Chemical Formula: Cu2O Locality: Commonly in the copper deposits of SW USA and in Chile. Name Origin: From the Latin, cuprum, meaning copper. Chalcotrichite from the Greek, meaning “hairy copper.”
Cuprite is an oxide mineral composed of copper(I) oxide Cu2O, and is a minor ore of copper.
Its dark crystals with red internal reflections are in the isometric system hexoctahedral class, appearing as cubic, octahedral, or dodecahedral forms, or in combinations. Penetration twins frequently occur. In spite of its nice color it is rarely used for jewelry because of its low Mohs hardness of 3.5 to 4. It has a relatively high specific gravity of 6.1, imperfect cleavage and a brittle to conchoidal fracture. The luster is sub-metallic to brilliant adamantine. The “chalcotrichite” variety typically shows greatly elongated (parallel to [001]) capillary or needle like crystals forms.
It is a secondary mineral which forms in the oxidized zone of copper sulfide deposits. It frequently occurs in association with native copper, azurite, chrysocolla, malachite, tenorite and a variety of iron oxide minerals. It is known as ruby copper due to its distinctive red color.
Cuprite was first described in 1845 and the name derives from the Latin cuprum for its copper content.
Cuprite is found in the Ural Mountains, Altai Mountains, and Sardinia, and in more isolated locations in Cornwall, France, Arizona, Chile, Bolivia, and Namibia.
This artist’s impression depicts the magma chamber of a supervolcano with partially molten magma at the top. The pressure from the buoyancy is sufficient to initiate cracks in the Earth’s crust in which the magma can penetrate. (Credit: ESRF/Nigel Hawtin)
Scientists have reproduced the conditions inside the magma chamber of a supervolcano to understand what it takes to trigger its explosion. These rare events represent the biggest natural catastrophes on Earth except for the impact of giant meteorites. Using synchrotron X-rays, the scientists established that supervolcano eruptions may occur spontaneously, driven only by magma pressure without the need for an external trigger. The results are published in Nature Geosciences.
The team was led by Wim Malfait and Carmen Sanchez-Valle of ETH Zurich (Switzerland) and comprised scientists from the Paul Scherrer Institute in Villigen (Switzerland), Okayama University (Japan), the Laboratory of Geology of CNRS, Université Lyon 1 and ENS Lyon (France) and the European Synchrotron (ESRF) in Grenoble (France).
A well-known supervolcano eruption occurred 600,000 years ago in Wyoming in the United States, creating a huge crater called a caldera, in the centre of what today is Yellowstone National Park. When the volcano exploded, it ejected more than 1000 km3 of ash and lava into the atmosphere, 100 times more than Mt Pinatubo in the Philippines did in 1992. Big volcanic eruptions have a major impact on the global climate. The Mt Pinatubo eruption decreased the global temperature by 0.4 degrees Celsius for a few months. The predictions for a super volcano are a fall in temperatures by 10 degrees Celsius for 10 years.
According to a 2005 report by the Geological Society of London, “Even science fiction cannot produce a credible mechanism for averting a super-eruption. We can, however, work to better understand the mechanisms involved in super-eruptions, with the goal of being able to predict them ahead of time and provide a warning for society. Preparedness is the key to mitigation of the disastrous effects of a super-eruption.”
The mechanisms that trigger supervolcano eruptions have remained elusive to date. The main reason is that the processes inside a supervolcano are different from those in conventional volcanoes like Mt. Pinatubo which are better understood. A supervolcano possesses a much larger magma chamber and it is always located in an area where the heat flow from the interior of Earth to the surface is very high. As a consequence, the magma chamber is very large and hot but also plastic: its shape changes as a function of the pressure when it gradually fills with hot magma. This plasticity allows the pressure to dissipate more efficiently than in a normal volcano whose magma chamber is more rigid. Supervolcanoes therefore do not erupt very often.
So what changes in the lead up to an eruption? Wim Malfait explains: “The driving force is an additional pressure which is caused by the different densities of solid rock and liquid magma. It is comparable to a football filled with air under water, which is forced upwards by the denser water around it.” Whether this additional pressure alone could eventually become sufficiently high to crack Earth’s crust, leading to a violent eruption, or whether an external energy source like an Earthquake is required has only now been answered.
Whilst it is virtually impossible to drill a hole into the magma chamber of a supervolcano given the depth at which these chambers are buried, one can simulate these extreme conditions in the laboratory. “The synchrotron X-rays at the ESRF can then be used to probe the state — liquid or solid — and the change in density when magma crystallises into rock” says Mohamed Mezouar, scientist at the ESRF and member of the team. Jean-Philippe Perrillat from the Laboratory of Geology of CNRS, Université Lyon 1 and ENS Lyon adds: “Temperatures of up to 1700 degrees and pressures of up to 36,000 atmospheres can be reached inside the so-called Paris-Edinburgh press, where speck-sized rock samples are placed between the tips of two tungsten carbide anvils and then heated with a resistive furnace. This special set-up was used to accurately determine the density of the liquid magma over a wide range of pressures and temperatures.”
Magma often includes water, which as vapour adds additional pressure. The scientists also determined magma densities as a function of water content.
The results of their measurements showed that the pressure resulting from the differences in density between solid and liquid magma rock is sufficient in itself to crack more than ten kilometres of Earth’s crust above the magma chamber. Carmen Sanchez-Valle concludes: “Our research has shown that the pressure is actually large enough for Earth’s crust to break. The magma penetrating into the cracks will eventually reach Earth’s surface, even in the absence of water or carbon dioxide bubbles in the magma. As it rises to the surface, the magma will expand violently, which is the well known origin of a volcanic explosion.”
Note : The above story is based on materials provided by CNRS.
The April 10, 2013, landslide at Rio Tinto-Kennecott Utah Copper’s Bingham Canyon mine contains enough debris to bury New York City’s Central Park 66 feet deep, according to a new University of Utah study. The slide happened in the form of two rock avalanches 95 minutes apart. The first rock avalanche included grayer bedrock material seen around the margins of the lower half of the slide. The second rock avalanche is orange in color, both from bedrock and from waste rock from mining. The new study found the landslide triggered 16 small quakes. Such triggering has not been noted previously. The slide likely was the largest nonvolcanic landslide in North America’s modern history. Credit: Kennecott Utah Copper.
Last year’s gigantic landslide at a Utah copper mine probably was the biggest nonvolcanic slide in North America’s modern history, and included two rock avalanches that happened 90 minutes apart and surprisingly triggered 16 small earthquakes, University of Utah scientists discovered.
The landslide – which moved at an average of almost 70 mph and reached estimated speeds of at least 100 mph – left a deposit so large it “would cover New York’s Central Park with about 20 meters (66 feet) of debris,” the researchers report in the January 2014 cover study in the Geological Society of America magazine GSA Today.
