Debris Flows On Arctic Sand Dunes Are Similar to Dark Dune Spot-Seepage Flows On Mars

September 8, 2013

The Sheldon Glacier with Mount Barre in the background, is seen from Ryder Bay near Rothera Research Station, Adelaide Island, Antarctica (Photo : Reuters)

A team of scientists from Southwest Research Institute (SwRI) has demonstrated that frozen water in the form of snow or frost can melt to form debris flows on sunward-facing slopes of sand dunes in the Alaskan arctic at air temperatures significantly below the melting point of water. The debris flows consist of sand mixed with liquid water that cascade down steep slopes.

SwRI scientists made their observations at the Great Kobuk Sand Dunes, in Kobuk Valley National Park, Alaska. This site serves as an Earth-based cold-climate “analog” to dunes on Mars. Debris flows formed on days when air temperatures measured continuously by the team remained below the melting point of water. Very few minutes of above-freezing ground surface temperatures are needed to locally melt frozen water and mobilize sand down steep slopes.

The scientists hypothesize that fresh patches of wind-deposited dark sand on bright white snow caused local hot spots to form where solar radiation was absorbed by the sand and conducted into the underlying snow. This enabled meltwater to briefly form and sand to be mobilized despite subfreezing local air temperatures. A similar mechanism may be responsible for triggering debris flows on frozen Martian sand dunes. The Alaskan debris flows formed at ground temperatures that may correspond to those occurring locally and seasonally on the surface of Mars, said hydrogeologist Dr. Cynthia Dinwiddie, a principal engineer in SwRI’s Geosciences and Engineering Division.

The Alaskan debris flows are morphologically similar to small, defrosting-related “dark dune spot” seepage flows that seasonally form in late winter on frost-covered Martian sand dunes. Such features were described in detail by a number of other researchers, and in particular by a team from Collegium Budapest, Institute for Advanced Study in Hungary.

Dark dune spot seepage flow features gave rise to the popularly known “trees on Mars” optical illusion that was associated with Mars Reconnaissance Orbiter HiRISE images of the flows. Such imagery was published “upside-down” online in an inverted orientation relative to the downward direction of gravity flows on dune slip faces, thus creating the tree-like dendritic pattern.

Dark dune spots are non-uniformly distributed on all frost-covered dune surfaces on Mars, but only those occurring near dune crests or on steep slip faces result in downslope flows. A thin brine layer may form and flow downslope on Martian sand dunes after the seasonally deposited carbon dioxide frost layer has begun to locally sublimate. Because of preferential energy adsorption by these dark, ice-free surfaces, localized heating and thawing at scales too small for orbital sensors to identify may yield briny Martian debris flows under current climate conditions.

Note : The above story is based on materials provided by Southwest Research Institute.

Beneath Earth’s Surface, Scientists Find Long ‘Fingers’ of Heat

September 6, 2013

Slow-moving seismic waves, hotter than surrounding material, interact with plumes rising from the mantle to affect the formation of hotspot volcanic islands. (Credit: Illustration: Scott French)

Scientists seeking to understand the forces at work beneath the surface of Earth have used seismic waves to detect previously unknown “fingers” of heat, some of them thousands of miles long, in Earth’s upper mantle. Their discovery, published Sept. 5 in Science Express, helps explain the “hotspot volcanoes” that give birth to island chains such as Hawai’i and Tahiti.

Many volcanoes arise at collision zones between the tectonic plates, but hotspot volcanoes form in the middle of the plates. Geologists have hypothesized that upwellings of hot, buoyant rock rise as plumes from deep within Earth’s mantle — the layer between the crust and the core that makes up most of Earth’s volume — and supply the heat that feeds these mid-plate volcanoes.

But some hotspot volcano chains are not easily explained by this simple model, a fact which suggests there are more complex interactions between these hot plumes and the upper mantle. Now, a computer modeling approach, developed by University of Maryland seismologist Vedran Lekic and colleagues at the University of California Berkeley, has produced new seismic wave imagery which reveals that the rising plumes are, in fact, influenced by a pattern of finger-like structures carrying heat deep beneath Earth’s oceanic plates.

Seismic waves are waves of energy produced by earthquakes, explosions and volcanic eruptions, which can travel long distances below Earth’s surface. As they travel through layers of different density and elasticity, their shape changes. A global network of seismographs records these changing waveforms. By comparing the waveforms from hundreds of earthquakes recorded at locations around the world, scientists can make inferences about the structures through which the seismic waves have traveled.

The process, known as seismic tomography, works in much the same way that CT scans (computed tomography) reveal structures hidden beneath the surface of the human body. But since we know much less about the structures below Earth’s surface, seismic tomography isn’t easy to interpret. “The Earth’s crust varies a lot, and being able to represent that variation is difficult, much less the structure deeper below” said Lekic, an assistant professor of geology at the College Park campus.

Until recently, analyses like the one in the study would have taken up to 19 years of computer time. While studying for his doctorate with the study’s senior author, UC Berkeley Prof. Barbara Romanowicz, Lekic developed a method to more accurately model waveform data while still keeping computer time manageable, which resulted in higher-resolution images of the interaction between the layers of Earth’s mantle.

By refining this method, a research team led by UC Berkeley graduate student Scott French found finger-like channels of low-speed seismic waves flowing about 120 to 220 miles below the sea floor, and stretching out in bands about 700 miles wide and 1,400 miles apart. The researchers also discovered a subtle but important difference in speed: at this depth, seismic waves typically travel about 2.5 to 3 miles per second, but the average seismic velocity in the channels was 4 percent slower. Because higher temperatures slow down seismic waves, the researchers infer that the channels are hotter than the surrounding material.

“We estimate that the slowdown we’re seeing could represent a temperature increase of up to 200 degrees Celsius,” or about 390 degrees Fahrenheit, said French, the study’s study lead author. At these depths, absolute temperatures in the mantle are about 1,300 degrees Celsius, or 2,400 degrees Fahrenheit, the researchers said.

