portion of a convection cell to the crustal surface. Eruptions associated with subducting zones, meanwhile, are driven by subducting plates that add volatiles to the rising plate, lowering its melting point. Each process generates different rock; mid-ocean ridge volcanics are primarily basaltic, whereas subduction flows are mostly calc-alkaline, and more explosive and viscous.

A diagram of a Subglacial eruption. (key: 1. Water vapor cloud 2. Crater lake 3. Ice 4. Layers of lava and ash 5. Stratum 6. Pillow lava 7. Magma conduit 8. Magma chamber 9. Dike) © Sémhur

Subglacial

Subglacial eruptions are a type of volcanic eruption characterized by interactions between lava and ice, often under a glacier. The nature of glaciovolcanism dictates that it occurs at areas of high latitude and high altitude. It has been suggested that subglacial volcanoes that are not actively erupting often dump heat into the ice covering them, producing meltwater. This meltwater mix means that subglacial eruptions often generate dangerous jökulhlaups (floods) and lahars.

The study of glaciovolcanism is still a relatively new field. Early accounts described the unusual flat-topped steep-sided volcanoes (called tuyas) in Iceland that were suggested to have formed from eruptions below ice. The first English-language paper on the subject was published in 1947 by William Henry Mathews, describing the Tuya Butte field in northwest British Columbia, Canada. The eruptive process that builds these structures, originally inferred in the paper, begins with volcanic growth below the glacier. At first the eruptions resemble those that occur in the deep sea, forming piles of pillow lava at the base of the volcanic structure. Some of the lava shatters when it comes in contact with the cold ice, forming a glassy breccia called hyaloclastite. After a while the ice finally melts into a lake, and the more explosive eruptions of Surtseyan activity begins, building up flanks made up of mostly hyaloclastite. Eventually the lake boils off from continued volcanism, and the lava flows become more effusive and thicken as the lava cools much more slowly, often forming columnar jointing. Well-preserved tuyas show all of these stages, for example Hjorleifshofdi in Iceland.

Products of volcano-ice interactions stand as various structures, whose shape is dependent on complex eruptive and environmental interactions. Glacial volcanism is a good indicator of past ice distribution, making it an important climatic marker. Since they are imbedded in ice, as ice retracts worldwide there are concerns that tuyas and other structures may destabalize, resulting in mass landslides. Evidence of volcanic-glacial interactions are evident in Iceland and parts of British Columbia, and it’s even possible that they play a role in deglaciation.

Phreatic eruptions

Diagram of a phreatic eruption. (key: 1. Water vapor cloud 2. Magma conduit 3. Layers of lava and ash 4. Stratum 5. Water table 6. Explosion 7. Magma chamber) © Sémhur

Phreatic eruptions (or steam-blast eruptions) are a type of eruption driven by the expansion of steam. When cold ground or surface water come into contact with hot rock or magma it superheats and explodes, fracturing the surrounding rock and thrusting out a mixture of steam, water, ash, volcanic bombs, and volcanic blocks. The distinguishing feature of phreatic explosions is that they only blast out fragments of pre-existing solid rock from the volcanic conduit; no new magma is erupted. Because they are driven by the cracking of rock stata under pressure, phreatic activity does not always result in an eruption; if the rock face is strong enough to withstand the explosive force, outright eruptions may not occur, although cracks in the rock will probably develop and weaken it, furthering future eruptions.

Often a precursor of future volcanic activity, phreatic eruptions are generally weak, although there have been exceptions. Some phreatic events may be triggered by earthquake activity, another volcanic precursor, and they may also travel along dike lines. Phreatic eruptions form base surges, lahars, avalanches, and volcanic block “rain.” They may also release deadly toxic gas able to suffocate anyone in range of the eruption.

Photos

Eruption type : Hawaiian Looking up the slope of Kilauea, a shield volcano on the island of Hawaii. In the foreground, the Puu Oo vent has erupted fluid lava to the left. The Halemaumau crater is at the peak of Kilauea, visible here as a rising vapor column in the background. The peak behind the vapor column is Mauna Loa, a volcano that is separate from Kilauea.
Eruption type: Hawaiian/Strombolian Mt. Stromboli Stromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily
Eruption type: Vulcanian Nevado del Ruiz Steam on the mountain in July 2007
Eruption type: Plinian/Ultra Plinian Krakatoa or Krakatau or Krakatao is a volcanic island in the Sunda Strait between Java and Sumatra in Indonesia (http://en.wikipedia.org/wiki/Krakatoa).

Reference:
USGS : Types of Volcanic Eruptions
University of Hawai‘i : HAWAIIAN ERUPTIONS
Wikipedia: Types of volcanic eruptions
University of California : VOLCANIC ACTIVITY AND ERUPTIONS

Preparing Boston for the “big one”

Aerial view of Back Bay, Boston. Credit: Ornella Iuorio

In 1755, a major earthquake shook the Boston area, toppling chimneys and inspiring sermons and poems about the wrath of God, such as “Earthquakes the Works of God and Tokens of his Just Displeasure” and “The Duty of a People, Under Dark Providences.” The quake, whose epicenter was about 25 miles from Massachusetts’ Cape Anne and 50 miles out to sea from Boston, measured an estimated 6.0 to 6.3 on the Richter scale. Since then, Bostonians have not had to worry much about the ground beneath them. In fact, preparing for earthquakes is probably near the bottom of the city’s to do list. But what if another major earthquake were to strike? According to SUTD-MIT postdoctoral fellow Ornella Iuorio, it would not be good.

Iuorio, who hails from earthquake-prone Italy, is spending one year at MIT, followed by a second year at the Singapore University of Technology and Design (SUTD), carrying out collaborative research with MIT Professor John Ochsendorf and SUTD professor Jeffrey Huang. For a large part of her career, Iuorio has focused on designing resilient new buildings that can withstand seismic events. Now, she is turning her attention to making historic buildings and neighborhoods earthquake-safe, with the ultimate aim of developing a tool that urban planners could use to decide which retrofit options make the most sense in a particular area.

Her project, “Smart Retrofit for Resilient Historic Cities,” is part of a comprehensive case study of Boston’s historic Back Bay neighborhood. Other researchers, including professor and MIT-SUTD International Design Center director John Fernandez and visiting scholar Nino Barbalace, have already begun studying Back Bay with an eye toward environmental retrofits. Therefore, Iuorio and Ochsendorf decided to complement that work by focusing on structural aspects.

Although it may seem unusual to examine earthquake resilience in an area seldom struck by earthquakes, Back Bay is an excellent site for the study. Like many historically valuable and beautiful urban neighborhoods, it is also extremely vulnerable to damage. Back Bay homes were primarily constructed of unreinforced masonry, which crumbles fairly easily. Furthermore, the entire development sits on what was once a mud flat, which was filled over the course of the 19th century. Although filled land is solid enough to build on, it still contains water. When the earth moves, it tends to liquefy. The fill layer can also settle and sink, exposing foundation posts to air and leaving them vulnerable to dry rot. In 1755, Boston’s population was much smaller, and Back Bay did not exist, so the Cape Anne earthquake caused only minor damage. It is estimated that an earthquake of similar magnitude today would cost billions of dollars and hundreds or even thousands of lives.

If planners hope to mitigate destruction in a place like Back Bay, the challenge, as Iuorio sees it, is to balance the various, often competing, factors involved, including safety, economic cost, environmental cost of the retrofit materials, and the historical value of the buildings. There are structural retrofits that can be easily applied, such as chains or fibrous mesh to hold the walls together as a unit. However, such retrofits can be costly, and may destroy some of the historical character of a neighborhood like Back Bay. Iuorio’s model would generate multiple solutions for structural retrofitting depending on the relative weight given to each of the factors. From the various options, city planners could choose the one that makes the most sense for the area in question.

The first phase of this project is a detailed classification of the thousand or so buildings that make up the neighborhood. Iuorio has been combing through old records and conducting on-site inspections to determine the type of construction used in each building, and to analyze potential vulnerabilities. Once this work is complete, she can begin to generate her model of retrofit options. In doing so, she says, it is important to consider the whole neighborhood, not just the individual structures. Since the buildings are directly adjacent, they act as a unit. If one begins to fold, those next to it will be affected as well. Therefore, not all retrofits would be equally effective. Reinforcing a structure at the end of a block, for example, may have more of an impact than reinforcing one in the middle of a row. Her model would make optimal suggestions based on the whole picture.

Will the mayor’s office be clamoring for the results and revising the city’s budget to allocate money for seismic retrofits? That’s unlikely, given the low probability of another major earthquake in the near future and more pressing concerns like snow removal and rising sea levels. However, the data provided by Iuorio’s study of the Back Bay neighborhood and the model she creates could serve other cities seeking to make their historic structures safer. In her second year of research, when she travels to Singapore, she may also apply the principles of her process on a larger scale, analyzing not just one neighborhood, but whole cities.

Scientists have learned a lot about why earthquakes occur since the Cape Anne event in the 18th century, but they still cannot predict when or where the next big quake may happen. Planners must make difficult decisions about how far to go in preparing for the unknown, and Iuorio is trying to make that process a little bit easier.

Note : The above story is based on materials provided by Massachusetts Institute of Technology.

New research predicts a doubling of coastal erosion by mid-century in Hawai’i

Chronic beach erosion is a global problem. Modeling now indicates that, in Hawai’i, increased sea level rise associated with the climate crisis may cause a doubling of this problem by mid-century. Credit: C. Fletcher, UH SOEST.

Chronic erosion dominates the sandy beaches of Hawai’i, causing beach loss as it damages homes, infrastructure, and critical habitat. Researchers have long understood that global sea level rise will affect the rate of coastal erosion. However, new research from scientists at the University of Hawaii – M?noa (UHM) and the Hawai’i Department of Land and Natural Resources brings into clearer focus just how dramatically Hawai’i beaches might change.