While earthquakes regularly trigger landslides, the gigantic landslide the night of April 10, 2013, is the first known to have triggered quakes. The slide occurred in the form of two huge rock avalanches at 9:30 p.m. and 11:05 p.m. MDT at Rio Tinto-Kennecott Utah Copper’s open-pit Bingham Canyon Mine, 20 miles southwest of downtown Salt Lake City. Each rock avalanche lasted about 90 seconds.
While the slides were not quakes, they were measured by seismic scales as having magnitudes up to 5.1 and 4.9, respectively. The subsequent real quakes were smaller.
Kennecott officials closely monitor movements in the 107-year-old mine – which produces 25 percent of the copper used in the United States – and they recognized signs of increasing instability in the months before the slide, closing and removing a visitor center on the south edge of the 2.8-mile-wide, 3,182-foot-deep open pit, which the company claims is the world’s largest manmade excavation.
Landslides – including those at open-pit mines but excluding quake-triggered slides – killed more than 32,000 people during 2004-2011, the researchers say. But no one was hurt or died in the Bingham Canyon slide. The slide damaged or destroyed 14 haul trucks and three shovels and closed the mine’s main access ramp until November.
“This is really a geotechnical monitoring success story,” says the new study’s first author, Kris Pankow, associate director of the University of Utah Seismograph Stations and a research associate professor of geology and geophysics. “No one was killed, and yet now we have this rich dataset to learn more about landslides.”
There have been much bigger human-caused landslides on other continents, and much bigger prehistoric slides in North America, including one about five times larger than Bingham Canyon some 8,000 years ago at the mouth of Utah’s Zion Canyon.
But the Bingham Canyon Mine slide “is probably the largest nonvolcanic landslide in modern North American history,” said study co-author Jeff Moore, an assistant professor of geology and geophysics at the University of Utah.
There have been numerous larger, mostly prehistoric slides – some hundreds of times larger. Even the landslide portion of the 1980 Mount St. Helens eruption was 57 times larger than the Bingham Canyon slide.
News reports initially put the landslide cost at close to $1 billion, but that may end up lower because Kennecott has gotten the mine back in operation faster than expected.
Until now, the most expensive U.S. landslide was the 1983 Thistle slide in Utah, which cost an estimated $460 million to $940 million because the town of Thistle was abandoned, train tracks and highways were relocated and a drainage tunnel built.
Pankow and Moore conducted the study with several colleagues from the university’s College of Mines and Earth Sciences: J. Mark Hale, an information specialist at the Seismograph Stations; Keith Koper, director of the Seismograph Stations; Tex Kubacki, a graduate student in mining engineering; Katherine Whidden, a research seismologist; and Michael K. McCarter, professor of mining engineering.
The study was funded by state of Utah support of the University of Utah Seismograph Stations and by the U.S. Geological Survey.
The University of Utah researchers say the Bingham Canyon slide was among the best-recorded in history, making it a treasure trove of data for studying slides.
Kennecott has estimated the landslide weighed 165 million tons. The new study estimated the slide came from a volume of rock roughly 55 million cubic meters (1.9 billion cubic feet). Rock in a landslide breaks up and expands, so Moore estimated the landslide deposit had a volume of 65 million cubic meters (2.3 billion cubic feet).
Moore calculated that not only would bury Central Park 66 feet deep, but also is equivalent to the amount of material in 21 of Egypt’s great pyramids of Giza.
The landslide’s two rock avalanches were not earthquakes but, like mine collapses and nuclear explosions, they were recorded on seismographs and had magnitudes that were calculated on three different scales:
The first slide at 9:30 p.m. MDT measured 5.1 in surface-wave magnitude, 2.5 in local or Richter magnitude, and 4.2 in duration or “coda” magnitude.
The second slide at 11:05 p.m. MDT measured 4.9 in surface-wave magnitude, 2.4 in Richter magnitude and 3.5 in coda magnitude.
Pankow says the larger magnitudes more accurately reflect the energy released by the rock avalanches, but the smaller Richter magnitudes better reflect what people felt – or didn’t feel, since the Seismograph Stations didn’t receive any such reports. That’s because the larger surface-wave magnitudes record low-frequency energy, while Richter and coda magnitudes are based on high-frequency seismic waves that people usually feel during real quakes.
So in terms of ground movements people might feel, the rock avalanches “felt like 2.5,” Pankow says. “If this was a normal tectonic earthquake of magnitude 5, all three magnitude scales would give us similar answers.”
The slides were detected throughout the Utah seismic network, including its most distant station some 250 miles south on the Utah-Arizona border, Pankow says.
The Landslide Triggered 16 Tremors
The second rock avalanche was followed immediately by a real earthquake measuring 2.5 in Richter magnitude and 3.0 in coda magnitude, then three smaller quakes – all less than one-half mile below the bottom of the mine pit.
The Utah researchers sped up recorded seismic data by 30 times to create an audio file in which the second part of the slide is heard as a deep rumbling, followed by sharp gunshot-like bangs from three of the subsequent quakes.
Later analysis revealed another 12 tiny quakes – measuring from 0.5 to minus 0.8 Richter magnitude. (A minus 1 magnitude has one-tenth the power of a hand grenade.) Six of these tiny tremors occurred between the two parts of the landslide, five happened during the two days after the slide, and one was detected 10 days later, on April 20. No quakes were detected during the 10 days before the double landslide.
“We don’t know of any case until now where landslides have been shown to trigger earthquakes,” Moore says. “It’s quite commonly the reverse.”
A Long, Fast Landslide Runout
The landslide, from top to bottom, fell 2,790 vertical feet, but its runout – the distance the slide traveled – was almost 10,072 feet, or just less than two miles.
“It was a bedrock landslide that had a characteristically fast and long runout – much longer than we would see for smaller rockfalls and rockslides,” Moore says.
While no one was present to measure the speed, rock avalanches typically move about 70 mph to 110 mph, while the fastest moved a quickly as 220 mph.
So at Bingham Canyon, “we can safely say the material was probably traveling at least 100 mph as it fell down the steepest part of the slope,” Moore says.
The researchers don’t know why the slide happened as two rock avalanches instead of one, but Moore says, “A huge volume like this can fail in one episode or in 10 episodes over hours.”
The Seismograph Stations also recorded infrasound waves from the landslide, which Pankow says are “sound waves traveling through the atmosphere that we don’t hear” because their frequencies are so low.
Both seismic and infrasound recordings detected differences between the landslide’s two rock avalanches. For example, the first avalanche had stronger peak energy at the end that was lacking in the second slide, Pankow says.
“We’d like to be able to use data like this to understand the physics of these large landslides,” Moore says.
The seismic and infrasound recordings suggest the two rock avalanches were similar in volume, but photos indicate the first slide contained more bedrock, while the second slide contained a higher proportion of mined waste rock – although both avalanches were predominantly bedrock.