Geophysicists have long theorized that channels akin to those revealed in the computer model exist, and are interacting with the plumes in Earth’s mantle that feed hotspot volcanoes. But the new images reveal for the first time the extent, depth and shape of these channels. And they also show that the fingers align with the motion of the overlying tectonic plate. The researchers hypothesize that these channels may be interacting in complex ways with both the tectonic plates above them and the hot plumes rising from below.

“This global pattern of finger-like structures that we’re seeing, which has not been documented before, appears to reflect interactions between the upwelling plumes and the motion of the overlying plates,” Lekic said. “The deflection of the plumes into these finger-like channels represents an intermediate scale of convection in the mantle, between the large-scale circulation that drives plate motions and the smaller scale plumes, which we are now starting to image.”

“The exact nature of those interactions will need further study,” said French, “but we now have a clearer picture that can help us understand the ‘plumbing’ of Earth’s mantle responsible for hotspot volcano islands like Tahiti, Reunion and Samoa.”

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

Scientists Confirm Existence of Largest Single Volcano On Earth

September 6, 2013

This 3D image of the seafloor shows the size and shape of Tamu Massif, a huge feature in the northern Pacific Ocean, recently confirmed to be the largest single volcano on Earth. (Credit: Image courtesy Will Sager)

A University of Houston (UH) professor led a team of scientists to uncover the largest single volcano yet documented on Earth. Covering an area roughly equivalent to the British Isles or the state of New Mexico, this volcano, dubbed the Tamu Massif, is nearly as big as the giant volcanoes of Mars, placing it among the largest in the Solar System.

William Sager, a professor in the Department of Earth and Atmospheric Sciences at UH, first began studying the volcano about 20 years ago at Texas A&M’s College of Geosciences. Sager and his team’s findings appear in the Sept. 8 issue of Nature Geoscience, the monthly multi-disciplinary journal reflecting disciplines within the geosciences.

Located about 1,000 miles east of Japan, Tamu Massif is the largest feature of Shatsky Rise, an underwater mountain range formed 130 to 145 million years ago by the eruption of several underwater volcanoes. Until now, it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points. By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution research ship, the authors have confirmed that the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the center.

“Tamu Massif is the biggest single shield volcano ever discovered on Earth,” Sager said. “There may be larger volcanoes, because there are bigger igneous features out there such as the Ontong Java Plateau, but we don’t know if these features are one volcano or complexes of volcanoes.”

Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape. It is low and broad, meaning that the erupted lava flows must have traveled long distances compared to most other volcanoes on Earth. The seafloor is dotted with thousands of underwater volcanoes, or seamounts, most of which are small and steep compared to the low, broad expanse of Tamu Massif.

“It’s not high, but very wide, so the flank slopes are very gradual,” Sager said. “In fact, if you were standing on its flank, you would have trouble telling which way is downhill. We know that it is a single immense volcano constructed from massive lava flows that emanated from the center of the volcano to form a broad, shield-like shape. Before now, we didn’t know this because oceanic plateaus are huge features hidden beneath the sea. They have found a good place to hide.”

Tamu Massif covers an area of about 120,000 square miles. By comparison, Hawaii’s Mauna Loa — the largest active volcano on Earth — is approximately 2,000 square miles, or roughly 2 percent the size of Tamu Massif. To find a worthy comparison, one must look skyward to the planet Mars, home to Olympus Mons. That giant volcano, which is visible on a clear night with a good backyard telescope, is only about 25 percent larger by volume than Tamu Massif.

The study relies on two distinct, yet complementary, sources of evidence — core samples collected on Integrated Ocean Drilling Program (IODP) Expedition 324 (Shatsky Rise Formation) in 2009, and seismic reflection data gathered on two separate expeditions of the R/V Marcus G. Langseth in 2010 and 2012. The core samples, drilled from several locations on Tamu Massif, showed that thick lava flows (up to 75 feet thick), characterize this volcano. Seismic data from the R/V Langseth cruises revealed the structure of the volcano, confirming that the lava flows emanated from its summit and flowed hundreds of miles downhill into the adjacent basins.

According to Sager, Tamu Massif is believed to be about 145 million years old, and it became inactive within a few million years after it was formed. Its top lies about 6,500 feet below the ocean surface, while much of its base is believed to be in waters that are almost four miles deep.

“It’s shape is different from any other sub-marine volcano found on Earth, and it’s very possible it can give us some clues about how massive volcanoes can form,” Sager said. “An immense amount of magma came from the center, and this magma had to have come from the Earth’s mantle. So this is important information for geologists trying to understand how the Earth’s interior works.”

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

Between the Water and Fire of Peruvian Volcanoes

September 3, 2013

Illustration of a volcano. (Credit: © EPSL)

Table of Contents

Water and fire coexist under volcanoes to generate “hydrothermal” systems: complex “steam engines” producing white smoke called “fumaroles” that is sometimes observed at the surface. IRD researchers and their partners have just demonstrated why these reservoirs are not always found under the volcanic peaks. For certain structures such as the Ticsani and Ubinas in Peru, where the volcanologists conducted their study, resurgences occur more than 10 km from the top of the dome. Their numerical model shows that the position of the hydrothermal systems depends on regional topography, which may significantly deviate subsurface flows.

Volcanic activity indicators

Most active volcanoes have an internal hydrothermal system, resulting from the infiltration of rainwater, which in contact with the magma, acidifies, heats up, boils and is partly vaporised. Variations in the movement and volume of these liquids or gases reflect changes in volcanic activity. In some eruptions, when magma breaks up in contact with the hydrothermal system, explosive-type eruptions may occur. In the long term, this hydrothermal activity may also contribute to destabilising the volcanic edifice, by altering the rocks. Its position also indicates the permeability of the volcanic rocks. Locating it precisely in the sub-soil helps better estimate the permeability, one of the key parameters of the physical processes at work within volcanoes.