For the study, published this week in Natural Hazards, the research team developed a simple model to assess future erosion hazards under higher sea levels – taking into account historical changes of Hawai’i shorelines and the projected acceleration of sea level rise reported from the Intergovernmental Panel on Climate Change (IPCC). The results indicate that coastal erosion of Hawai’i’s beaches may double by mid-century.

Like the majority of Hawaii’s sandy beaches, most shorelines at the 10 study sites on Kauai, Oahu, and Maui are currently retreating. If these beaches were to follow current trends, an average 20 to 40 feet of shoreline recession would be expected by 2050 and 2100, respectively.

“When we modeled future shoreline change with the increased rates of sea level rise (SLR) projected under the IPCC’s “business as usual” scenario, we found that increased SLR causes an average 16 – 20 feet of additional shoreline retreat by 2050, and an average of nearly 60 feet of additional retreat by 2100,” said Tiffany Anderson, lead author and post-doctoral researcher at the UHM School of Ocean and Earth Science and Technology.

“This means that the average amount of shoreline recession roughly doubles by 2050 with increased SLR, compared to historical extrapolation alone. By 2100, it is nearly 2.5 times the historical extrapolation. Further, our results indicate that approximately 92% and 96% of the shorelines will be retreating by 2050 and 2100, respectively, except at Kailua, Oahu which is projected to begin retreating by mid-century.”

The model accounts for accretion of sand onto beaches and long-term sediment processes in making projections of future shoreline position. As part of ongoing research, the resulting erosion hazard zones are overlain on aerial photos and other geographic layers in a geographic information system to provide a tool for identifying resources, infrastructure, and property exposed to future coastal erosion.

“This study demonstrates a methodology that can be used by many shoreline communities to assess their exposure to coastal erosion resulting from the climate crisis,” said Chip Fletcher, Associate Dean at the UHM School of Ocean and Earth Science and Technology and co-author on the paper.

Mapping historical shoreline change provides useful data for assessing exposure to future erosion hazards, even if the rate of sea level rise changes in the future. The predicted increase in erosion will threaten thousands of homes, many miles of roadway and other assets in Hawai’i. Globally the asset exposure to erosion is enormous.

“With these new results government agencies can begin to develop adaptation strategies, including new policies, for safely developing the shoreline,” said Anderson.

To further improve the estimates of climate impacts, the next step for the team of researchers will be to combine the new model with assessments of increased flooding by waves.

The research was sponsored by the Hawaii Department of Land and Natural Resources, and the U.S. Geological Survey Pacific Islands Climate Science Center.

Reference:
Tiffany R. Anderson, Charles H. Fletcher, Matthew M. Barbee, L. Neil Frazer & Bradley M. Romine (2015). Doubling of coastal erosion under rising sea level by mid-century in Hawai’i. Natural Hazards doi:10.1007/s11069-015-1698-6

Note : The above story is based on materials provided by University of Hawaii at Manoa.

Japurá River

Map of the Amazon Basin with the Japurá River highlighted

The Japurá River or Caquetá River is a river about 2,820 kilometres (1,750 mi) long rising as the Caquetá River in the Andes in the Southwet of Colombia. It flows southeast into Brazil, where it is called the Japurá. The Japurá enters the Amazon River through a network of channels. It is navigable by small boats in Brazil.

The river is home to a wide variety of fish and reptiles, including enormous catfish weighing up to 91 kg (201 lb) and measuring up to 1.8 metres (5.9 ft) in length, electric eels, piranhas, turtles, and caimans. It also serves as a principal means of transportation, being plied by tiny dugout canoes, larger ones, motorboats, and riverboats known locally as lanchas. The boats carry a multitude of cargoes, sometimes being chartered, sometimes even being traveling general stores. In the Colombian section, the presence of guerrillas and soldiers often severely limits river traffic.

Much of the jungle through which the eastern Caquetá originally flowed has been cleared for pasture, crops of rice, corn, manioc, and sugar cane, and in the past two decades, particularly coca crops.

West of the Rio Negro, the Solimões River (as the Amazon’s upper Brazilian course is called) receives three more imposing streams from the northwest—the Japurá, the Içá (referred to as the Putumayo before it crosses over into Brazil), and the Napo. The Caquetá River, later to become the Japurá, rises in the Colombian Andes, nearly in touch with the sources of the Magdalena River, and augments its volume from many branches as it courses through Colombia.

The 19th-century Brazilian historian and geographer José Coelho da Gama e Abreu, the Baron of Marajó, attributed 970 kilometres (600 mi) of navigable stretches to it. Jules Crevaux, who descended it, described it as full of obstacles to navigation, the current very strong and the stream frequently interrupted by rapids and cataracts. It was initially supposed to have eight mouths, but colonial administrator Francisco Xavier Ribeiro Sampaio, in the historic report of his voyage of 1774, determined that there was but one real mouth, and that the supposed others are all furos or canos, as the diverting secondary channels of the Amazonian rivers are known.

In 1864–1868, the Brazilian government made a somewhat careful examination of the Brazilian part of the river, as far up as the rapid of Cupati. Several very easy and almost complete water routes exist between the Japurá and Negro across the low, flat intervening country. The Baron of Marajó wrote that there were six of them, and one which connects the upper Japurá with the Vaupés branch of the Negro; thus the indigenous tribes of the respective valleys have easy contact with each other.

Note : The above story is based on materials provided by Wikipedia.

A stiff new layer in Earth’s mantle

A simplified image of a slab from one of Earth’s tectonic plates sinking through the upper mantle above, through the boundary between the upper and lower mantle 410 miles deep, then stalling and pooling at a depth of 930 miles, where University of Utah experiments suggest the existence of an extremely stiff or viscous layer in Earth. Such a layer may explain why tectonic plate slabs seem to pool at 930 miles under Indonesia and South America’s Pacific coast. Below the highly viscous zone, slabs can continue to sink to the core-mantle boundary. Credit: Lowell Miyagi, University of Utah

By crushing minerals between diamonds, a University of Utah study suggests the existence of an unknown layer inside Earth: part of the lower mantle where the rock gets three times stiffer. The discovery may explain a mystery: why slabs of Earth’s sinking tectonic plates sometimes stall and thicken 930 miles underground.

The findings – published today in the journal Nature Geoscience – also may explain some deep earthquakes, hint that Earth’s interior is hotter than believed, and suggest why partly molten rock or magmas feeding midocean-ridge volcanoes such as Iceland’s differ chemically from magmas supplying island volcanoes like Hawaii’s.

“The Earth has many layers, like an onion,” says Lowell Miyagi, an assistant professor of geology and geophysics at the University of Utah. “Most layers are defined by the minerals that are present. Essentially, we have discovered a new layer in the Earth. This layer isn’t defined by the minerals present, but by the strength of these minerals.”

Earth’s main layers are the thin crust 4 to 50 miles deep (thinner under oceans, thicker under continents), a mantle extending 1,800 miles deep and the iron core. But there are subdivisions. The crust and some of the upper mantle form 60- to 90-mile-thick tectonic or lithospheric plates that are like the top side of conveyor belts carrying continents and seafloors.

Oceanic plates collide head-on with continental plates offshore from Chile, Peru, Mexico, the Pacific Northwest, Alaska, Kamchatka, Japan and Indonesia. In those places, the leading edge of the oceanic plate bends into a slab that dives or “subducts” under the continent, triggering earthquakes and volcanism as the slabs descend into the mantle, which is like the bottom part of the conveyor belt. The subduction process is slow, with a slab averaging roughly 300 million years to descend, Miyagi estimates.

Miyagi and fellow mineral physicist Hauke Marquardt, of Germany’s University of Bayreuth, identified the likely presence of a superviscous layer in the lower mantle by squeezing the mineral ferropericlase between gem-quality diamond anvils in presses. They squeezed it to pressures like those in Earth’s lower mantle. Bridgmanite and ferropericlase are the dominant minerals in the lower mantle.

The researchers found that ferropericlase’s strength starts to increase at pressures equivalent to those 410 miles deep – the upper-lower mantle boundary – and the strength increases threefold by the time it peaks at pressure equal to a 930-mile depth.

And when they simulated how ferropericlase behaves mixed with bridgmanite deep underground in the upper part of the lower mantle, they calculated that the viscosity or stiffness of the mantle rock at a depth of 930 miles is some 300 times greater than at the 410-mile-deep upper-lower mantle boundary.

“The result was exciting,” Miyagi says. “This viscosity increase is likely to cause subducting slabs to get stuck – at least temporarily – at about 930 miles underground. In fact, previous seismic images show that many slabs appear to ‘pool’ around 930 miles, including under Indonesia and South America’s Pacific coast. This observation has puzzled seismologists for quite some time, but in the last year, there is new consensus from seismologists that most slabs pool.”

How stiff or viscous is the viscous layer of the lower mantle? On the pascal-second scale, the viscosity of water is 0.001, peanut butter is 200 and the stiff mantle layer is 1,000 billion billion (or 10 to the 21st power), Miyagi says.

Slab subduction triggers earthquakes and volcanoes

For the new study, Miyagi’s funding came from the U.S. National Science Foundation and Marquardt’s from the German Science Foundation.

“Plate motions at the surface cause earthquakes and volcanic eruptions,” Miyagi says. “The reason plates move on the surface is that slabs are heavy, and they pull the plates along as they subduct into Earth’s interior. So anything that affects the way a slab subducts is, up the line, going to affect earthquakes and volcanism.”

He says the stalling and buckling of sinking slabs at due to a stiff layer in the mantle may explain some deep earthquakes higher up in the mantle; most quakes are much shallower and in the crust. “Anything that would cause resistance to a slab could potentially cause it to buckle or break higher in the slab, causing a deep earthquake.”