Note : The above story is based on materials provided by University of Utah
Chemical Formula: Pb21Cu20Cl42(OH)40 · 6H2O Locality: Boleo, near Santa Rosalia, Baja California Sur. Name Origin: Named for Edouard Cumenge (1828-1902), French mining engineer for the Boleo mines.
Cumengite is a rare mineral It shares a close relationship with another rare halide, boleite. Boleite and cumengite both come from the same type locality at Boleo, Baja California, Mexico; both resulted from the oxidation of igneous copper ore bodies; both have similar chemistries, although cumengite lacks silver; both have an attractive indigo blue color and both have interesting crystal forms. But all that is not the reason for the close relationship. Cumengite and boleite have about as close a relationship as two minerals can have since cumengite actually grows on the cube faces of boleite crystals.
The 20-km diameter Laguna del Maule caldera in the Chilean Andes was created by at least three very large eruptions that occurred 1.5, 0.95 and 0.34 million years ago. In contrast, over the last 25,000 years the volcano has erupted 36 small lava domes, like the one in the right foreground, the most recent of which formed 2,000 years ago. Understanding why volcanoes such as Laguna del Maule alternate between infrequent very large (or “super”) eruptions and frequent small eruptions is the subject of a recent paper in Nature Geoscience by Jon Blundy and Catherine Annen from the School of Earth Sciences and colleagues in Switzerland and France. Credit: University of Bristol
Factors determining the frequency and magnitude of volcanic phenomena have been uncovered by an international team of researchers.
Experts from the Universities of Geneva, Bristol and Savoie carried out over 1.2 million simulations to establish the conditions in which volcanic eruptions of different sizes occur.
The team used numerical modelling and statistical techniques to identify the circumstances that control the frequency of volcanic activity and the amount of magma that will be released.
The researchers, including Professor Jon Blundy and Dr Catherine Annen from Bristol University’s School of Earth Sciences, showed how different size eruptions have different causes. Small, frequent eruptions are known to be triggered by a process called magma replenishment, which stresses the walls around a magma chamber to breaking point. However, the new research shows that larger, less frequent eruptions are caused by a different phenomenon known as magma buoyancy, driven by slow accumulation of low-density magma beneath a volcano.
Predictions of the scale of the largest possible volcanic eruption on earth have been made using this new insight. This is the first time scientists have been able to establish a physical link between the frequency and magnitude of volcanic eruptions and their findings will be published today in the journal Nature Geoscience.
“We estimate that a magma chamber can contain a maximum of 35,000 km3 of eruptible magma. Of this, around 10 per cent is released during a super-eruption, which means that the largest eruption could release approximately 3,500 km3 of magma”, explained lead researcher Luca Caricchi, assistant professor at the Section of Earth and Environmental Sciences at the University of Geneva and ex-research fellow at the University of Bristol.
Volcanic eruptions may be frequent yet their size is notoriously hard to predict. For example, the Stromboli volcano in Italy ejects magma every ten minutes and would take two days to fill an Olympic swimming pool. However, the last super-eruption of a volcano, which occurred over 70,000 years ago, spewed out enough magma to fill a billion swimming pools.
This new research identifies the main physical factors involved in determining the frequency and size of eruptions and is essential to understanding phenomena that effect human life, such as the 2010 ash cloud caused by the eruption of Eyjafallajökull in Iceland.
Professor Jon Blundy said: “Some volcanoes ooze modest quantities of magma at regular intervals, whereas others blow their tops in infrequent super-eruptions. Understanding what controls these different types of behaviour is a fundamental geological question.
“Our work shows that this behaviour results from interplay between the rate at which magma is supplied to the shallow crust underneath a volcano and the strength of the crust itself. Very large eruptions require just the right (or wrong!) combination of magma supply and crustal strength.”
The above story is based on materials provided by University of Bristol
Indonesians look at the volcanic ash spewing up into the air from Mount Sinabung as it erupts in Karo, North Sumatra, on January 1, 2014
An Indonesian volcano that has erupted relentlessly for months shot volcanic ash into the air 30 times on Saturday, forcing further evacuations with more than 20,000 people now displaced, an official said.
Mount Sinabung on the western island of Sumatra sent rivers of lava flowing through an evacuation zone and columns of volcanic cloud up as high as 4,000 metres (13,000 feet), National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said.
“Hot lava spewed from the volcano some 60 times, reaching up to five kilometres (three miles) southeast of the crater. This outpour is the biggest we’ve seen in all the recent eruptions,” Nugroho said.
Authorities had already told residents in a five-kilometre radius of the volcano to evacuate, and Nugroho said an expanded evacuation zone may be considered.
The number of people who have now fled the rumbling volcano since it began erupting in September last year has risen to 20,331, Nugroho said.
Mount Sinabung is one of dozens of active volcanoes in Indonesia that straddle major tectonic fault lines, known as the Ring of Fire.
It had been quiet for around 400 years until it rumbled back to life in 2010, and again in September last year.
In August, five people were killed and hundreds evacuated when a volcano on a tiny island in East Nusa Tenggara province erupted.
The country’s most active volcano, Mount Merapi in central Java, killed more than 350 people in a series of violent eruptions in 2010.
Chemical Formula: CuFe2S3 Locality: Barracanao, Cuba. Name Origin: Named after its locality.
Cubanite is a yellow mineral of copper, iron, and sulfur, CuFe2S3.Cubanite was first described in 1843 for an occurrence in the Mayarí-Baracoa Belt, Oriente Province, Cuba.Cubanite occurs in high temperature hydrothermal deposits with pyrrhotite and pentlandite as intergrowths with chalcopyrite. It results from exsolution from chalcopyrite at temperatures below 200 to 210 °C. It has also been reported from carbonaceous chondrite meteorites.
Ancient flower. (Credit: Image courtesy of Oregon State University)
A 100-million-year old piece of amber has been discovered which reveals the oldest evidence of sexual reproduction in a flowering plant — a cluster of 18 tiny flowers from the Cretaceous Period — with one of them in the process of making some new seeds for the next generation.
The perfectly-preserved scene, in a plant now extinct, is part of a portrait created in the mid-Cretaceous when flowering plants were changing the face of the Earth forever, adding beauty, biodiversity and food. It appears identical to the reproduction process that “angiosperms,” or flowering plants still use today.
Researchers from Oregon State University and Germany published their findings on the fossils in the Journal of the Botanical Institute of Texas.
The flowers themselves are in remarkable condition, as are many such plants and insects preserved for all time in amber. The flowing tree sap covered the specimens and then began the long process of turning into a fossilized, semi-precious gem. The flower cluster is one of the most complete ever found in amber and appeared at a time when many of the flowering plants were still quite small.
Even more remarkable is the microscopic image of pollen tubes growing out of two grains of pollen and penetrating the flower’s stigma, the receptive part of the female reproductive system. This sets the stage for fertilization of the egg and would begin the process of seed formation — had the reproductive act been completed.