Locating water under the volcano

To understand and better anticipate the unpredictable behaviour of a volcano, it is essential to accurately locate these hydrothermal systems. In fact, they are not necessarily located at the top, as the two Peruvian volcanoes, Ticsani and Ubinas, studied by the research team, demonstrate. Hydrothermal resurgence actually appears more than 10 km downstream from the top of each formation, while only a few events are observed in the hollow of the crater. The researchers firstly measured the soil temperature — up to 37°C at the surface of Ticsani — and hot springs — from 9 to 94°C — as well as the electrical potential created by the movement of fluids in the sub-soil. With this new set of data, they developed a numerical model to explain the asymmetric distribution of hydrothermal fluids.

Major role of the regional landscape

The Ticsani and Ubinas have an atypical profile: peaking at 5,408 and 5,672 metres respectively, they are characterised by a significant difference in altitude between their upstream and downstream sides. Numerical simulations for these two volcanoes show the influence of the regional topography on the position of the hydrothermal system: the considerable altitudinal gradient observed is able to significantly divert the flow of thermal water, shifting groundwater several kilometres in relation to the volcanic cone.

The Ubinas and Ticsani are two of the most active volcanoes in Peru located near the second largest Peruvian agglomeration, Arequipa, which has almost one million inhabitants, and the city of Moquegua. This work helps to locate the water under the volcanoes and to characterise the permanent boiling in their belly. It thus contributes to better monitoring of these threatening giants and better management of eruptive crises.

Note : The above story is based on materials provided by Institut de Recherche pour le Développement (IRD).

Missouri River

September 3, 2013

Table of Contents

The Missouri River is the longest river in North America, longest tributary in the United States and a major waterway of the central United States. Rising in the Rocky Mountains of western Montana, the Missouri flows east and south for 2,341 miles (3,767 km) before entering the Mississippi River north of St. Louis, Missouri. The river takes drainage from a sparsely populated, semi-arid watershed of more than half a million square miles (1,300,000 km2), which includes parts of ten U.S. states and two Canadian provinces. When combined with the lower Mississippi River, it forms the world’s third longest river system.

For over 12,000 years, people have depended on the Missouri and its tributaries as a source of sustenance and transportation. More than ten major groups of Native Americans populated the watershed, most leading a nomadic lifestyle and dependent on enormous buffalo herds that once roamed through the Great Plains. The first Europeans encountered the river in the late seventeenth century, and the region passed through Spanish and French hands before finally becoming part of the United States through the Louisiana Purchase. The Missouri was long believed to be part of the Northwest Passage – a water route from the Atlantic to the Pacific – but when Lewis and Clark became the first to travel the river’s entire length, they confirmed the mythical pathway to be no more than a legend.

The Missouri was one of the main routes for the westward expansion of the United States during the 19th century. The growth of the fur trade in the early 1800s laid much of the groundwork as trappers explored the region and blazed trails. Pioneers headed west en masse beginning in the 1830s, first by covered wagon, then by the growing numbers of steamboats entering service on the river. Former Native American lands in the watershed were taken over by settlers, leading to some of the most longstanding and violent wars against indigenous peoples in American history.

During the 20th century, the Missouri River basin was extensively developed for irrigation, flood control and the generation of hydroelectric power. Fifteen dams impound the main stem of the river, with hundreds more on tributaries. Meanders have been cut and the river channelized to improve navigation, reducing its length by almost 200 miles (320 km) from pre-development times. Although the lower Missouri valley is now a populous and highly productive agricultural and industrial region, heavy development has taken its toll on wildlife and fish populations as well as water quality.

Course

From the Rocky Mountains of Montana and Wyoming, three streams rise to form the headwaters of the Missouri River. The longest begins near Brower’s Spring, 9,100 feet (2,800 m) above sea level, on the southeastern slopes of Mount Jefferson in the Centennial Mountains. Flowing west then north, it runs first in Hell Roaring Creek, then west into the Red Rock; swings northeast to become the Beaverhead, it finally joins with the Big Hole to form the Jefferson. The Firehole River originates at Madison Lake in Wyoming’s Yellowstone National Park and joins with the Gibbon to form the Madison, while the Gallatin River rises out of Gallatin Lake, also in the national park. These two streams then flow north and northwest into Montana.

The Missouri River officially starts at the confluence of the Jefferson and Madison in Missouri Headwaters State Park near Three Forks, Montana, and is joined by the Gallatin a mile (1.6 km) downstream. The Missouri then passes through Canyon Ferry Lake, a reservoir west of the Big Belt Mountains. Issuing from the mountains near Cascade, the river flows northeast to the city of Great Falls, where it drops over the Great Falls of the Missouri, a series of five substantial waterfalls. It then winds east through a scenic region of canyons and badlands known as the Missouri Breaks, receiving the Marias River from the west then widening into the Fort Peck Lake reservoir a few miles above the confluence with the Musselshell River. Farther on, the river passes through the Fort Peck Dam, and immediately downstream, the Milk River joins from the north.

Flowing eastwards through the plains of eastern Montana, the Missouri receives the Poplar River from the north before crossing into North Dakota where the Yellowstone River, its greatest tributary by volume, joins from the southwest. At the confluence, the Yellowstone is actually the larger river. The Missouri then meanders east past Williston and into Lake Sakakawea, the reservoir formed by Garrison Dam. Below the dam the Missouri receives the Knife River from the west and flows south to Bismarck, the capital of North Dakota, where the Heart River joins from the west. It slows into the Lake Oahe reservoir just before the Cannonball River confluence. While it continues south, eventually reaching Oahe Dam in South Dakota, the Grand, Moreau and Cheyenne Rivers all join the Missouri from the west.