Miyagi says the stiff upper part of the lower mantle also may explain different magmas seen at two different kinds of seafloor volcanoes

Recycled crust and mantle from old slabs eventually emerges as new seafloor during eruptions of volcanic vents along midocean ridges – the rising end of the conveyor belt. The magma in this new plate material has the chemical signature of more recent, shallower, well-mixed magma that had been subducted and erupted through the conveyor belt several times. But in island volcanoes like Hawaii, created by a deep hotspot of partly molten rock, the magma is older, from deeper sources and less well-mixed.

Miyagi says the viscous layer in the lower mantle may be what separates the sources of the two different magmas that supply the two different kinds of volcanoes.

Another implication of the stiff layer is that “if you decrease the ability of the rock in the mantle to mix, it’s also harder for heat to get out of the Earth, which could mean Earth’s interior is hotter than we think,” Miyagi says.

He says scientists believe the average temperature and pressure 410 miles deep at the upper-lower mantle boundary is 2,800 degrees Fahrenheit and 235,000 times the atmospheric pressure on Earth’s surface. He calculates that at the viscous layer’s stiffest area, 930 miles deep, the temperature averages 3,900 degrees Fahrenheit and pressure is 640,000 times the air pressure at Earth’s surface.

Studying Earth’s interior by squeezing crystals

Such conditions prevent geophysicists from visiting Earth’s mantle, so “we know a lot more about the surface of Mars than we do Earth’s interior,” Miyagi says. “We can’t get down there, so we have to do experiments to see how these minerals behave under a wide range of conditions, and use that to simulate the behavior of the Earth.”

To do that, “you take two gem quality diamonds and trap a sample between the tips,” he says. “The sample is about the diameter of a human hair. Because the diamond tips are so small, you generate very high pressure just by turning the screws on the press by hand with Allen wrenches.”

Using diamond anvils, the researchers squeezed thousands of crystals of ferropericlase at pressures up to 960,000 atmospheres. They used ferropericlase with 10 percent and 20 percent iron to duplicate the range found in the mantle.

To observe and measure the spacing of atoms in ferropericlase crystals as they were squeezed in diamond anvils, the geophysicists bombarded the crystals with X-rays from an accelerator at Lawrence Berkeley National Laboratory in California, revealing the strength of the mineral at various pressures and allowing the simulations showing how the rock becomes 300 times more viscous at the 930-mile depth than at 410 miles.

The finding was a surprise because researchers previously believed that viscosity varied only a little bit at temperatures and pressures in the planet’s interior.

The study’s simulations also determined that just below the 930-mile-deep zone of highest viscosity, slabs sink more easily again as the lower mantle becomes less stiff, which happens because atoms can move more easily within ferropericlase crystals.

Descending slabs have been seen as deep as the core-mantle boundary 1,800 miles underground. As the bottom of the conveyor-belt-like mantle slowly moves, the slabs mix with the surrounding rock before the mixture erupts anew millions of years later and thousands of miles away at midocean ridges.

Reference:
Hauke Marquardt, Lowell Miyagi. Slab stagnation in the shallow lower mantle linked to an increase in mantle viscosity. Nature Geoscience, 2015; DOI: 10.1038/ngeo2393

Note: The above story is based on materials provided by University of Utah.

Archivists unearth rare first edition of the 1815 ‘Map that Changed the World’

William Smith 1815 map c. The Geological Society

A rare early copy of William Smith’s 1815 Geological Map of England and Wales, previously thought lost, has been uncovered by Geological Society archivists. The new map has been digitised and made available online in time for the start of celebrations of the map’s 200th anniversary, beginning with an unveiling of a plaque at Smith’s former residence by Sir David Attenborough.

The map, the first geological map of a nation ever produced, shows the geological strata of England, Wales and part of Scotland. The newly discovered copy is thought to have been one of the first ten produced by William Smith (1769-1839), who went on to produce an estimated 370 hand-coloured copies of the map in his lifetime.

Now fully restored and digitised, images of the new map can be viewed on the Geological Society’s image library from March 23 — William Smith’s birthday. It will also be on display at the Geological Society during a number of events celebrating the map’s bicentennial.

Often called ‘the Father of English Geology’, William Smith pioneered the science of stratigraphy and geological mapping. His map of England and Wales became the basis for all future geological maps of Britain, and influenced geological surveys around the world.

‘Smith’s importance to the history of our science cannot be overstated’ says John Henry, Chair of the Geological Society’s History of Geology Group. ‘His map is a remarkable piece of work. It helped shape the economic and scientific development of Britain, at a time before geological surveys existed.’

Smith’s story was popularised by Simon Winchester’s 2001 book, ‘The Map that Changed the World’, which tells the story of his relationship with the Geological Society, who produced their own geological map of Britain in 1820.

‘These maps are extremely rare’ says Henry. ‘Each one is a treasure, and to have one of the very first produced is tremendously exciting.’

Although it is difficult to estimate the value of individual William Smith maps, an early copy was recently made available for sale at £150,000. The newly discovered map was found by the Society’s then Archive Assistant Victoria Woodcock in 2014, during an audit of the Society’s archives led by Geological Society Archivist Caroline Lam.

‘The map was found among completely unrelated material, so at first I didn’t realise the significance of what I’d uncovered’ says Woodcock. ‘Once we had worked out that it was an early copy of one of the earliest geological maps ever made, I was astonished. It’s the kind of thing that anyone working in archives dreams of, and definitely the highlight of my career so far!’

The map was identified as a first edition due to its lack of serial number, and geological features which Smith was known to have updated on later versions.

‘The very first batch of maps Smith produced did not have a series number or signature’ says Henry. ‘Other indications that it is a first edition is the geology depicted on the Isle of Wight, the lack of an engraved line on the Welsh border, and lack of granite around Eskdale in the Lake District.’

Records of the Geological Society’s Council minutes from 1815 suggest the map was purchased by the Society in that year for the sum of £5 5s. Since then, its ‘disappearance’ means it has rarely been exposed to light, preserving the incredibly bright original colours.

A number of organisations, including the Geological Society, the Natural History Museum, the British Geological Survey and National Museum Wales, are joining together throughout 2015 to celebrate the bicentennial of William Smith’s map through a range of events.

‘We’re incredibly excited by the discovery’ says Geological Society President Professor David Manning. ‘It’s wonderful that the map has been restored and made publicly available in time for the bicentennial celebrations, and we’re very grateful to the sponsors who have made this possible.’

Note: The above story is based on materials provided by Geological Society of London.

Slight surface movements on the radar

Ten Sentinel-1A radar scans acquired between 7 October 2014 and 12 March 2015 were combined to create this image of ground deformation around the city of Naples, which includes the active volcanic areas of Italy’s Phlegraean Fields – or Campi Flegrei – and the Vesuvius volcano. Dark blue indicates areas that experienced an uplift of about 0.5 cm per month, while red areas show subsidence down to 0.5 per month. The purple square over the city of Naples indicates the location of the calibration point. Credit: Copernicus data (2015)/ESA/DLR Microwaves and Radar Institute/INGV/e-GEOS/GFZ–SEOM INSARAP study

Scientists are making advances in the use of satellite radar data – such as those from the Sentinel-1 mission – to monitor Earth’s changing surface.

Italy’s Phlegraean Fields – or Campi Flegrei – is a large, active volcanic area near the city of Naples and Mount Vesuvius, characterised by continuous ground deformations owing to its volcanic nature.

“In 2012, deformation rates up to 3 cm a month prompted the Italian Civil Protection Department to move from the base (green) alert level of the Campi Flegrei Emergency Plan to the attention (yellow) level,” said Sven Borgstrom from Italy’s National Institute for Geophysics and Volcanology.

“The uplift continues today: radar imagery from the Sentinel-1A satellite captured over the area between October 2014 and March 2015 show that the ground is rising by about 0.5 cm per month.”

This is just one of the many findings being presented this week at the Fringe Workshop on advances in the science and applications of ‘SAR interferometry’ held at ESRIN, ESA’s centre for Earth observation, in Frascati, Italy.

Interferometric Synthetic Aperture Radar, or InSAR, is a remote sensing technique where two or more images of the same area are combined to detect slight changes occurring between acquisitions.

Tiny changes on the ground cause changes in the radar signal and lead to rainbow-coloured interference patterns in the combined image, known as an ‘interferogram’.

The Fringe Workshop takes its name from these coloured fringes seen in the interferograms.

Small movements – down to a scale of a few millimetres – can be detected across wide areas. Tectonic plates grinding past one another, the slow ‘breathing’ of active volcanoes, the slight sagging of a city street through groundwater extraction, and even the thermal expansion of a building on a sunny day.

This year, the workshop is paying particular attention to new results from the Sentinel-1 mission. Launched in April of last year, Sentinel-1A became the first satellite in orbit for Europe’s Copernicus programme, and has been delivering important data for an array of operational and scientific applications.

In Norway’s Svalbard archipelago, Sentinel-1 data are being used to monitor ice loss from the Austfonna ice cap. Earlier this year, the satellite captured the ice cap’s outlet glacier flowing at 3 cm per day.

With over 420 participants, this year’s Fringe workshop has seen the largest turnout since its inauguration in 1991 – when four specialists met to discuss the early InSAR results from the ERS-1 mission. Radar interferometry has come a long way since, with contributions from satellites such as Envisat and now Sentinel-1A.

Note : The above story is based on materials provided by European Space Agency.