“In Cretaceous flowers we’ve never before seen a fossil that shows the pollen tube actually entering the stigma,” said George Poinar, Jr., a professor emeritus in the Department of Integrative Biology at the OSU College of Science. “This is the beauty of amber fossils. They are preserved so rapidly after entering the resin that structures such as pollen grains and tubes can be detected with a microscope.”
The pollen of these flowers appeared to be sticky, Poinar said, suggesting it was carried by a pollinating insect, and adding further insights into the biodiversity and biology of life in this distant era. At that time much of the plant life was composed of conifers, ferns, mosses, and cycads. During the Cretaceous, new lineages of mammals and birds were beginning to appear, along with the flowering plants. But dinosaurs still dominated the Earth.
“The evolution of flowering plants caused an enormous change in the biodiversity of life on Earth, especially in the tropics and subtropics,” Poinar said.
“New associations between these small flowering plants and various types of insects and other animal life resulted in the successful distribution and evolution of these plants through most of the world today,” he said. “It’s interesting that the mechanisms for reproduction that are still with us today had already been established some 100 million years ago.”
The fossils were discovered from amber mines in the Hukawng Valley of Myanmar, previously known as Burma. The newly-described genus and species of flower was named Micropetasos burmensis.
The above story is based on materials provided by Oregon State University.
Earthquake lights from Tagish Lake, Yukon-Alaska border region, around the 1st of July, probably 1972 or 1973 (exact date unknown). Estimated size: 1m diameter. Closest orbs slowly drifted up the mountain to join the more distant ones. Credit: Jim Conacher
Rare earthquake lights are more likely to occur on or near rift environments, where subvertical faults allow stress-induced electrical currents to flow rapidly to the surface, according to a new study published in the Jan./Feb. issue of Seismological Research Letters.From the early days of seismology, the luminous phenomena associated with some earthquakes have intrigued scholars. Earthquake lights (EQL) appear before or during earthquakes, but rarely after.
EQL take a variety of forms, including spheres of light floating through the air. Seconds before the 2009 L’Aquila, Italy earthquake struck, pedestrians saw 10-centimeter high flames of light flickering above the stone-paved Francesco Crispi Avenue in the town’s historical city center. On Nov. 12, 1988, a bright purple-pink globe of light moved through the sky along the St. Lawrence River near the city of Quebec, 11 days before a powerful quake. And in 1906, about 100 km northwest of San Francisco, a couple saw streams of light running along the ground two nights preceding that region’s great earthquake.
Continental rift environments now appear to be the common factor associated with EQL. In a detailed study of 65 documented EQL cases since 1600 A.D., 85 percent appeared spatially on or near rifts, and 97 percent appeared adjacent to subvertical faults (a rift, a graben, strike-slip or transform fault). Intraplate faults are associated with just 5 percent of Earth’s seismic activity, but 97 percent of documented cases of earthquake lights.
“The numbers are striking and unexpected,” said Robert Thériault, a geologist with the Ministère des Ressources Naturelles of Québec, who, along with colleagues, culled centuries of literature references, limiting the cases in this study to 65 of the best-documented events in the Americas and Europe.
“We don’t know quite yet why more earthquake light events are related to rift environments than other types of faults,” said Thériault, “but unlike other faults that may dip at a 30-35 degree angle, such as in subduction zones, subvertical faults characterize the rift environments in these cases.”
Two of the 65 EQL events are associated with subduction zones, but Thériault suggests there may be an unknown subvertical fault present. “We may not know the fault distribution beneath the ground,” said Thériault. “We have some idea of surface structures, but sedimentary layers or water may obscure the underlying fault structure.”
While the 65 earthquakes ranged in magnitude, from M 3.6 to 9.2, 80 percent were greater than M 5.0. The EQL varied in shape and extent, though most commonly appeared as globular luminous masses, either stationary or moving, as atmospheric illuminations or as flame-like luminosities issuing from the ground.
Timing and distance to the epicenter vary widely. Most EQL are seen before and/or during an earthquake, but rarely after, suggesting to the authors that the processes responsible for EQL formation are related to a rapid build-up of stress prior to fault rupture and rapid local stress changes during the propagation of the seismic waves. Stress-activated mobile electronic charge carriers, termed positive holes, flow swiftly along stress gradients. Upon reaching the surface, they ionize air molecules and generate the observed luminosities.
Eyewitness reports and security cameras captured a large number of light flashes during the 2007 Pisco, Peru M 8.0 earthquake. Together with seismic records obtained on a local university campus, the automatic security camera records allow for an exact timing and location of light flashes that illuminated a large portion of the night sky. The light flashes identified as EQL coincided with the passage of the seismic waves.
Thériault likes the account of a local L’Aquila resident, who, after seeing flashes of light from inside his home two hours before the main shock, rushed his family outside to safety.
“It’s one of the very few documented accounts of someone acting on the presence of earthquake lights,” said Thériault. “Earthquake lights as a pre-earthquake phenomenon, in combination with other types of parameters that vary prior to seismic activity, may one day help forecast the approach of a major quake,” said Thériault.
Note : The above story is based on materials provided by Seismological Society of America
“The high radiogenic heat generation in the Darling Range appears to be the cause of the hot water within the Perth Basin, as the granites of the Darling Range extend under the Perth Basin, which provides the sedimentary blanket,” Dr Middleton says. Credit: Michael Jefferies
Scientists investigating heat decay from radiogenic granite in the Darling Range have discovered the maximum heat output has exceeded previously known data.
Radiogenic granite, the major rock form of the Darling Range, is known for naturally high elemental concentrations of uranium (U), thorium (Th) and potassium (K).
During radioactive decay the elements release heat, and it is at depths of 3000–4000 metres that temperatures can attain 60 to 110C, making them viable for thermal applications.
Department of Mines and Petroleum research scientist Dr Mike Middleton says the thermal effect can also be observed at the base of a sedimentary rock layer, as is the case for the Perth Basin that lies over the Yilgarn Craton.
The Darling Range is at the boundary of both the Perth Basin and the Yilgarn Craton.
“In addition to establishing the amount of radiogenic heat generation in the Darling Range granites, the study was also about understanding the temperatures that might exist at depth in the Darling Range and adjacent Perth Basin,” he says.
Measuring exposed granite at 13 sites across the Darling Range using a Geiger Muller counter and RS 125 Spectrometer Dr Middleton and his team were able to model the data as an estimation of heat production.
Results indicate providing a uniform thickness in the granite profile (of 6km), heat generation can be within the vicinity of 50C at 1000m, 75C at 2000m, 100C at 3000m and 120C at 4000m.
Despite these geothermally considered lower temperatures Dr Middleton says this, “has a significant role to play in Perth’s energy mix, albeit with low-temperature applications”.