The Missouri makes a bend to the southeast as it winds through the Great Plains, receiving the Niobrara River and many smaller tributaries from the southwest. It then proceeds to form the boundary of South Dakota and Nebraska, then after being joined by the James River from the north, forms the Iowa–Nebraska boundary. At Sioux City the Big Sioux River comes in from the north. The Missouri flows south to the city of Omaha where it receives its longest tributary, the Platte River, from the west. Downstream, it begins to define the Nebraska–Missouri border, then flows between Missouri and Kansas. The Missouri swings east at Kansas City, where the Kansas River enters from the west, and so on into north-central Missouri. It passes south of Columbia and receives the Osage and Gasconade Rivers from the south downstream of Jefferson City. The river then rounds the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois.

Geology

The Rocky Mountains of southwestern Montana at the headwaters of the Missouri River first rose in the Laramide Orogeny, a mountain-building episode that occurred from around 70 to 45 million years ago (the end of the Mesozoic through the early Cenozoic). This orogeny uplifted Cretaceous rocks along the western side of the Western Interior Seaway, a vast shallow sea that stretched from the Arctic Ocean to the Gulf of Mexico, and deposited the sediments that now underlie much of the drainage basin of the Missouri River. This Laramide uplift caused the sea to retreat and laid the framework for a vast drainage system of rivers flowing from the Rocky and Appalachian Mountains, the predecessor of the modern-day Mississippi watershed.The Laramide Orogeny is essential to modern Missouri River hydrology, as snow and ice melt from the Rockies provide the majority of the flow in the Missouri and its tributaries.

The Missouri and many of its tributaries cross the Great Plains, flowing over or cutting into the Ogallala Group and older mid-Cenozoic sedimentary rocks. The lowest major Cenozoic unit, the White River Formation, was deposited between roughly 35 and 29 million years ago and consists of claystone, sandstone, limestone, and conglomerate. Channel sandstones and finer-grained overbank deposits of the fluvial Arikaree Group were deposited between 29 and 19 million years ago. The Miocene-age Ogallala and the slightly younger Pliocene-age Broadwater Formation deposited atop the Arikaree Group, and are formed from material eroded off of the Rocky Mountains during a time of increased generation of topographic relief; these formations stretch from the Rocky Mountains nearly to the Iowa border and give the Great Plains much of their gentle but persistent eastward tilt, and also constitute a major aquifer.

Immediately before the Quaternary Ice Age, the Missouri River was likely split into three segments: an upper portion that drained northwards into Hudson Bay, and middle and lower sections that flowed eastward down the regional slope. As the Earth plunged into the Ice Age, a pre-Illinoian (or possibly the Illinoian) glaciation diverted the Missouri River southeastwards towards its present confluence with the Mississippi and caused it to integrate into a single river system that cuts across the regional slope. In western Montana, the Missouri River is thought to have once flowed north then east around the Bear Paw Mountains. Sapphires are found in some spots along the river in western Montana. Advances of the continental ice sheets diverted the river and its tributaries, causing them to pool up into large temporary lakes such as Glacial Lakes Great Falls, Musselshell and others. As the lakes rose, the water in them often spilled across adjacent local drainage divides, creating now-abandoned channels and coulees including the Shonkin Sag, 100 miles (160 km) long. When the glaciers retreated, the Missouri flowed in a new course along the south side of the Bearpaws, and the lower part of the Milk River tributary took over the original main channel.

The Missouri’s nickname, the “Big Muddy”, was inspired by its enormous loads of sediment or silt – some of the largest of any North American river. In its pre-development state, the river transported some 175–320 million short tons (193–290 million t) per year. The construction of dams and levees has drastically reduced this to 20–25 million short tons (18–23 million t) in the present day. Much of this sediment is derived from the river’s floodplain, also called the meander belt; every time the river changed course, it would erode tons of soil and rocks from its banks. However, damming and channeling the river has kept it from reaching its natural sediment sources along most of its course. Reservoirs along the Missouri trap roughly 36.4 million short tons (32.9 million t) of sediment each year. Despite this, the river still transports more than half the total silt that empties into the Gulf of Mexico; the Mississippi River Delta, formed by sediment deposits at the mouth of the Mississippi, constitutes a majority of sediments carried by the Missouri.

The Missouri River in Upper Missouri Breaks National Monument, Montana, at the confluence with Cow Creek

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

Research suggests terror bird’s beak was worse than its bite

August 30, 2013

This is a Gastornis geiselensis sketch of the generel skeleton in lateral view after MATTHEW and GRANGER (1917) with the tarsometatarsus modified correctly adapted from HELLMUND (2013). The size of the skeleton is about 2 m.Credit: Tuetkin

It’s a fiercely debated question amongst palaeontologists: was the giant ‘terror bird’, which lived in Europe between 55 to 40 million years ago, really a terrifying predator or just a gentle herbivore?

New research presented at the Goldschmidt conference in Florence today (Thursday 29th August) may finally provide an answer. A team of German researchers has studied fossilised remains of terror birds from a former open-cast brown coal mine in the Geiseltal (Saxony-Anhalt, Germany) and their findings indicate the creature was most likely not a meat eater.

The terror bird – also known as Gastornis – was a flightless bird up to two metres in height with an enormous, ferocious beak. Based upon its size and ominous appearance, scientists have long assumed that it was a ruthless carnivore.

“The terror bird was thought to have used its huge beak to grab and break the neck of its prey, which is supported by biomechanical modelling of its bite force,” says Dr Thomas Tütken, from the University of Bonn. “It lived after the dinosaurs became extinct and at a time when mammals were at an early stage of evolution and relatively small; thus, the terror bird was though to have been a top predator at that time on land.”