3D satellite, GPS earthquake maps isolate impacts in real time

Satellite radar image of the magnitude 6.0 South Napa earthquake. The “fringe” rainbow pattern appears where the earthquake deformed the ground’s surface, with one full cycle of the color spectrum (magenta to magenta) showing 3 centimeters of change. Satellite data like this can now be used to give researchers an understanding of an earthquake and its impacts within days. Photo courtesy of the European Space Agency.

When an earthquake hits, the faster first responders can get to an impacted area, the more likely infrastructure—and lives—can be saved.

New research from the University of Iowa, along with the United States Geological Survey (USGS), shows that GPS and satellite data can be used in a real-time, coordinated effort to fully characterize a fault line within 24 hours of an earthquake, ensuring that aid is delivered faster and more accurately than ever before.

Earth and Environmental Sciences assistant professor William Barnhart used GPS and satellite measurements from the magnitude 6.0 South Napa, California earthquake on August 24, 2014, to create a three-dimensional map of how the ground surface moved in response to the earthquake. The map was made without using traditional rapid response instruments, such as seismometers, which may not afford the same level of detail for similar events around the globe.

“By having the 3D knowledge of the earthquake itself, we can make predictions of the ground shaking, without instruments to record that ground shaking, and then can make estimates of what the human and infrastructure impacts will be— in terms of both fatalities and dollars,” Barnhart says.

The study, “Geodetic Constraints on the 2014 M 6.0 South Napa Earthquake” published in the March/April edition of Seismological Research Letters, is the first USGS example showing that GPS and satellite readings can be used as a tool to shorten earthquake response times.

And while information about an earthquake’s impact might be immediately known in an area such as southern California, Barnhart says the technique will be most useful in the developing world. The catastrophic magnitude 7.0 earthquake that hit Haiti in 2010 is the perfect example for the usefulness of this kind of tool, Barnhart says. The earthquake struck right under the capital city of Port Au Prince, killing up to 316,000 people, depending on estimates, and costing billions of dollars in aid.

“On an international scale, it dramatically reduces the time between when an earthquake happens, when buildings start to fall down, and when aid starts to show up,” Barnhart says.

To accurately map the South Napa earthquake for this study, Barnhart and a team of researchers created a complex comparison scenario.

They first used GPS and satellite readings to measure the very small- millimeter-to-centimeter-sized-displacements of the ground’s surface that were caused by the earthquake. They fed those measurements into a mathematical equation that inverts the data and relates how much the ground moved to the degree of slip on the fault plane. Slip describes the amount, timing, and distribution of fault plane movement during an earthquake.

This allowed the group to determine the location, orientation, and dimensions of the entire fault without setting foot on the ground near the earthquake. The mathematical inversion gave the researchers predictions of how much the ground might be displaced, and they compared those results to their initial estimations, bit by bit, until their predictions and observations match. The resulting model is a 3D map of fault slip beneath the Earth’s surface. The entire procedure takes only a few minutes to complete.

Nationally, there is a push to create an earthquake early-warning system, which is already being tested internally by the USGS in coordination with the University of California, Berkeley; the California Institute of Technology; and the University of Washington. While only researchers, first responders, and other officials received the early warning message, it did work in testing for the Bay Area during the Napa earthquake. Individuals in Berkeley received nearly 10 seconds of advanced warning before the ground began shaking. The information contained in Barnhart’s study could be used to create further tools for predicting the economic and human tolls of earthquakes.

“That’s why this is so important. It really was the chance to test all these tools that have been put into place,” Barnhart says. “It happened in a perfect place, because now we’re much more equipped for a bigger earthquake.”

Note : The above story is based on materials provided by University of Iowa.

Super-salamander: Earth’s top predators more than 200 million years ago

Metoposaurus algarvensis. Credit: Marc Boulay, Cossima Productions

A previously undiscovered species of crocodile-like amphibian that lived during the rise of dinosaurs was among Earth’s top predators more than 200 million years ago, a study shows.

Palaeontologists identified the prehistoric species – which looked like giant salamanders – after excavating bones buried on the site of an ancient lake in southern Portugal.

The species was part of a wider group of primitive amphibians that were widespread at low latitudes 220-230 million years ago, the team says.

The creatures grew up to 2m in length and lived in lakes and rivers during the Late Triassic Period, living much like crocodiles do today and feeding mainly on fish, researchers say.

The species – Metoposaurus algarvensis – lived at the same time as the first dinosaurs began their dominance, which lasted for over 150 million years, the team says. These primitive amphibians formed part of the ancestral stock from which modern amphibians – such as frogs and newts – evolved, researchers say.

The species were distant relatives of the salamanders of today, the team says. The discovery reveals that this group of amphibians was more geographically diverse than previously thought.

The species is the first member of the group to be discovered in the Iberian Peninsula, the team says.

Fossil remains of species belonging to the group have been found in parts of modern day Africa, Europe, India and North America. Differences in the skull and jaw structure of the fossils found in Portugal revealed they belong to a separate species.

The new species was discovered in a large bed of bones where up to several hundred of the creatures may have died when the lake they inhabited dried up, researchers say. Only a fraction of the site – around 4 square meters – has been excavated so far, and the team is continuing work there in the hope of unearthing new fossils.

Most members the group of giant salamander-like amphibians was wiped out during a mass extinction 201 million years ago, long before the death of the dinosaurs. This marked the end of the Triassic Period, when the supercontinent of Pangea – which included all the world’s present-day continents – began to break apart. The extinction wiped out many groups of vertebrates, such as big amphibians, paving the way for dinosaurs to become dominant.

The study, published in the Journal of Vertebrate Paleontology, was funded by the German Research Foundation and the National Science Foundation, the Jurassic Foundation, CNRS, Columbia University Climate Center and the Chevron Student Initiative Fund. Additional support was provided by the Municipality of Loulé, Camara Municipal de Silves and Junta de Freguesia de Salir in Portugal.

Dr Steve Brusatte, of the University of Edinburgh’s School of GeoSciences, who led the study, said: “This new amphibian looks like something out of a bad monster movie. It was as long as a small car and had hundreds of sharp teeth in its big flat head, which kind of looks like a toilet seat when the jaws snap shut. It was the type of fierce predator that the very first dinosaurs had to put up with if they strayed too close to the water, long before the glory days of T. rex and Brachiosaurus.”

Dr Richard Butler, of the School of Geography, Earth and Environmental Sciences at the University of Birmingham, said: “Most modern amphibians are pretty tiny and harmless. But back in the Triassic these giant predators would have made lakes and rivers pretty scary places to be.”

Dr Steve Brusatte will discuss his work on recently discovered species and other aspects of palaeontology at a series of events at the Edinburgh International Science Festival, which runs from 4-19 April.

Note : The above story is based on materials provided by University of Edinburgh.

World’s largest asteroid impacts found in central Australia

This is Dr Andrew Glikson with a sample of suevite — a rock with partially melted material formed during an impact. Credit: D. Seymour

A 400 kilometre-wide impact zone from a huge meteorite that broke in two moments before it slammed into the Earth has been found in Central Australia.

The crater from the impact millions of years ago has long disappeared. But a team of geophysicists has found the twin scars of the impacts – the largest impact zone ever found on Earth – hidden deep in the earth’s crust.

Lead researcher Dr Andrew Glikson from The Australian National University (ANU) said the impact zone was discovered during drilling as part of geothermal research, in an area near the borders of South Australia, Queensland and the Northern Territory.

“The two asteroids must each have been over 10 kilometres across – it would have been curtains for many life species on the planet at the time,” said Dr Glikson, from the ANU School of Archaeology and Anthropology.

The revelation of such ancient violent impacts may lead to new theories about the Earth’s history.

“Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought,” Dr Glikson said.

The exact date of the impacts remains unclear. The surrounding rocks are 300 to 600 million years old, but evidence of the type left by other meteorite strikes is lacking.

For example, a large meteorite strike 66 million years ago sent up a plume of ash which is found as a layer of sediment in rocks around the world. The plume is thought to have led to the extinction of a large proportion of the life on the planet, including many dinosaur species.

However, a similar layer has not been found in sediments around 300 million years old, Dr Glikson said.

“It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” he said.

A geothermal research project chanced on clues to the impacts while drilling more than two kilometres into the earth’s crust.

The drill core contained traces of rocks that had been turned to glass by the extreme temperature and pressure caused by a major impact.

Magnetic modelling of the deep crust in the area traced out bulges hidden deep in the Earth, rich in iron and magnesium, corresponding to the composition of the Earth mantle.

“There are two huge deep domes in the crust, formed by the Earth’s crust rebounding after the huge impacts, and bringing up rock from the mantle below,” Dr Glikson said.

The two impact zones total more than 400 kilometres across, in the Warburton Basin in Central Australia. They extend through the Earth’s crust, which is about 30 kilometres thick in this area.

The research has been published in journal Tectonophysics.

Reference:
Geophysical anomalies and quartz deformation of the Warburton West structure, central Australia , doi:10.1016/j.tecto.2014.12.010

Note : The above story is based on materials provided by The Australian National University, Canberra.

International study raises questions about cause of global ice ages

Moraines, or rocks and soil deposited by glaciers during the Last Glacial Maximum, are spread across the landscape near Mt. Cook, New Zealand’s tallest mountain, and Lake Pukaki. Credit: Aaron Putnam

A new international study casts doubt on the leading theory of what causes ice ages around the world — changes in the way the Earth orbits the sun.

The researchers found that glacier movement in the Southern Hemisphere is influenced primarily by sea surface temperature and atmospheric carbon dioxide rather than changes in the Earth’s orbit, which are thought to drive the advance and retreat of ice sheets in the Northern Hemisphere.

The findings appear in the journal Geology.

The study raises questions about the Milankovitch theory of climate, which says the expansion and contraction of Northern Hemisphere continental ice sheets are influenced by cyclic fluctuations in solar radiation intensity due to wobbles in the Earth’s orbit; those orbital fluctuations should have an opposite effect on Southern Hemisphere glaciers.