“The high radiogenic heat generation in the Darling Range appears to be the cause of the hot water within the Perth Basin, as the granites of the Darling Range extend under the Perth Basin, which provides the sedimentary blanket.”
“Indeed, hot water springs were noted in Dalkeith, near the Swan River, back in the early 1900s.”
Metropolitan Perth is ideally situated to take advantage of the low temperature geothermal energy, especially by the use of organic Rankine-cycle turbines or absorption chillers that operate at 70–120C.
“A current study is being carried out in the Vasse region, where hot pools and natural hot springs may be developed to support the tourist industry, especially in the colder months of the year,” he says.
Geothermal potential may also occur in Albany and Esperance.
Dr Middleton says studies are continuing in the regions south of Perth.
Note : The above story is based on materials provided by Science Network WA
This is a profile depicting the height and depth of the Atlas Mountains. The blue bars indicate the boundary between the crust and the superhot rock below, about 15 km shallower than predicted by previous models. Credit: Meghan Miller and Thorsten Becker
The Atlas Mountains defy the standard model for mountain structure in which high topography must have deep roots for support, according to a new study from Earth scientists at USC.
In a new model, the researchers show that the mountains are floating on a layer of hot molten rock that flows beneath the region’s lithosphere, perhaps all the way from the volcanic Canary Islands, just offshore northwestern Africa.
“Our findings confirm that mountain structures and their formation are far more complex than previously believed,” said lead author Meghan Miller, assistant professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences.
The study, coauthored by Thorsten Becker, professor of Earth sciences at USC Dornsife, was published by Geology on Jan. 1, 2014 and highlighted by Nature Geoscience.
A well-established model for the Earth’s lithosphere suggests that the height of the Earth’s crust must be supported by a commensurate depth, much like how a tall iceberg doesn’t simply float on the surface of the water but instead rests on a large submerged mass of ice. This property is known as “istostacy.”
“The Atlas Mountains are at present out of balance, likely due to a confluence of existing lithospheric strength anomalies and deep mantle dynamics,” Becker said.
Miller and Becker used seismometers to measure the thickness of the lithosphere – that is, the Earth’s rigid outermost layer – beneath the Altas Mountains in Morocco. By analyzing 67 distant seismic events with 15 seismometers, the team was able to use the Earth’s vibrations to “see” into the deep subsurface.
They found that the crust beneath the Atlas Mountains, which rise to an elevation of more than 4,000 meters, reaches a depth of only about 35 km – about 15 km shy of what the traditional model predicts.
“This study shows that deformation can be observed through the entire lithosphere and contributes to mountain building even far away from plate boundaries” Miller said.
Miller’s lab is currently conducting further research into the timing and effects of the mountain building on other geological processes.
Note : The above story is based on materials provided by University of Southern California
Chemical Formula: Fe22+Fe3+((Si,Fe3+)2O5)(OH)4 Locality: Pribram and Kuttenberg, Bohemia of Czechoslovakia. Name Origin: Named for Axel Fredrik Cronstedt (1722-1765), Swedish mineralogist and chemist.
Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. It has a formula of Fe22+Fe3+((Si,Fe3+)2O5)(OH)4.
It was discovered in 1821 and named in honor of Swedish mineralogist Axel Fredrik Cronstedt (1722–1765). It has been found in Bohemia in the Czech Republic and in Cornwall, England.
Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.
Computer simulation of the processes in the Earth’s mantle Credit: Institute of Geosciences, JGU
Earth’s mantle temperatures during the Archean eon, which commenced some 4 billion years ago, were significantly higher than they are today. According to recent model calculations, the Archean crust that formed under these conditions was so dense that large portions of it were recycled back into the mantle.
This is the conclusion reached by Dr. Tim Johnson who is currently studying the evolution of the Earth’s crust as a member of the research team led by Professor Richard White of the Institute of Geosciences at Johannes Gutenberg University Mainz (JGU). According to the calculations, this dense primary crust would have descended vertically in drip form. In contrast, the movements of today’s tectonic plates involve largely lateral movements with oceanic lithosphere recycled in subduction zones. The findings add to our understanding of how cratons and plate tectonics, and thus also the Earth’s current continents, came into being.
Because mantle temperatures were higher during the Archean eon, the Earth’s primary crust that formed at the time must have been very thick and also very rich in magnesium. However, as Johnson and his co-authors explain in their article recently published in Nature Geoscience, very little of this original crust is preserved, indicating that most must have been recycled into the Earth’s mantle. Moreover, the Archean crust that has survived in some areas such as, for example, Northwest Scotland and Greenland, is largely made of tonalite–trondhjemite–granodiorite complexes and these are likely to have originated from a hydrated, low-magnesium basalt source. The conclusion is that these pieces of crust cannot be the direct products of an originally magnesium-rich primary crust. These TTG complexes are among the oldest features of our Earth’s crust. They are most commonly present in cratons, the oldest and most stable cores of the current continents.
With the help of thermodynamic calculations, Dr. Tim Johnson and his collaborators at the US-American universities of Maryland, Southern California, and Yale have established that the mineral assemblages that formed at the base of a 45-kilometer-thick magnesium-rich crust were denser than the underlying mantle layer. In order to better explore the physics of this process, Professor Boris Kaus of the Geophysics work group at Mainz University developed new computer models that simulate the conditions when the Earth was still relatively young and take into account Johnson’s calculations.
These geodynamic computer models show that the base of a magmatically over-thickened and magnesium-rich crust would have been gravitationally unstable at mantle temperatures greater than 1,500 to 1,550 degrees Celsius and this would have caused it to sink in a process called ‘delamination’. The dense crust would have dripped down into the mantle, triggering a return flow of mantle material from the asthenosphere that would have melted to form new primary crust. Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to provide a source of the tonalite–trondhjemite–granodiorite complexes. The dense residues of these processes, which would have a high content of mafic minerals, must now reside in the mantle.
Note : The above story is based on materials provided by Universitaet Mainz
Chemical Formula: Pb(CrO4) Locality: Tasmania. Name Origin: From the Greek krokos, meaning “crocus” or “saffron.”
Crocoite is a mineral consisting of lead chromate, Pb(CrO4), and crystallizing in the monoclinic crystal system. It is identical in composition with the artificial product chrome yellow used as a paint pigment.
Crocoite is commonly found as large, well-developed prismatic crystals, although in many cases are poorly terminated. Crystals are of a bright hyacinth-red color, translucent, and have an adamantine to vitreous lustre. On exposure to UV light some of the translucency and brilliancy is lost.
The streak is orange-yellow; Mohs hardness is 2.5–3; and the specific gravity is 6.0.It was discovered at the Berezovskoe Au Deposit (Berezovsk Mines) near Ekaterinburg in the Urals in 1766; and named crocoise by F. S. Beudant in 1832, from the Greek κρόκος (krokos), saffron, in allusion to its color, a name first altered to crocoisite and afterwards to crocoite. In the type locality the crystals are found in gold-bearing quartz-veins traversing granite or gneiss and associated with crocoite are quartz, embreyite, phoenicochroite and vauquelinite.