Recent research has cast some doubt on its diet, however. Palaeontologists in the United States found footprints believed to belong to the American cousin of Gastornis, and these do not show the imprints of sharp claws, used to grapple prey, that might be expected of a raptor. Also, the bird’s sheer size and inability to move fast has made some believe it couldn’t have predated on early mammals – though others claim it might have ambushed them. But, without conclusive findings either way, the dietary inclinations of Gastornis remain a mystery.

Dr Tütken and his colleagues Dr Meinolf Hellmund, Dr Stephen Galer and Petra Held have taken a new geochemical approach to determine the diet of Gastornis. By analysing the calcium isotope composition in fossilised bones, they have been able to identify what proportion of a creature’s diet was plant or animal and, on that basis, their position in the food chain of the local ecosystem. This depends on the calcium isotopic composition becoming “lighter” as it passes through the food chain. They tested the method first with herbivorous and carnivorous dinosaurs – including top predator T-Rex – as well as mammals living today, before applying it to terror bird bones held in the Geiseltal collection at Martin-Luther University in Halle.

Their results show that the calcium isotope compositions of terror bird bones are similar to those of herbivorous mammals and dinosaurs and not carnivorous ones. Before the debate is finally closed, however, the researchers want to cross check their data using other fossil assemblages to be completely sure.

“Tooth enamel preserves original geochemical signatures much better than bone, but since Gastornis didn’t have any teeth, we’ve had to work with their bones to do our calcium isotope assay,” explains Dr Tütken. “Because calcium is a major proportion of bone – around 40% by weight – its composition is unlikely to have been affected much by fossilisation. However, we want to be absolutely confident in our findings by analysing known herbivores and carnivores using fossilised bone from the same site and the same time period. This will give us an appropriate reference frame for the terror bird values.”

Note : The above story is based on materials provided by European Association of Geochemistry, via EurekAlert!, a service of AAAS.

Hidden Shell Middens Reveal Ancient Human Presence in Bolivian Amazon

August 29, 2013

Details of recovered burnt earth, shells and bone remains from excavations at SM1. A) Thin section from Unit VI; aragonitic and micritic shell fragments cemented together; a bone is visible in the upper left corner (cross polarized light, XPL); b) Pomacea shells found at a depth of 110 cm; c) Impact scar between refitted fragments of a Blastocerus dichotomus tibia found at 160 cm. Mineral dendrites covering the edges of bones and surface damage indicate a percussive blow; d) Mandibular fragment of Mazama sp. found at a depth of 70–75 cm; e) Fragment of burnt earth found at a depth of 140 cm with incised parallel lines, probably culturally-modified; f) Units IV and V as observed in the excavations; Unit V is a layer of well cemented shells surrounded by loose fragments that form Unit IV. (Credit: Image courtesy of Public Library of Science)

Previously unknown archeological sites in forest islands reveal human presence in the western Amazon as early as 10,000 years ago, according to research published August 28 in the open access journal PLOS ONE by Umberto Lombardo from the University of Bern, Switzerland and colleagues from other institutions.

The study focuses on a region in the Bolivian Amazon thought to be rarely occupied by pre-agricultural communities due to unfavorable environmental conditions. Hundreds of ‘forest islands’- small forested mounds of earth- are found throughout the region, their origins attributed to termites, erosion or ancient human activity. In this study, the authors report that three of these islands are shell middens, mounds of seashells left by settlers in the early Holocene period, approximately 10,400 years ago.

Samples of soil from these three mounds revealed a dense accumulation of freshwater snail shells, animal bones and charcoal forming the middens. The mounds appear to have formed in two phases: an older layer composed primarily of snail shells, and an overlying layer composed of organic matter containing pottery, bone tools and human bones. The two are separated by a thin layer rich in pieces of burnt clay and earth, and the uppermost layer of deposits was also seen to contain occasional fragments of earthenware pottery.

Radiocarbon analysis of two middens indicates that humans settled in this region during the early Holocene, approximately 10,400 years ago, and shells and other artefacts built up into mounds over an approximately 6,000 year period of human use. The sites may have been abandoned as climate shifted towards wetter conditions later. Lombardo adds, “We have discovered the oldest archaeological sites in western and southern Amazonia. These sites allow us to reconstruct 10,000 years of human-environment interactions in the Bolivian Amazon.”

Note : The above story is based on materials provided by Public Library of Science.

NASA Data Reveals Mega-Canyon Under Greenland Ice Sheet

August 29, 2013

Hidden for all of human history, a 460 mile long canyon has been discovered below Greenland’s ice sheet. Using radar data from NASA’s Operation IceBridg, scientists found the canyon runs from near the center of the island northward to the fjord of the Petermann Glacier. (Credit: Image courtesy of NASA)

Data from a NASA airborne science mission reveals evidence of a large and previously unknown canyon hidden under a mile of Greenland ice.

The canyon has the characteristics of a winding river channel and is at least 460 miles (750 kilometers) long, making it longer than the Grand Canyon. In some places, it is as deep as 2,600 feet (800 meters), on scale with segments of the Grand Canyon. This immense feature is thought to predate the ice sheet that has covered Greenland for the last few million years.

“One might assume that the landscape of the Earth has been fully explored and mapped,” said Jonathan Bamber, professor of physical geography at the University of Bristol in the United Kingdom, and lead author of the study. “Our research shows there’s still a lot left to discover.”

Bamber’s team published its findings Thursday in the journal Science.

The scientists used thousands of miles of airborne radar data, collected by NASA and researchers from the United Kingdom and Germany over several decades, to piece together the landscape lying beneath the Greenland ice sheet.

A large portion of this data was collected from 2009 through 2012 by NASA’s Operation IceBridge, an airborne science campaign that studies polar ice. One of IceBridge’s scientific instruments, the Multichannel Coherent Radar Depth Sounder, can see through vast layers of ice to measure its thickness and the shape of bedrock below.