“Records of past climatic changes are the only reason scientists are able to predict how the world will change in the future due to warming. The more we understand about the cause of large climatic changes and how the cooling or warming signals travel around the world, the better we can predict and adapt to future changes,” says lead author Alice Doughty, a glacial geologist at Dartmouth College who studies New Zealand mountain glaciers to understand what causes large-scale global climatic change such as ice ages. “Our results point to the importance of feedbacks — a reaction within the climate system that can amplify the initial climate change, such as cool temperatures leading to larger ice sheets, which reflect more sunlight, which cools the planet further. The more we know about the magnitude and rates of these changes and the better we can explain these connections, the more robust climate models can be in predicting future change.”

The researchers used detailed mapping and beryllium-10 surface exposure dating of ice-age moraines — or rocks deposited when glaciers move — in New Zealand’s Southern Alps, where the glaciers were much bigger in the past. The dating method measures beryllium-10, a nuclide produced in rocks when they are struck by cosmic rays. The researchers identified at least seven episodes of maximum glacier expansion during the last ice age, and they also dated the ages of four sequential moraine ridges. The results showed that New Zealand glaciers were large at the same time that large ice sheets covered Scandinavia and Canada during the last ice age about 20,000 years ago. This makes sense in that the whole world was cold at the same time, but the Milankovitch theory should have opposite effects for the Northern and Southern Hemispheres, and thus cannot explain the synchronous advance of glaciers around the globe. Previous studies have shown that Chilean glaciers in the southern Andes also have been large at the same time as Northern Hemisphere ice sheets.

The ages of the four New Zealand ridges — about 35,500; 27,170; 20,270; and 18,290 years old — instead align with times of cooler sea surface temperatures off the coast of New Zealand based on offshore marine sediment cores. The timing of the Northern Hemisphere’s ice ages and large ice sheets is still paced by how Earth orbits the Sun, but how the cooling and warming signals are transferred around the world has not been fully explained, although ocean currents (flow direction, speed and temperature) play a significant role.

Reference:
Alice M. Doughty, Joerg M. Schaefer, Aaron E. Putnam, George H. Denton, Michael R. Kaplan, David J.a. Barrell, Bjørn G. Andersen, Samuel E. Kelley, Robert C. Finkel, And Roseanne Schwartz. Mismatch of glacier extent and summer insolation in Southern Hemisphere mid-latitudes. Geology, 2015 DOI: 10.1130/G36477.1

Note: The above story is based on materials provided by Dartmouth College.

Japan opts for massive, costly sea wall to fend off tsunamis

In this March 13, 2015 photo, a woman and a boy walk up a hill, 11-meter (36 feet) above sea level, with a tsunami evacuation sign standing at the “Millennium Hope Hills” park in Iwanuma, Miyagi prefecture, northeastern Japan. Four years after a towering tsunami ravaged much of Japan’s northeastern coast, efforts to fend off future disasters are focusing on a nearly 400-kilometer (250 mile) chain of cement sea walls, at places nearly five stories high. (AP Photo/Koji Ueda)

Four years after a towering tsunami ravaged much of Japan’s northeastern coast, efforts to fend off future disasters are focusing on a nearly 400-kilometer (250-mile) chain of cement sea walls, at places nearly five stories high.

Opponents of the 820 billion yen ($6.8 billion) plan argue that the massive concrete barriers will damage marine ecology and scenery, hinder vital fisheries and actually do little to protect residents who are mostly supposed to relocate to higher ground. Those in favor say the sea walls are a necessary evil, and one that will provide some jobs, at least for a time.

In the northern fishing port of Osabe, Kazutoshi Musashi chafes at the 12.5-meter (41-foot)-high concrete barrier blocking his view of the sea.

“The reality is that it looks like the wall of a jail,” said Musashi, 46, who lived on the seaside before the tsunami struck Osabe and has moved inland since.

Pouring concrete for public works is a staple strategy for the ruling Liberal Democratic Party and its backers in big business and construction, and local officials tend to go along with such plans.

The paradox of such projects, experts say, is that while they may reduce some damage, they can foster complacency. That can be a grave risk along coastlines vulnerable to tsunamis, storm surges and other natural disasters. At least some of the 18,500 people who died or went missing in the 2011 disasters failed to heed warnings to escape in time.

Tsuneaki Iguchi was mayor of Iwanuma, a town just south of the region’s biggest city, Sendai, when the tsunami triggered by a magnitude-9 earthquake just off the coast inundated half of its area.

A 7.2-meter (24-foot) -high sea wall built years earlier to help stave off erosion of Iwanuma’s beaches slowed the wall of water, as did stands of tall, thin pine trees planted along the coast. But the tsunami still swept up to 5 kilometers (3 miles) inland. Passengers and staff watched from the upper floors and roof of the airport as the waves carried off cars, buildings and aircraft, smashing most homes in densely populated suburbs not far from the beach.

The city repaired the broken sea walls but doesn’t plan to make them any taller. Instead, Iguchi was one of the first local officials to back a plan championed by former Prime Minister Morihiro Hosokawa to plant mixed forests along the coasts on tall mounds of soil or rubble, to help create a living “green wall” that would persist long after the concrete of the bigger, man-made structures has crumbled.

“We don’t need the sea wall to be higher. What we do need is for everyone to evacuate,” Iguchi said.

“The safest thing is for people to live on higher ground and for people’s homes and their workplaces to be in separate locations. If we do that, we don’t need to have a ‘Great Wall,'” he said.

While the lack of basic infrastructure can be catastrophic in developing countries, too heavy a reliance on such safeguards can lead communities to be too complacent at times, says Margareta Wahlstrom, head of the U.N.’s Office for Disaster Risk Reduction.

“There’s a bit of an overbelief in technology as a solution, even though everything we have learned demonstrates that people’s own insights and instincts are really what makes a difference, and technology in fact makes us a bit more vulnerable,” Wahlstrom said in an interview ahead of a recent conference in Sendai convened to draft a new framework for reducing disaster risks.

In the steelmaking town of Kamaishi, more than 1,000 people died in the 2011 tsunami, but most school students fled to safety zones immediately after the earthquake, thanks to training by a civil engineering professor, Toshitaka Katada.

The risk is not confined to Japan, said Maarten van Aalst, director of the Red Cross/Red Crescent Climate Center, who sees this in the attitudes of fellow Dutch people who trust in their low-lying country’s defenses against the sea.

“The public impression of safety is so high, they would have no idea what to do in case of a catastrophe,” he said.

Despite pockets of opposition, getting people to agree to forego the sea walls and opt instead for Hosokawa’s “Great Forest Wall” plan is a tough sell, says Tomoaki Takahashi, whose job is to win support for the forest project in local communities.

“Actually, many people are in favor of the sea walls, because they will create jobs,” said Takahashi. “But even people who really don’t like the idea also feel as if they would be shunned if they don’t go along with those who support the plan,” he said.

While the “Great Forest Wall” being planted in some areas would not stave off flooding, it would slow tsunamis and weaken the force of their waves. As waters recede, the vegetation would help prevent buildings and other debris from flowing back out to sea. Such projects would also allow rain water to flow back into the sea, a vital element of marine ecology.

Some voices in unexpected places are urging a rethink of the plan.

Prime Minister Shinzo Abe’s wife, Akie, offered numerous objections to cementing the northeast coast in a speech in New York last September. She said the walls may prevent residents from keeping an eye out for future tsunamis and would be costly to maintain for already dwindling coastal communities.

“Please do not proceed even if it’s already decided,” she said. Instead of a one-size-fits-all policy, she suggested making the plan more flexible. “I ask, is building high sea walls to shield the coast line really, really the best?”

Rikuzentakata, a small city near Osabe whose downtown area was wiped out by the tsunami, is building a higher sea wall, but also moving many tons of earth to raise the land well above sea level.

Local leader Takeshi Konno said no construction project will eliminate the need for coastal residents to protect themselves.

“What I want to stress is that no matter what people try to create, it won’t beat nature, so we humans need to find a way to co-exist with nature,” Konno said. “Escaping when there is danger . the most important thing is to save your life.”

Note : The above story is based on materials provided by The Associated Press. All rights reserved..

Did a volcanic cataclysm 40,000 years ago trigger the final demise of the Neanderthals?

Figure 4 in B.A. Black et al.: This image shows annually averaged temperature anomalies in excess of 3°C for the first year after the Campanian Ignimbrite (CI) eruption compared with spatial distribution of hominin sites with radiocarbon ages close to that of the eruption. Credit: B.A. Black et al. and the journal Geology

The Campanian Ignimbrite (CI) eruption in Italy 40,000 years ago was one of the largest volcanic cataclysms in Europe and injected a significant amount of sulfur-dioxide (SO2) into the stratosphere. Scientists have long debated whether this eruption contributed to the final extinction of the Neanderthals. This new study by Benjamin A. Black and colleagues tests this hypothesis with a sophisticated climate model.

Black and colleagues write that the CI eruption approximately coincided with the final decline of Neanderthals as well as with dramatic territorial and cultural advances among anatomically modern humans. Because of this, the roles of climate, hominin competition, and volcanic sulfur cooling and acid deposition have been vigorously debated as causes of Neanderthal extinction.

They point out, however, that the decline of Neanderthals in Europe began well before the CI eruption: “Radiocarbon dating has shown that at the time of the CI eruption, anatomically modern humans had already arrived in Europe, and the range of Neanderthals had steadily diminished. Work at five sites in the Mediterranean indicates that anatomically modern humans were established in these locations by then as well.”