Phoenicochroite is a basic lead chromate, Pb2CrO5 with dark red crystals, and vauquelinite a lead and copper phosphate-chromate, Pb2CuCrO4PO4OH, with brown or green monoclinic crystals. Vauquelinite was named after L. N. Vauquelin, who in 1797 discovered (simultaneously with and independently of M. H. Klaproth) the element chromium in crocoite.
Abundant masses with exceptional examples of crocoite crystals have been found in the Extended Mine at Mount Dundas as well as the Adelaide, Red Lead, West Comet, Platt and a few other Mines at Dundas, Tasmania; they are usually found in long slender prisms, usually about 10–20 mm but rarely up to 200 mm (4 inches) in length, with a brilliant lustre and color. Crocoite is also the official Tasmanian mineral emblem. Other localities which have yielded good crystallized specimens are Congonhas do Campo near Ouro Preto in Brazil, Luzon in the Philippines, Mutare in Mashonaland, near Menzies in Western Australia, plus Brazil, Germany and South Africa.
The relative rarity of crocoite is connected with the specific conditions required for its formation: an oxidation zone of lead ore bed and presence of ultramafic rocks serving as the source of chromium (in chromite). Oxidation of Cr3+ into CrO42− (from chromite) and decomposition of galena (or other primary lead minerals) are required for crocoite formation. These conditions are relatively unusual.
As crocoite is composed of lead(II) chromate, it is toxic, containing both lead and hexavalent chromium.
The Phanerozoic is the current geologic eon in the geologic time scale, and the one during which abundant animal life has existed. It covers roughly 542 million years (541.0 ± 1.0) and goes back to the time when diverse hard-shelled animals first appeared. Its name derives from the Ancient Greek words φανερός and ζωή, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon. The time before the Phanerozoic, called the Precambrian supereon, is now divided into the Hadean, Archaean and Proterozoic eons.
The time span of the Phanerozoic includes the rapid emergence of a number of animal phyla; the evolution of these phyla into diverse forms; the emergence and development of complex plants; the evolution of fish; the emergence of insects and tetrapods; and the development of modern faunas. During this time span tectonic forces caused the continents to move and eventually collect into a single landmass known as Pangaea, which then separated into the current continental landmasses
The Proterozoic-Phanerozoic boundary happened 541.0 ± 1.0 million years ago. In the 19th Century, the boundary was set at the first abundant animal (metazoan) fossils. But several hundred groups (taxa) of metazoa of the earlier Proterozoic era have been identified since systematic study of those forms started in the 1950s. Most geologists and paleontologists would probably set the Proterozoic-Phanerozoic boundary either at the classic point where the first trilobites and reef building animals (archaeocyatha) such as corals and others appear; at the first appearance of a complex feeding burrow called Treptichnus pedum; or at the first appearance of a group of small, generally disarticulated, armored forms termed ‘the small shelly fauna’. The three different dividing points are within a few million years of each other.
The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. In the older literature, the term Phanerozoic is generally used as a label for the time period of interest to paleontologists, but that use of the term seems to be falling into disuse in more modern literature.
Biodiversity
It has been demonstrated that changes in biodiversity through the Phanerozoic correlate much better with the
During, the Phanerozoic biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera
hyperbolic model (widely used in demography and macrosociology) than with exponential and logistic models (traditionally used in population biology and extensively applied to fossil biodiversity as well). The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) and/or a negative feedback arising from resource limitation. The hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the world population growth arises from a second-order positive feedback between the population size and the rate of technological growth.[1] The character of biodiversity growth in the Phanerozoic can be similarly accounted for by a feedback between the diversity and community structure complexity. It is suggested that the similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the interference of the hyperbolic trend with cyclical and stochastic dynamics.
Note : The above story is based on materials provided by Wikipedia
Green Tuff ignimbrite draping the outer caldera wall at Salto La Vecchia.
For the first time scientists have tracked how one of the deadliest volcanic hazards moves over time.Pyroclastic density currents are searing hot clouds of ash and gas released by volcanoes; they travel up to 450 miles per hour. Their speed and intense heat make it nearly impossible for humans to observe – anybody who got close enough to monitor one would be killed.
But scientists from the University of Leicester have developed a novel way of reconstructing how one of these currents flowed. Their technique showed for the first time that instead of flowing radially out from the volcano and covering everything in their path, these currents move initially in one direction, but that this direction then changes.
‘In the magma chamber under a volcano the chemistry of the magma at the top is different to the chemistry at the bottom. During an eruption these chemical zones are erupted at different times, so if something was erupted at the beginning it would show a record matching the chemical zone from the top of the magma chamber,’ explains Dr Rebecca Williams, now of the University of Hull, lead author on the project. ‘We realised that if I could find a chemical zoning in an ignimbrite I could use it as a proxy for time.’
The research, published in the journal Geology, looked at a deposit on the volcanic island of Panetelleria left by one of these pyroclastic density currents during an eruption 45,000 years ago.
‘The Green Tuff on Panetelleria was huge. It was much bigger than the ones that buried Pompeii and Herculaneum,’ says Williams. ‘It was very hot when it was deposited which means it welded and turned into a green volcanic glass that covers the entire island. It hasn’t really been weathered, which means it is incredibly well preserved. It is an incredible exposure.’
A close up of that caldera wall showing the Green Tuff draping over the older ignimbrites.
The chemical structure of this deposit, called the Green Tuff ignimbrite, varies from the bottom to the top, in a similar way to the variation in a magma chamber.
‘If you just look at a deposit you can’t tell it’s zoned. You can’t see it with the naked eye, although sometimes there may be an increase in the size or amount of some crystals. So I took closely spaced samples vertically through the deposit and did a chemical analysis of them to get the chemical compostion from it.’ Williams says.
The team matched the variation seen in the Green Tuff with the same layers in the magma chamber to assess at what point during the eruption they flowed.
They were surprised to discover that the circular deposits often left by these currents didn’t mean that they flowed out in a circle out from the eruption.
‘These really big currents tend to have circular deposit shapes to them so people often think deposits expand radially, going out in all directions at the same time. We’re actually able to show that didn’t happen, it’s only at the climatic phase of an eruption that it flows in all directions at the same time,’ Williams explains.
‘With the Green Tuff the current gradually went over the landscape, it was going off in one direction first and as it moved it was initially blocked by lots of topography, but as it continued moving it would start to creep around and eventually go over any barriers,’ she continues.
The team also showed for the first time that as the eruption tapered off, the pyroclastic density current couldn’t flow as far, so the leading edge appears to retreat over time.
‘This gives us a much better understanding of how pyroclastic density currents behave so it will be a huge help with hazard mapping. It’s really good to know that we can’t think of these phenomena as one very rapid event,’ concludes Williams.