In their analysis of the radar data, the team discovered a continuous bedrock canyon that extends from almost the center of the island and ends beneath the Petermann Glacier fjord in northern Greenland.

At certain frequencies, radio waves can travel through the ice and bounce off the bedrock underneath. The amount of times the radio waves took to bounce back helped researchers determine the depth of the canyon. The longer it took, the deeper the bedrock feature.

“Two things helped lead to this discovery,” said Michael Studinger, IceBridge project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “It was the enormous amount of data collected by IceBridge and the work of combining it with other datasets into a Greenland-wide compilation of all existing data that makes this feature appear in front of our eyes.”

The researchers believe the canyon plays an important role in transporting sub-glacial meltwater from the interior of Greenland to the edge of the ice sheet into the ocean. Evidence suggests that before the presence of the ice sheet, as much as 4 million years ago, water flowed in the canyon from the interior to the coast and was a major river system.

“It is quite remarkable that a channel the size of the Grand Canyon is discovered in the 21st century below the Greenland ice sheet,” said Studinger. “It shows how little we still know about the bedrock below large continental ice sheets.”

The IceBridge campaign will return to Greenland in March 2014 to continue collecting data on land and sea ice in the Arctic using a suite of instruments that includes ice-penetrating radar.

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

Earthquakes and Tectonics in Pamir Tien Shan

August 27, 2013

Cross section through the Earth’s crust and mantle in the Pamir. The Pamir mountains are located in the northernmost part of the India-Eurasia collision zone. In this collision zone occur both shallow and deep earthquakes (depicted as white dots). The deep earthquakes are caused by the subduction of lower Eurasian crust. Black triangles: location of the linear seismometer array. (Credit: GFZ)

Earthquake damage to buildings is mainly due to the existing shear waves which transfer their energy during an earthquake to the houses. These shear waves are significantly influenced by the underground and the topography of the surrounding area. Detailed knowledge of the landform and the near-surface underground structure is, therefore, an important prerequisite for a local seismic hazard assessment and for the evaluation of the ground-effect, which can strongly modify and increase local ground motion.

As described in the latest issue of Geophysical Journal International, a team of scientists from the GFZ German Research Center for Geosciences could show that it is possible to map complex shear wave velocity structures almost in real time by means of a newly developed tomgraphic approach.

The method is based on ambient seismic noise recordings and analyses. “We use small, hardly noticeable amplitude ground motions as well as anthropogenic ground vibrations,” Marco Pilz, a scientist at GFZ, explains. “With the help of these small signals we can obtain detailed images of the shallow seismic velocity structure.” In particular, images and velocity changes in the underground due to earthquakes and landslides can be obtained in almost real time.

“What is new about our method is the direct calculation of the shear wave velocity. Moreover, we are working on a local, small-scale level — compared to many other studies,” Marco Pilz continues.

This method has already been successfully applied: Many regions of Central Asia are threatened by landslides. Since the shear wave velocity usually drops significantly before a landslide slip this technique offers the chance to monitor changes in landslide prone areas almost in real time.

Further application can be used in earthquake research. The authors were able to map the detailed structure of a section of the Issyk-Ata fault, Kyrgyzstan, which runs along the southern border of the capital city, Bishkek, with a population of approx. 900.000 inhabitants. They showed that close to the surface of the mapped section a splitting into two different small fault branches can be observed. This can influence the pace of expansion or also an eventual halting of the propagation on the main fault.

Central Asia is extensively seismically endangered; the accompanying processes and risks are investigated by the Central-Asian Institute of Applied Geosciences (CAIAG) in Bishkek, a joint institution established by the GFZ and the Kyrgyz government.

Why do these earthquakes occur?

The Pamir and Tien Shan are the result of the crash of two continental plates: the collision of India and Eurasia causes the high mountain ranges. This process is still ongoing today and causes breaking of the Earths crust, of which earthquakes are the consequence.

A second group of GFZ-scientists has investigated together with colleagues from Tajikistan and CAIAG the tectonic process of collision in this region. They were, for the first time, able to image continental crust descending into the Earth’s mantle. In the scientific journal Earth and Planetary Sciences Letters the scientists report that this subduction of continental crust has, to date, never been directly observed. To make their images, the scientists applied a special seismological method (so-called receiver function-analysis) on seismograms that had been collected in a two years long field experiment in the Tien Shan-Pamir-Hindu Kush area. Here, the collision of the Indian and Eurasian plates presents an extreme dimension.

“These extreme conditions cause the Eurasian lower crust to subduct into the Earth’s mantle,” explains Felix Schneider from the GFZ German Research Centre for Geosciences.” Such a subduction can normally be observed during the collision of ocean crust with continental crust, as the ocean floors are heavier than continental rock.”

Findings at the surface of metamorphic rocks that must have arisen from ultra-high pressures deep in the Earth’s mantle also provide evidence for subduction of continental crust in the Pamir region. Furthermore, the question arises, how the occurrence of numerous earthquakes at unusual depths of down to 300 km in the upper mantel can be explained. Through the observation of the subducting part of the Eurasian lower crust, this puzzle could, however, be solved.

Note : The above story is based on materials provided by Helmholtz Centre Potsdam – GFZ German Research Centre for Geosciences.

Supervolcanic Ash Can Turn to Lava Miles from Eruption

August 27, 2013

Evidence of flowing lava hardened into rock found in Idaho several miles away from the site of an 8 million year old supervolcano eruption at Yellowstone. (Credit: Graham Andrews, assistant professor at California State University Bakersfield.)

Supervolcanoes, such as the one sitting dormant under Yellowstone National Park, are capable of producing eruptions thousands of times more powerful than normal volcanic eruptions. While they only happen every several thousand years, these eruptions have the potential to kill millions of people and animals due to the massive amount of heat and ash they release into the atmosphere. Now, researchers at the University of Missouri have shown that the ash produced by supervolcanoes can be so hot that it has the ability to turn back into lava once it hits the ground tens of miles away from the original eruption.