“While the precise implications of the CI eruption for cultures and livelihoods are best understood in the context of archaeological data sets,” write Black and colleagues, the results of their study quantitatively describe the magnitude and distribution of the volcanic cooling and acid deposition that ancient hominin communities experienced coincident with the final decline of the Neanderthals.

In their climate simulations, Black and colleagues found that the largest temperature decreases after the eruption occurred in Eastern Europe and Asia and sidestepped the areas where the final Neanderthal populations were living (Western Europe). Therefore, the authors conclude that the eruption was probably insufficient to trigger Neanderthal extinction.

However, the abrupt cold spell that followed the eruption would still have significantly impacted day-to-day life for Neanderthals and early humans in Europe. Black and colleagues point out that temperatures in Western Europe would have decreased by an average of 2 to 4 degrees Celsius during the year following the eruption. These unusual conditions, they write, may have directly influenced survival and day-to-day life for Neanderthals and anatomically modern humans alike, and emphasize the resilience of anatomically modern humans in the face of abrupt and adverse changes in the environment.

Reference:
B. A. Black, R. R. Neely, M. Manga. Campanian Ignimbrite volcanism, climate, and the final decline of the Neanderthals. Geology, 2015; DOI: 10.1130/G36514.1

Note: The above story is based on materials provided by Geological Society of America.

Crocodile ancestor was top predator before dinosaurs roamed North America

This is a life reconstruction of Carnufex carolinensis. Credit: Copyright Jorge Gonzales. Open access

A newly discovered crocodilian ancestor may have filled one of North America’s top predator roles before dinosaurs arrived on the continent. Carnufex carolinensis, or the “Carolina Butcher,” was a 9-foot long, land-dwelling crocodylomorph that walked on its hind legs and likely preyed upon smaller inhabitants of North Carolina ecosystems such as armored reptiles and early mammal relatives.

Paleontologists from North Carolina State University and the North Carolina Museum of Natural Sciences recovered parts of Carnufex’s skull, spine and upper forelimb from the Pekin Formation in Chatham County, North Carolina. Because the skull of Carnufex was preserved in pieces, it was difficult to visualize what the complete skull would have looked like in life. To get a fuller picture of Carnufex’s skull the researchers scanned the individual bones with the latest imaging technology — a high-resolution surface scanner. Then they created a three-dimensional model of the reconstructed skull, using the more complete skulls of close relatives to fill in the missing pieces.

The Pekin Formation contains sediments deposited 231 million years ago in the beginning of the Late Triassic (the Carnian), when what is now North Carolina was a wet, warm equatorial region beginning to break apart from the supercontinent Pangea. “Fossils from this time period are extremely important to scientists because they record the earliest appearance of crocodylomorphs and theropod dinosaurs, two groups that first evolved in the Triassic period, yet managed to survive to the present day in the form of crocodiles and birds,” says Lindsay Zanno, assistant research professor at NC State, director of the Paleontology and Geology lab at the museum, and lead author of a paper describing the find. “The discovery of Carnufex, one of the world’s earliest and largest crocodylomorphs, adds new information to the push and pull of top terrestrial predators across Pangea.”

Typical predators roaming Pangea included large-bodied rauisuchids and poposauroids, fearsome cousins of ancient crocodiles that went extinct in the Triassic Period. In the Southern Hemisphere, “these animals hunted alongside the earliest theropod dinosaurs, creating a predator pile-up,” says Zanno. However, the discovery of Carnufex indicates that in the north, large-bodied crocodylomorphs, not dinosaurs, were adding to the diversity of top predator niches. “We knew that there were too many top performers on the proverbial stage in the Late Triassic,” Zanno adds. “Yet, until we deciphered the story behind Carnufex, it wasn’t clear that early crocodile ancestors were among those vying for top predator roles prior to the reign of dinosaurs in North America.”

As the Triassic drew to a close, extinction decimated this panoply of predators and only small-bodied crocodylomorphs and theropods survived. “Theropods were ready understudies for vacant top predator niches when large-bodied crocs and their relatives bowed out,” says Zanno. “Predatory dinosaurs went on to fill these roles exclusively for the next 135 million years.”

Still, ancient crocodiles found success in other places. “As theropod dinosaurs started to make it big, the ancestors of modern crocs initially took on a role similar to foxes or jackals, with small, sleek bodies and long limbs,” says Susan Drymala, graduate student at NC State and co-author of the paper. “If you want to picture these animals, just think of a modern day fox, but with alligator skin instead of fur.”

Reference:
Lindsay E. Zanno, Susan Drymala, Sterling J. Nesbitt, Vincent P. Schneider. Early crocodylomorph increases top tier predator diversity during rise of dinosaurs. Scientific Reports, 2015; 5: 9276 DOI: 10.1038/srep09276

Note: The above story is based on materials provided by North Carolina State University.

Protein the clue to solving a Darwinian mystery

Scientists at the University of York provided the key to solving the evolutionary puzzle surrounding what Charles Darwin called the ‘strangest animals ever discovered’. Credit: Copyright Peter Schouten

Scientists have resolved pieces of a nearly 200-year-old evolutionary puzzle surrounding the group of mammals that Charles Darwin called the “strangest animals ever discovered.” New research led by the Natural History Museum, the American Museum of Natural History and the University of York shows that South America’s native ungulates, or hooved mammals — the last of which disappeared only 10,000 years ago — are actually related to mammals like horses rather than elephants and other species with ancient evolutionary ties to Africa as some taxonomists have maintained. Published today in the journal Nature, the findings are based on fossil protein sequences, which allow researchers to peek back in time up to 10 times farther than they can with DNA.

Ian Barnes, Research Leader at the Natural History Museum and one of the paper’s authors, explained: “Although the bones of these animals had been studied for over 180 years, no clear picture of their origins had been reached. Our analyses began by investigating ancient DNA to try to resolve the problem.”

“Fitting South American ungulates to the mammalian family tree has always been a major challenge for palaeontologists, because anatomically they were these weird mosaics, exhibiting features found in a huge variety of quite unrelated species living all over the place,” said Ross MacPhee, one of the paper’s authors and a curator in the American Museum of Natural History’s Department of Mammalogy. “This is what puzzled Darwin and his collaborator Richard Owen so much in the early 19th century. With all of these conflicting signals, they couldn’t say whether these ungulates were related to giant rodents, or elephants, or camels — or what have you.”

However, the team soon realized that ancient DNA — that is, genetic material extracted from fossils — did not survive in these fossils, because the DNA molecule survives poorly in the warm, wet conditions like those typical of South America. The breakthrough came when the researchers switched to analysing collagen, a structural protein found in all animal bones that can survive for a million years or more in a wide range of conditions. The chemical structure of the amino acids that make up a protein is ultimately dictated by specific coding sequences in the organism’s DNA. Because of this key relationship, amino acid compositions of the same protein in different species can be analysed and compared, providing insight into how closely the species are related.

“People have been successful in retrieving collagen sequences from specimens dating up to 4 million years old, and this is just the start,” said University of York Professor Matthew Collins, whose lab did the sequencing work. “On theoretical grounds, with material recovered from permafrost conditions, we might be able to reach back 10 million years.”

The scientists used proteomic analysis to screen 48 fossils of Toxodon platensis and Macrauchenia patachonica, the very species whose remains Darwin discovered 180 years ago in Uruguay and Argentina. “By selecting only the very best preserved bone specimens and with various improvements in proteomic analysis, we were able to obtain roughly 90 percent of the collagen sequence for both species,” said lead author Frido Welker, a Ph.D. student at the Max Planck Institute for Evolutionary Anthropology and the University of York. “This opens the way for various other applications in paleontology and paleoanthropology, which we are currently exploring.”

With modern techniques, the researchers were able to conclusively show that the closest living relatives of these species were the perissodactyls, the group that includes horses, rhinos, and tapirs. This makes them part of Laurasiatheria, one of the major groups of placental mammals. The molecular evidence corroborates a view held by some leading paleontologists that the ancestors of these South American ungulates came from North America more than 60 million years ago, probably just after the mass extinction that killed off non-avian dinosaurs and many other vertebrates.

Reference:
Frido Welker, Matthew J. Collins, Jessica A. Thomas, Marc Wadsley, Selina Brace, Enrico Cappellini, Samuel T. Turvey, Marcelo Reguero, Javier N. Gelfo, Alejandro Kramarz, Joachim Burger, Jane Thomas-Oates, David A. Ashford, Peter D. Ashton, Keri Rowsell, Duncan M. Porter, Benedikt Kessler, Roman Fischer, Carsten Baessmann, Stephanie Kaspar, Jesper V. Olsen, Patrick Kiley, James A. Elliott, Christian D. Kelstrup, Victoria Mullin et al. Ancient proteins resolve the evolutionary history of Darwin’s South American ungulates. Nature, 2015 DOI: 10.1038/nature14249

Note: The above story is based on materials provided by University of York.

Iron rain fell on early Earth, new Z machine data supports

An artist’s concept shows a celestial body about the size of our moon slamming at great speed into a body the size of Mercury. Credit: Image courtesy of NASA/JPL-Caltech

Researchers at Sandia National Laboratories’ Z machine have helped untangle a long-standing mystery of astrophysics: why iron is found spattered throughout Earth’s mantle, the roughly 2,000-mile thick region between Earth’s core and its crust.

At first blush, it seemed more reasonable that iron arriving from collisions between Earth and planetesimals — ranging from several meters to hundreds of kilometers in diameter — during Earth’s late formative stages should have powered bullet-like directly to Earth’s core, where so much iron already exists.

A second, correlative mystery is why the moon proportionately has much less iron in its mantle than does Earth. Since the moon would have undergone the same extraterrestrial bombardment as its larger neighbor, what could explain the relative absence of that element in the moon’s own mantle?