Note : The above story is based on materials provided by PlanetEarth Online
In this Monday, Dec. 2, 2013 photo, a guide stands at the entrance of a cave which scientists said reveals history of ancient tsunamis in Lhong, Aceh province, Indonesia. The cave discovered near the source of 2004’s massive earthquake-spawned tsunami in Indonesia contains the footprints of past gigantic waves dating up to 7,500 years ago, a rare natural record suggesting future generations living in the coastal area must stay prepared because disasters can occur in relatively short bursts or after long lulls. (AP Photo/Heri Juanda)
A cave discovered near the source of Indonesia’s massive earthquake-spawned tsunami contains the footprints of past gigantic waves dating up to 7,500 years ago, a rare natural record that suggests the next disaster could be centuries away—or perhaps only decades.
The findings provide the longest and most detailed timeline for tsunamis that have occurred off the far western tip of Sumatra island in Aceh province. That’s where 100-foot (30-meter) waves triggered by a magnitude-9.1 earthquake on Dec. 26, 2004, killed 230,000 people in several countries, more than half of them in Indonesia.
The limestone cave, located within a couple hundred yards (meters) of the coast near Banda Aceh, is about 3 feet (1 meter) above knee-high tide and protected from storms and wind. Only huge waves that inundate the coastal area are able to gush inside.
Researchers in 2011 uncovered seabed sand deposits that were swept into the cave over thousands of years and neatly layered between bat droppings like a geological cake. Radiocarbon analysis of materials, including clamshells and the remains of microscopic organisms, provided evidence of 11 tsunamis before 2004.
The disasters were by no means evenly spaced, said lead researcher Charles Rubin from the Earth Observatory of Singapore. The last one occurred about 2,800 years ago, but there were four others in the preceding 500 years.
And it’s possible there were others. Researchers know, for instance, that there were two mammoth earthquakes in the region around 1393 and 1450. Rubin said a big tsunami could have carried away evidence of other events through erosion.
The scientists are still working to determine the size of the waves that entered the cave.
“The take-home message is perhaps that the 2004 event doesn’t mean it won’t happen for another 500 years,” said Rubin, who added that the cave was discovered by chance and not part of planned field work. “We did see them clustered together closer in time. I wouldn’t put out a warning that we’re going to have an earthquake, but it shows that the timing is really variable.”
The quake that triggered the 2004 tsunami surprised scientists because the fault that unleashed the megathrust temblor had been quiet for hundreds of years. And since the last big earthquake had struck more than 500 years earlier, there was no surviving oral history that could have helped people understand the risk.
Since 2004, much research has been done to try to learn about the area’s past by examining sand deposits, uplifted coral and GPS data.
“The findings are very significant,” Katrin Monecke, a geosciences professor at Wellesley College in Massachusetts wrote in an email. She worked on tsunami sand deposits discovered in marshes in the area, but was not involved with the cave research, which was presented this month at an American Geophysical Union conference in San Francisco. “The sand sheets in the cave cover a very long time span and give an excellent idea about earthquake frequency.”
Despite the long record preserved in the cave, Rubin said it did not provide any clear clues about tsunami frequency or when events might happen in a relatively close period of time.
Geologist Kerry Sieh, director of the Singapore group and also part of the cave investigation, has predicted that another monster quake could rock the area in the next few decades. They tend to come in cycles and the 2004 temblor heaped more pressure on the fault. However, the history is so variable, it’s impossible to make an exact forecast.
“By learning about the type of tsunamis that happened in the past, maybe we can do planning for mitigation for the next tsunami,” said Nazli Ismail, head of the physics and geophysics department at Syiah Kuala University in Banda Aceh who worked on the project.
Indonesia is an archipelago located on the so-called “Ring of Fire,” a horseshoe of fault lines and volcanoes surrounding the Pacific Basin. It is home to some of the world’s biggest and deadliest seismic activity.
Note : The above story is based on materials provided by The Associated Press. All rights reserved.
Riebeckite forms in two very different habits. The darker-colored forms which are individually crystallized are generally of igneous origin, such as volcanic rock and pegmatites. The finely fibrous variety, known as Crocidolite, usually originates from altered metamorphic rocks. The Crocidolite variety is a type of asbestos, and is sometimes also referred to as “blue asbestos”.
It is considered to be the most hazardous form of asbestos, and should never be brought near the mouth. If its fibers or particles enter the lungs, they can cause asbestosis. Asbestosis is a lung disease caused by inhalation of asbestos particles, which causes several cancers, particularly lung cancer and mesothelioma. Symptoms of asbestosis do not arise until about 20 years after the inhalation. Due to the hazards, washing hands after handling specimens is highly recommended. Many mineral collectors avoid collecting asbestos minerals out of safety concerns.
Chemical Formula: [Na2][Z32+Fe23+]Si8O22(OH,F,Cl)2 Locality: Socotra island, Indian Ocean, Yemen. Name Origin: Named after the German traveler, Emil Riebeck (1853-1885).
Local seismometers detect clusters of intermediate-depth earthquakes in and around the Colombian city of Bucaramanga. The epicenter of the quakes, more than 50 kilometers below the surface, is known as the “Nest.” Credit: MIT
Nearly 25 percent of earthquakes occur more than 50 kilometers below the Earth’s surface, when one tectonic plate slides below another, in a region called the lithosphere. Scientists have thought that these rumblings from the deep arise from a different process than shallower, more destructive quakes. But limited seismic data, and difficulty in reproducing these quakes in the laboratory, have combined to prevent researchers from pinpointing the cause of intermediate and deep earthquakes.
Now a team from MIT and Stanford University has identified a mechanism that helps these deeper quakes spread. By analyzing seismic data from a region in Colombia with a high concentration of intermediate-depth earthquakes, the researchers identified a “runaway process” in which the sliding of rocks at great depths causes surrounding temperatures to spike. This influx of heat, in turn, encourages more sliding—a feedback mechanism that propagates through the lithosphere, generating an earthquake.
German Prieto, an assistant professor of geophysics in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says that once thermal runaway starts, the surrounding rocks can heat up and slide more easily, raising the temperature very quickly.
“What we predict is for medium-sized earthquakes, with magnitude 4 to 5, temperature can rise up to 1,000 degrees Centigrade, or about 1,800 degrees Fahrenheit, in a matter of one second,” Prieto says. “It’s a huge amount. You’re basically allowing rupture to run away because of this large temperature increase.”
Prieto says that understanding deeper earthquakes may help local communities anticipate how much shaking they may experience, given the seismic history of their regions.
He and his colleagues have published their results in the journal Geophysical Research Letters.
The majority of Earth’s seismic activity occurs at relatively shallow depths, and the mechanics of such quakes is well understood: Over time, abutting plates in the crust build up tension as they shift against each other. This tension ultimately reaches a breaking point, creating a sudden rupture that splinters through the crust.