Following a volcanic eruption, lava typically flows directly from the site of the eruption until it cools enough that it hardens in place. However, researchers found evidence of an ancient lava flow tens of miles away from a supervolcano eruption near Yellowstone that occurred around 8 million years ago. Previously, Graham Andrews, an assistant professor at California State University Bakersfield, found that this lava flow was made of ash ejected during the eruption. Following Andrew’s discovery, Alan Whittington, an associate professor in the University of Missouri department of geological sciences in the College of Arts and Science, along with lead author Genevieve Robert and Jiyang Ye, both doctoral students in the geological sciences department, determined how this was possible.

“During a supervolcano eruption, pyroclastic flows, which are giant clouds of very hot ash and rock, travel away from the volcano at typically a hundred miles an hour,” Robert said. “We determined the ash must have been exceptionally hot so that it could actually turn into lava and flow before it eventually cooled.”

Because the ash should have cooled too much in the air to turn into lava right as it landed, the researchers believe the phenomenon was made possible by a process known as “viscous heating.” Viscosity is the degree to which a liquid resists flow. The higher the viscosity, the less the substance can flow. For example, water has a very low viscosity, so it flows very easily, while molasses has a higher viscosity and flows much slower. Whittington likens the process of viscous heating to stirring a pot of molasses.

“It is very hard to stir a pot of molasses and you have to use a lot of energy and strength to move your spoon around the pot,” Whittington said. “However, once you get the pot stirring, the energy you are using to move the spoon is transferred into the molasses, which actually heats up a little bit. This is viscous heating. So when you think about how fast the hot ash is traveling after a massive supervolcano eruption, once it hits the ground that energy is turned into heat, much like the energy from the spoon heating up the molasses. This extra heat created by viscous heating is enough to cause the ash to weld together and actually begin flowing as lava.”

The volcanic ash from this eruption has to be at least 1,500 degrees Fahrenheit to turn into lava; however, since the ash should have lost some of that heat in the air, the researchers believe viscous heating accounted for 200 to 400 degrees Fahrenheit of additional heating to turn the ash into lava.

Robert, Andrews, Ye, and Whittington’s paper was published in Geology. The National Science Foundation funded this research through a CAREER award to Whittington.

Note : The above story is based on materials provided by University of Missouri-Columbia.

Geologic study suggests Earth’s tectonic activity peaked 1.1 billion years ago

August 27, 2013

A pair of Australian researchers studying rock samples has found evidence to suggest that the Earth’s tectonic plate activity peaked approximately 1.1 billion years ago. In their paper published in the journal Geology, Martin Van Kranendonk and Christopher Kirkland describe the results of their analysis of a multitude of rock samples from various sites around the world.

Scientists agree that the Earth’s tectonic plates have been shifting for at least 3 billion years, but no one really knows whether such shifting has been getting more or less active. In this new effort Kranendonk and Kirkland undertook an exhaustive study of rock samples to learn more.

The two first looked at 3200 samples of rocks collected by various researchers over the years, taken from various points around the world. Specifically, they were looking for the amount of zirconium and thorium in them—both have been found to be more common in rocks that were formed during tectonically active periods. Next they looked at an additional 1200 rock samples, this time looking for oxygen isotopes, which are also known to be more common in rocks created during times of high tectonic activity.

In analyzing the data obtained from studying the rocks, the researchers found evidence that suggests that tectonic activity increased from a time approximately 3 billion years ago. That activity continued to increase, they say, for 2 billion years, peaking around 1.1 billion years ago—a time during which all of the continents had merged into one supercontinent called Rodinia. Since that time, they note, it appears that tectonic activity has been slowing. This suggests that the planet has a lifespan.

The rocks can’t offer any evidence to explain why there was an increase in activity or why it has been slowing after peaking, but the researchers have a theory—they believe that prior to the increase in tectonic activity, tectonic plates the world over became thicker, and likely larger. This meant collisions between plates would have been far more violent than before. As the Earth cooled off, the plates would have moved slower causing less activity overall. These new findings also suggest that at some point the Earth’s plates will stop moving altogether—though how long that might take is still a mystery.

More information: Orogenic climax of Earth: The 1.2–1.1 Ga Grenvillian superevent, Geology, First published online April 29, 2013, doi: 10.1130/G34243.1

Abstract
The rate of growth of the continental crust is controversial. We present an evaluation of time-constrained analyses of oxygen isotopes in zircon grains and incompatible element (Zr, Th) concentrations in magmatic rocks to test for variations in the degree of crustal recycling through geological time. The data indicate a rise in these geochemical proxies from ca. 3.0 Ga to a statistically significant peak at 1.2–1.1 Ga during the amalgamation of supercontinent Rodinia, and a decrease thereafter. When combined with other geological and geophysical observations, the data are interpreted as a consequence of an unprecedented level of crustal recycling and sediment subduction during Rodinia assembly, arising from a “Goldilocks” (i.e., just right) combination of larger, thicker plates on a warmer Earth with more rapid continental drift relative to modern Earth. The subsequent decrease in δ18O, Zr, and Th measurements is interpreted to reflect decreasing drift rates on a cooling Earth.

Note : The above story is based on materials provided by Newscientist

Mapping the planet’s ups and downs

August 26, 2013

Maryhill in Glasgow has never looked quite as spectacular as this 3D model

Researchers at the University of Glasgow are using a new technique known as interferometric synthetic aperture radar (InSAR) to predict natural disasters around the world and manage their impact.

InSAR scans the Earth from space looking for points that are prone to surface changes and monitor their movement over time. It is hoped that the technology will play a considerable role in predicting where natural disasters such as volcanic eruptions and landslides may take place and help save lives.