To answer these questions, scientists led by Professor Stein Jacobsen at Harvard University and Professor Sarah Stewart at the University of California at Davis (UC Davis) wondered whether the accepted theoretical value of the vaporization point of iron under high pressures was correct. If vaporization occurred at lower pressures than assumed, a solid piece of iron after impact might disperse into an iron vapor that would blanket the forming Earth instead of punching through it. A resultant iron-rich rain would create the pockets of the element currently found in the mantle.

As for the moon, the same dissolution of iron into vapor could occur, but the satellite’s weaker gravity would be unable to capture the bulk of the free-floating iron atoms, explaining the dearth of iron deposits on Earth’s nearest neighbor.

Looking for experimental rather than theoretical values, researchers turned to Sandia’s Z machine and its Fundamental Science Program, coordinated by Sandia manager Thomas Mattsson. This led to a collaboration among Sandia, Harvard University, UC Davis, and Lawrence Livermore National Laboratory (LLNL) to determine an experimental value for the vaporization threshold of iron that would replace the theoretical value used for decades.

Rick Kraus at LLNL (formerly at Harvard) and Sandia researchers Ray Lemke and Seth Root used Z to accelerate metals to extreme speeds using high magnetic fields. The researchers created a target that consisted of an iron plate 5 millimeters square and 200 microns thick, against which they launched aluminum flyer plates travelling up to 25 kilometers per second. At this impact pressure, the powerful shock waves created in the iron cause it to compress, heat up and — in the zero pressure resulting from waves reflecting from the iron’s far surface — vaporize.

The result, published March 2 in Nature Geosciences under the title “Impact vaporization of planetesimal cores in the late stages of planet formation,” shows the shock pressure experimentally required to vaporize iron is approximately 507 gigapascals (GPa), undercutting by more than 40 percent the previous theoretical estimate of 887 GPa. Astrophysicists say that this lower pressure is readily achieved during the end stages of planetary growth through accretion.

Principal investigator Kraus said, “Because planetary scientists always thought it was difficult to vaporize iron, they never thought of vaporization as an important process during the formation of Earth and its core. But with our experiments, we showed that it’s very easy to impact-vaporize iron.”

He continued, “This changes the way we think of planet formation, in that instead of core formation occurring by iron sinking down to the growing Earth’s core in large blobs (technically called diapirs), that iron was vaporized, spread out in a plume over the surface of Earth and rained out as small droplets. The small iron droplets mixed easily with the mantle, which changes our interpretation of the geochemical data we use to date the timing of Earth’s core formation.”

Reference:
Richard G. Kraus, Seth Root, Raymond W. Lemke, Sarah T. Stewart, Stein B. Jacobsen, Thomas R. Mattsson. Impact vaporization of planetesimal cores in the late stages of planet formation. Nature Geoscience, 2015; DOI: 10.1038/ngeo2369

Note: The above story is based on materials provided by DOE/Sandia National Laboratories.

Beetles beat out extinction

The rich diversity seen in modern-day beetles could have more to do with extinction resistance than a high rate of new species originations. Credit: Dena Smith

Today’s rich variety of beetles may be due to an historically low extinction rate rather than a high rate of new species emerging, according to a new study. These findings were revealed by combing through the fossil record.

“Much of the work to understand why beetles are diverse has really focused on what promotes speciation,” says lead author Dena Smith, Curator of Invertebrate Paleontology and Associate Professor of Geological Sciences at the University of Colorado Museum of Natural History. “By looking at the fossil history of the group, we can see that extinction, or rather lack of extinction may be just as important, if not more important, than origination. Perhaps we should be focusing more on why beetles are so resistant to extinction.” Smith’s study with her coauthor, Jonathan Marcot, Research Assistant Professor of Animal Biology at the University of Illinois, will appear in the Proceedings of the Royal Society B.

To fully explore the evolution of the insect order, Coleoptera, Smith and Marcot used publications that document the fossil record of beetles from international literature as far back as the early 19th century and open access database projects including the EDNA Fossil Insect Database and the Catalogue of Fossil Coleoptera. The team constructed a database of 5,553 beetle species from 221 unique locations. Given the patchy nature of the data at the species level, they performed analyses at the family level and found that the majority of families that are living today also preserved in the fossil record.

The study explores beetles as far back as their origins in the Permian period, 284 million years ago. When compared to the fossil record of other animal groups such as clams, corals, and vertebrates, beetles have among the lowest family-level extinction rates ever calculated. In fact, no known families in the largest beetle subgroup, Polyphaga, go extinct in their evolutionary history. The negligible beetle extinction rate is likely caused by their flexible diets, particularly in the Polyphaga, which include algae, plants, and other animals.

“There are several things about beetles that make them extremely flexible and able to adapt to changing situations,” Smith says. She points to beetles’ ability to metamorphose–a trait shared by many insects–when considering their environmental flexibility. Soft-bodied larvae vary greatly from winged, exoskeleton-ensconced adults. “This means that they can take advantage of very different types of habitats as a larva and then as an adult,” she adds. “Adult beetles can be highly mobile and research that has focused on glacial-interglacial cycles has shown that they can move quickly in response to any climate fluctuations.”

The study explores beetles as far back as their origins in the Permian period, 284 million years ago. Both authors emphasize that illustrating such a history would not have been possible without the fossil record–an often underutilized resource in exploring the evolution of insects.

“I think people have been hesitant to jump into studying insect fossils because there has been the misperception that they are so fragile and rarely fossilize,” Smith says. “I am hoping that this study demonstrates that the fossil record is quite good and can be used in many ways to study the evolution of this diverse and important group.”

Marcot adds, “Not only have these groups gone un-studied, but there are certain things that we can learn from the fossil record that we just can’t learn any place else.”

Other insect groups might be similar to Coleoptera in terms of their extinction resistance, and Smith hopes that their work will inspire other entomologists to delve into the fossil record of their favorite insect. For now she is actively working to digitize more fossil specimens, paving the way for future studies to be conducted on a finer scale. The project, known as the Fossil Insect Collaborative and funded by the National Science Foundation, is expected to make available more than half a million fossil insect specimens from the major U.S. collections–many with associated images–in a searchable online database.

“Being a curator of a museum collection, I know that there are many species in our cabinets that have not yet been studied and described,” Smith says. “Once we are able to bring those specimens out of the cabinets and make them more accessible to the broader research community, I think we will be able to look at species level patterns and other really interested questions about the macroevolutionary history of insect groups.”

Reference:
D. M. Smith, J. D. Marcot. The fossil record and macroevolutionary history of the beetles. Proceedings of the Royal Society B: Biological Sciences, 2015; 282 (1805): 20150060 DOI: 10.1098/rspb.2015.0060

Note : The above story is based on materials provided by National Evolutionary Synthesis Center (NESCent).

Unaweep canyon and Earth’s deep-time past

This is a digital elevation model of the Uncompahgre Plateau and greater study region with key features labeled. Credit: Figure 1 from Soreghan et al.; Soreghan et al. and Geosphere

Unaweep Canyon is a puzzling landscape — the only canyon on Earth with two mouths. First formally documented by western explorers mapping the Colorado Territory in the 1800s, Unaweep Canyon has inspired numerous hypotheses for its origin. This new paper for Geosphere by Gerilyn S. Soreghan and colleagues brings together old and new geologic data of this region to further the hypothesis that Unaweep Canyon was formed in multiple stages.

The inner gorge originated ~300 million years ago, was buried, was then revealed about five million years ago when the ancestral Gunnison River began incising the Uncompaghre Plateau as part of the incision of the larger Colorado Plateau, and then the Gunnison River then abandoned the canyon upon landslide damming, ultimately joining the Colorado River.

This work highlights that incision of the Colorado Plateau by the Colorado River and its tributaries (including the Gunnison River) began synchronously across the entire Plateau, linking the incision of the Grand Canyon on the southern Plateau to events on the northern Plateau. It also highlights the intriguing possibility of preservation of very ancient landscapes from Earth’s deep-time past, and the role of exhumation of those landscapes in shaping the modern face of the planet.

Reference:
G. S. Soreghan, D. E. Sweet, S. N. Thomson, S. A. Kaplan, K. R. Marra, G. Balco, T. M. Eccles. Geology of Unaweep Canyon and its role in the drainage evolution of the northern Colorado Plateau. Geosphere, 2015; DOI: 10.1130/GES01112.1

Note: The above story is based on materials provided by Geological Society of America.

First European sea turtles became extinct due to changing sea levels

Reconstruction of ‘Indeterminate Plesiochelyidae’ on a coastal landscape of Upper Jurassic Iberia. Credit: Iván Gromicho

Little is known about the oldest sea turtles that inhabited Earth millions of years ago. The finding in the Baetic Cordillera, in Jaén, of the remains of a supposed new species of turtle, Hispaniachelys prebetica — considered the oldest in southern Europe — brought new clues six years ago. However, it was still not clear what group the primitive turtle belonged to.

To resolve the matter, Adán Pérez-García, a researcher in the Evolutionary Biology group of the UNED, studied the as-yet-unanalysed fossils of the specimen, reinterpreted some of its features and provided new information on the morphology of these reptiles. The results marked a radical shift in fossil interpretation.

As Pérez-García clarifies: “Hispaniachelys prebetica cannot be recognised as a valid species. Nevertheless, it is identified as a member of a group of turtles exclusive to the European Jurassic called Plesiochelyidae, which were very diverse.”

The study, published in ‘Acta Palaeontologica Polonica’, demonstrates that some of the characteristics of Hispaniachelys prebetica, such as the relatively large carapace, were no different from turtles of the Plesiochelyidae group. However, due to the scarce information about this, the only example, “the specimen is reinterpreted as an indeterminate member of this group of turtles,” the study expounds.