However, scientists have determined that this process is not feasible for quakes that occur far below the surface. Essentially, higher temperatures and pressures at these depths would make rocks behave differently than they would closer to the surface, gliding past rather than breaking against each other.
By way of explanation, Prieto draws an analogy to glass: If you try to bend a glass tube at room temperature, with enough force, it will eventually shatter. But with heating, the tube will become much more malleable, and bend without breaking.
So how do deeper earthquakes occur? Scientists have proposed two theories: The first, called dehydration embrittlement, is based on the small amounts of water in rocks’ mineral composition. At high pressure and heat, rocks release water, which lubricates surrounding faults, creating fractures that ultimately set off a quake.
The second theory is thermal runaway: Increasing temperatures weaken rocks, promoting slippage that spreads through the lithosphere, further increasing temperatures and causing more rocks to slip, resulting in an earthquake.
Probing the nest
Prieto and his colleagues found new evidence in support of the second theory by analyzing seismic data from a region of Colombia that experiences large numbers of intermediate-depth earthquakes—quakes whose epicenters are 50 to 300 kilometers below the surface. This region, known as the Bucaramanga Nest, hosts the highest concentration of intermediate-depth quakes in the world: Since 1993, more than 80,000 earthquakes have been recorded in the area, making it, in Prieto’s view, an “ideal natural laboratory” for studying deeper quakes.
The researchers analyzed seismic waves recorded by nearby surface seismometers and calculated two parameters: stress drop, or the total amount of energy released by an earthquake, and radiated seismic energy, or the amount of that energy that makes it to the surface as seismic waves—energy that is manifested in the shaking of the ground.
The stronger a quake is, the more energy, or heat, it generates. Interestingly, the MIT group found that only 2 percent of a deeper quake’s total energy is felt at the surface. Prieto reasoned that much of the other 98 percent may be released locally as heat, creating an enormous temperature increase that pushes a quake to spread.
Prieto says the study provides strong evidence for thermal runaway as the likely mechanism for intermediate-depth earthquakes. Such knowledge, he says, may be useful for communities around Bucaramanga in predicting the severity of future quakes.
“Usually people in Bucaramanga feel a magnitude 4 quake every month or so, and every year they experience a larger one that can shake significantly,” Prieto says. “If you’re in a region where you have intermediate-depth quakes and you know the size of the region, you can make a prediction of the type of magnitudes of quakes that you can have, and what kind of shaking you would expect.”
Prieto, a native Colombian, plans to deploy seismic stations above the Bucaramanga Nest to better understand the activity of deeper quakes.
Note : The above story is based on materials provided by Massachusetts Institute of Technology
Glaciologist Lora Koenig (left) operates a video recorder that has been lowered into the bore hole to observe the ice structure of the aquifer in April 2013. Credit: University of Utah/Clément Miège
Buried underneath compacted snow and ice in Greenland lies a large liquid water reservoir that has now been mapped by researchers using data from NASA’s Operation IceBridge airborne campaign.
A team of glaciologists serendipitously found the aquifer while drilling in southeast Greenland in 2011 to study snow accumulation. Two of their ice cores were dripping water when the scientists lifted them to the surface, despite air temperatures of minus 4 F (minus 20 C). The researchers later used NASA’s Operation Icebridge radar data to confine the limits of the water reservoir, which spreads over 27,000 square miles (69,930 square km) – an area larger than the state of West Virginia. The water in the aquifer has the potential to raise global sea level by 0.016 inches (0.4 mm).
“When I heard about the aquifer, I had almost the same reaction as when we discovered Lake Vostok [in Antarctica]: it blew my mind that something like that is possible,” said Michael Studinger, project scientist for Operation IceBridge, a NASA airborne campaign studying changes in ice at the poles. “It turned my view of the Greenland ice sheet upside down – I don’t think anyone had expected that this layer of liquid water could survive the cold winter temperatures without being refrozen.”
Southeast Greenland is a region of high snow accumulation. Researchers now believe that the thick snow cover insulates the aquifer from cold winter surface temperatures, allowing it to remain liquid throughout the year. The aquifer is fed by meltwater that percolates from the surface during the summer.
The new research is being presented in two papers: one led by University of Utah’s Rick Forster that was published on Dec. 22 in the journal Nature Geoscience and one led by NASA’s Lora Koenig that has been accepted for publication in the journal Geophysical Research Letters. The findings will significantly advance the understanding of how melt water flows through the ice sheet and contributes to sea level rise.
When a team led by Forster accidentally drilled into water in 2011, they weren’t able to continue studying the aquifer because their tools were not suited to work in an aquatic environment. Afterward, Forster’s team determined the extent of the aquifer by studying radar data from Operation IceBridge together with ground-based radar data. The top of the water layer clearly showed in the radar data as a return signal brighter than the ice layers.
Koenig, a glaciologist with NASA’s Goddard Space Flight Center in Greenbelt, Md., co-led another expedition to southeast Greenland with Forster in April 2013 specifically designed to study the physical characteristics of the newly discovered water reservoir. Koenig’s team extracted two cores of firn (aged snow) that were saturated with water. They used a water-resistant thermoelectric drill to study the density of the ice and lowered strings packed with temperature sensors down the holes, and found that the temperature of the aquifer hovers around 32 F (zero C), warmer than they had expected it to be.
Koenig and her team measured the top of the aquifer at around 39 feet (12 meters) under the surface. This was the depth at which the boreholes filled with water after extracting the ice cores. They then determined the amount of water in the water-saturated firn cores by comparing them to dry cores extracted nearby. The researchers determined the depth at which the pores in the firn close, trapping the water inside the bubbles – at this point, there is a change in the density of the ice that the scientists can measure. This depth is about 121 feet (37 meters) and corresponds to the bottom of the aquifer. Once Koenig’s team had the density, depth and spatial extent of the aquifer, they were able to come up with an estimated water volume of about 154 billion tons (140 metric gigatons). If this water was to suddenly discharge to the ocean, this would correspond to 0.016 inches (0.4 mm) of sea level rise.
Researchers think that the perennial aquifer is a heat reservoir for the ice sheet in two ways: melt water carries heat when it percolates from the surface down the ice to reach the aquifer. And if the trapped water were to refreeze, it would release latent heat. Altogether, this makes the ice in the vicinity of the aquifer warmer, and warmer ice flows faster toward the sea.
“Our next big task is to understand how this aquifer is filling and how it’s discharging,” said Koenig. “The aquifer could offset some sea level rise if it’s storing water for long periods of time. For example after the 2012 extreme surface melt across Greenland, it appears that the aquifer filled a little bit. The question now is how does that water leave the aquifer on its way to the ocean and whether it will leave this year or a hundred years from now.”
Note : The above story is based on materials provided by NASA’s Goddard Space Flight Center