Led by Dr Zhenhong Li at the University of Glasgow’s School of Geographical and Earth Sciences, the team are looking at the surface of our planet from space and using satellites to track changes in the Earth’s surface that may otherwise be unnoticeable.

PhD student, Andrew Singleton, said: “We take one radar image taken at a certain time, and then a few days

“Obviously that has many applications for earthquakes and volcanoes. But my particular project focuses on landslide movements.”

On the ground the full extent may be masked by vegetation. But from orbit InSAR lays it bare, and the Glasgow team’s modelling techniques mean authorities can be forewarned, limiting the impact of some natural disasters.

Researchers in Glasgow can spot landslips near China’s Yangtze river

Dr Li has also applied the techniques to one of the unexpected side effects of a growing Chinese economy: subsidence. He has measured the effects of coal mining, and of the unchecked extraction of groundwater.

That has seen the water table fall by as much as three metres (10ft) in some parts of north-eastern China – and some buildings fall into sinkholes.

He has also been able to quickly assess the effects of natural disasters like the Yushu earthquake which killed thousands of people in north-western China in 2010. Within hours of receiving radar data from the disaster area he was able to map the extent of the rupture in the Earth’s surface.

“It only took me – a single researcher – two hours to produce these in the office,” he says. “But it took our Chinese colleagues two weeks in the field to collect all the measurements.”

And when they did that work on the ground, they found Dr Li’s measurements from orbit had been accurate to within 10cm.

later we take a second radar image. Between those two time periods we can detect elevation changes in the Earth’s surface.

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

Earlier Peak for Spain’s Glaciers

August 26, 2013

Willenbring (upper right) takes samples to date a boulder in central Spain’s Bejár mountain range. (Credit: Image courtesy of University of Pennsylvania)

The last glacial maximum was a time when Earth’s far northern and far southern latitudes were largely covered in ice sheets and sea levels were low. Over much of the planet, glaciers were at their greatest extent roughly 20,000 years ago. But according to a study headed by University of Pennsylvania geologist Jane Willenbring, that wasn’t true in at least one part of southern Europe. Due to local effects of temperature and precipitation, the local glacial maximum occurred considerably earlier, around 26,000 years ago.
The finding sheds new light on how regional climate has varied over time, providing information that could lead to more-accurate global climate models, which predict what changes Earth will experience in the future.

Willenbring, an assistant professor in Penn’s Department of Earth and Environmental Science in the School of Arts and Sciences, teamed with researchers from Spain, the United Kingdom, China and the United States to pursue this study of the ancient glaciers of southern Europe.

“We wanted to unravel why and when glaciers grow and shrink,” Willenbring said.

In the study site in central Spain, it is relatively straightforward to discern the size of ancient glaciers, because the ice carried and dropped boulders at the margin. Thus a ring of boulders marks the edge of the old glacier.

It is not as easy to determine what caused the glacier to grow, however. Glaciers need both moisture and cold temperatures to expand. Studying the boulders that rim the ancient glaciers alone cannot distinguish these contributions. Caves, however, provide a way to differentiate the two factors. Stalagmites and stalactites — the stony projections that grow from the cave floor and ceiling, respectively — carry a record of precipitation because they grow as a result of dripping water.

“If you add the cave data to the data from the glaciers, it gives you a neat way of figuring out whether it was cold temperatures or higher precipitation that drove the glacier growth at the time,” Willenbring said.

The researchers conducted the study in three of Spain’s mountain ranges: the Bejár, Gredos and Guadarrama. The nearby Eagle Cave allowed them to obtain indirect precipitation data.

To ascertain the age of the boulders strewn by the glaciers and thus come up with a date when glaciers were at their greatest extent, Willenbring and colleagues used a technique known as cosmogenic nuclide exposure dating, which measures the chemical residue of supernova explosions. They also used standard radiometric techniques to date stalagmites from Eagle Cave, which gave them information about fluxes in precipitation during the time the glaciers covered the land.

“Previously, people believe the last glacial maximum was somewhere in the range of 19-23,000 years ago,” Willenbring said. “Our chronology indicates that’s more in the range of 25-29,000 years ago in Spain.”

The geologists found that, although temperatures were cool in the range of 19,000-23,000 years ago, conditions were also relatively dry, so the glaciers did not regain the size they had obtained several thousand years earlier, when rain and snowfall totals were higher. They reported their findings in the journal Scientific Reports.

Given the revised timeline in this region, Willenbring and colleagues determined that the increased precipitation resulted from changes in the intensity of the sun’s radiation on the Earth, which is based on the planet’s tilt in orbit. Such changes can impact patterns of wind, temperature and storms.

“That probably means there was a southward shift of the North Atlantic Polar Front, which caused storm tracks to move south, too,” Willenbring said. “Also, at this time there was a nice warm source of precipitation, unlike before and after when the ocean was colder.”

Willenbring noted that the new date for the glacier maximum in the Mediterranean region, which is several thousands of years earlier than the date the maximum was reached in central Europe, will help provide more context for creating accurate global climate models.

“It’s important for global climate models to be able to test under what conditions precipitation changes and when sources for that precipitation change,” she said. “That’s particularly true in some of these arid regions, like the American Southwest and the Mediterranean.”

When glaciers were peaking in the Mediterranean around 26,000 years ago, the American Southwest was experiencing similar conditions. Areas that are now desert were moist. Large lakes abounded, including Lake Bonneville, which covered much of modern-day Utah. The state’s Great Salt Lake is what remains.

“Lakes in this area were really high for 5,000-10,000 years, and the cause for that has always been a mystery,” Willenbring said. “By looking at what was happening in the Mediterranean, we might eventually be able to say something about the conditions that led to these lakes in the Southwest, too.”

This research was supported by the Ministerio de Ciencia e Innovación and the Junta de Comunidades de Castilla-La Mancha.

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

Earlier Peak for Spain’s Glaciers

August 26, 2013