According to the researcher, “Hispaniachelys prebetica is no longer deemed a valid name but is now what is technically known as nomen dubium,” and he adds that a more precise classification ‘Indeterminate Plesiochelyidae’ is not possible. “This specimen is an indeterminate species of Plesiochelyidae, which could be one of the other previously defined species,” the scientist asserts.

Clumsy Jurassic turtles

Around 160 million years ago, in countries such as the United Kingdom, France, Switzerland, Germany, Portugal and Spain, a group of primitive turtles lived called Plesiochelyids, which “do not resemble any currently existing turtle,” the expert continues. In Spain there were several species, many of them recently identified, on which there is abundant material. Now, with the identification of the specimen in Jaén, the record expands to attribute it to this group.

These European reptiles inhabited warm, shallow seas of the continent, but “they were not as agile in this environment as today’s sea turtles, who are able to cover very large distances and cross seas and even oceans,” the expert explains. “Due to their anatomy, these Jurassic turtles were restricted to coastlines.”

Because of their dependency on coastal environments, the changes in the sea level which occurred at the end of the Jurassic period — around 145 million years ago — had a drastic impact upon the environments they lived in. As a result, “these turtles, in addition to other groups of sea reptiles, became extinct at that time,” Pérez-García confirms.

Through several projects he is carrying out at the Geology Centre at the University of Lisbon (Portugal) and the UNED, the researcher continues working on reviewing Plesiochelyidae on the Iberian Peninsula and other regions in Europe. “We are attempting to discover the real diversity in the fossil record of this, until now, little-known group,” he concludes.

Reference:
Adán Pérez-García. Reinterpretation of the Spanish Late Jurassic “Hispaniachelys prebetica” as an indeterminate plesiochelyid turtle (Testudines, Pancryptodira). Acta Palaeontologica Polonica, 2013; DOI: 10.4202/app.2012.0115

Note: The above story is based on materials provided by Plataforma SINC.

Seismic study aims to map Earth’s interior in 3-D

Using a technique that is similar to a medical CT (“CAT”) scan, researchers at Princeton are using seismic waves from earthquakes to create images of the Earth’s subterranean structures — such as tectonic plates, magma reservoirs and mineral deposits — which will help better understand how earthquakes and volcanoes occur. The team is using the Titan supercomputer at the U.S. Department of Energy’s Oak Ridge National Laboratory in Tennessee to map the entire mantle, creating a three-dimensional map of the Earth to a depth of 1,800 miles below the surface. Credit: Ebru Bozdağ, University of Nice Sophia Antipolis, and David Pugmire, Oak Ridge National Laboratory

When a 7.9-magnitude earthquake struck central China’s Sichuan province in 2008, seismic waves rippled through the region, toppling apartment houses in the city of Chengdu and swaying office buildings 1,000 miles away in Shanghai.

Though destructive, earthquakes provide benefit in one respect: they help researchers learn about the structure of the Earth, which in turn could lead to more accurate predictions of damage from future quakes and volcanic activity. By eavesdropping on the seismic vibrations of quakes as they rumble through the Earth, researchers can detect the existence of structures such as mineral deposits, subterranean lakes, and upwellings of magma. Thanks to a growing earthquake detection network and superfast computers, geoscientists are now able to explore the Earth’s interior, a region that has been more inaccessible than the deepest ocean or the farthest planet in our solar system.

Princeton geosciences professor Jeroen Tromp and his team have embarked on an ambitious project to use earthquakes to map the Earth’s entire mantle, the semisolid rock that stretches to a depth of 1,800 miles, about halfway down to the planet’s center and about 300 times deeper than humans have drilled. For the task, his team will use one of the world’s fastest supercomputers, Titan, which can perform more than 20 quadrillion calculations per second and is located at the Department of Energy’s Oak Ridge National Laboratory in Tennessee.

“Seismology is changing at a fundamental level due to advances in computing power,” said Tromp, who earned his Ph.D. in geology from Princeton and is Princeton’s Blair Professor of Geology, professor of applied and computational mathematics, and associate director of the Princeton Institute for Computational Science and Engineering. “If someone had told me what seismology would look like 20 years from when I graduated from Princeton in 1992, I would have never believed it.”

For the project, Tromp will use seismic waves from roughly 3,000 quakes of magnitude 5.5 and greater, recorded at thousands of seismographic stations worldwide and distributed via the National Science Foundation’s Incorporated Research Institutions for Seismology. These stations make recordings, or seismograms, that detail the movement produced by seismic waves, which typically travel at speeds of several miles per second and last several minutes.

“The ultimate goal is a 3-D map on a global scale,” said Tromp, who expects to have preliminary results at the end of this year. “We are specifically interested in the structure of mantle upwellings and plumes,” he said, “but much of it will be investigating the images for unusual features.”

These unusual features could include, for example, a fragment of a tectonic plate that broke off and sank into the mantle. The resulting map could tell seismologists more about the precise locations of underlying tectonic plates, which can trigger earthquakes when they shift or slide against each other. The maps could also reveal the locations of magma that, if it comes to the surface, causes volcanic activity.

As seismic waves travel, they slow or speed up depending on the density, temperature and type of rock. For example, they slow down when traveling through an underground aquifer or magma. By combining seismograms from many earthquakes recorded at many stations, geologists can produce a three-dimensional model of the structure under the Earth’s surface.

This technique is called seismic tomography and is analogous to computerized tomography used in medical (“CAT”) scans, in which a scanner captures a series of X-ray images from different viewpoints, creating cross-sectional images that can be combined into 3-D images.

Over the past eight years, Tromp has been at the forefront of research on how to improve seismic tomography to obtain high-definition, accurate images of the Earth’s interior. Past approaches for making these images incorporate only three types of seismic waves: primary or compressional waves, secondary or shear waves, and surface waves. Tromp has pioneered techniques for using much more of the information in seismograms, utilizing both waves that travel from the quake epicenter to the detector as well as those that travel from the detector to the quake, which are called adjoint waves.

“If we are going to do better, we need to use everything in the picture, in other words, everything and anything in the seismograms,” Tromp said.

Tromp’s team feeds data from seismograms into a computer model, which simulates each wave as it propagates from the epicenter. The resulting “synthetic seismograms” are compared to real seismograms, and the differences are fed back into the model to improve it. The researchers do this over and over, comparing data with simulations and extracting differences. With each pass, they improve their model.

Before attempting to map the entire Earth, Tromp and his team, with funding from the National Science Foundation, showed that their technique worked in smaller regions, first in Southern California using data from 143 quakes, which was published in the journal Science in 2009, and later in Europe using 190 quakes. The Europe study, published in the journals Nature Geosciences in 2012 and Science in 2013, included work by then graduate student Hejun Zhu, now a postdoctoral researcher at the University of Texas-Austin; postdoctoral researcher Ebru Bozdağ, now an assistant professor at the University of Nice Sophia Antipolis; postdoctoral researcher Daniel Peter, who today is a senior scientist at ETH Zurich; and David Pugmire, a visualization scientist at the Oak Ridge Leadership Computing Facility (OLCF).

More recently, Tromp and collaborators published a study on the structure of the Earth beneath East Asia using 227 quakes, including the 2008 quake in Sichuan. The study, accepted for publication in the Journal of Geophysical Research: Solid Earth and conducted with colleagues at Rice University, the University of Toronto, the China University of Petroleum and the China Earthquake Administration, plumbed East Asia to a depth of 560 miles.

These smaller projects enabled Tromp’s team to compete for and obtain 50 million processor hours on Titan this year as part of a prestigious 2015 Innovative and Novel Computational Impact of Theory and Experiment (INCITE) award from the U.S. Department of Energy.

One of the major challenges for Tromp’s team was to figure out how to compare real data to modeled results, which are given in the language of the computer code that created them. “You need to bring the data and the simulation into the same framework, to put them on equal footing,” Tromp said. “Then you can start to compare real data to the simulations and extract differences.”

Nor is Titan easy to program given its unique architecture—it is supercharged with graphics processors originally developed for gaming systems. “The challenge is to get the data onto the graphics cards and get the cards to do the right thing with the data,” Tromp said.

For postdoctoral researcher Matthieu Lefebvre, who earned a Ph.D. in mathematics prior to coming to Princeton, working on the project was an opportunity to work with one of the most powerful computers on the planet. “The project offers a lot of opportunities and challenges, such as how to optimize computational algorithms and workflows at large scales,” Lefebvre said.

For help, Tromp relies on the OLCF’s “science liaisons,” experts in mathematics and computer science such as Judith Hill who work with university scientists to prepare code for Titan.

“The team’s seismographic data originally were laid out in such a way that a significant fraction of the simulation time would be spent reading the data off the disks,” Hill said. “Professor Tromp worked with our data liaisons to develop a new data format for the seismic community that was optimal for large-scale computers such as Titan and the file systems that go along with them.”

The OLCF is also helping the Princeton team with the task of visualizing the results of the calculations. “Once you run the models, you have to mine the images to see what you have,” Tromp explained. “You need techniques like volume rendering and feature extraction to show you what you have discovered. For example, you might discover a new plume, an upwelling of magma that traverses the mantle, or you might discover hot spots.”

Added Tromp: “You don’t know what it is you are looking for, you are hunting. That is the real challenge, and that is the wonderful part of this project—waiting to see what we will discover.”

Reference:
“Mapping tectonic deformation in the crust and upper mantle beneath Europe and the North Atlantic Ocean.” Science 23 August 2013: Vol. 341 no. 6148 pp. 871-875. DOI: 10.1126/science.1241335

“Multi-parameter adjoint tomography of the crust and upper mantle beneath East Asia – Part I: Model construction and comparisons” Journal of Geophysical Research: Solid Earth. DOI: 10.1002/2014JB011638

Note : The above story is based on materials provided by Princeton University.

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