Tiny ‘spherules’ reveal details about Earth’s asteroid impacts

Researchers are learning details about asteroid impacts going back to the Earth's early history by using a new method for extracting precise information from tiny 'spherules' embedded in layers of rock. The spherules were created when asteroids crashed into Earth, vaporizing rock that expanded as a giant vapor plume. Small droplets of molten rock in the plume condensed and solidified, falling back to the surface as a thin layer. This sample was found in Western Australia and formed 2.63 billion years ago in the aftermath of a large impact. -  Oberlin College photo/Bruce M. Simonson
Researchers are learning details about asteroid impacts going back to the Earth’s early history by using a new method for extracting precise information from tiny ‘spherules’ embedded in layers of rock. The spherules were created when asteroids crashed into Earth, vaporizing rock that expanded as a giant vapor plume. Small droplets of molten rock in the plume condensed and solidified, falling back to the surface as a thin layer. This sample was found in Western Australia and formed 2.63 billion years ago in the aftermath of a large impact. – Oberlin College photo/Bruce M. Simonson

Researchers are learning details about asteroid impacts going back to the Earth’s early history by using a new method for extracting precise information from tiny “spherules” embedded in layers of rock.

The spherules were created when asteroids crashed into the Earth, vaporizing rock that expanded into space as a giant vapor plume. Small droplets of molten and vaporized rock in the plume condensed and solidified, falling back to Earth as a thin layer. The round or oblong particles were preserved in layers of rock, and now researchers have analyzed them to record precise information about asteroids impacting Earth from 3.5 billion to 35 million years ago.

“What we have done is provide the foundation for understanding how to interpret the layers in terms of the size and velocity of the asteroid that made them,” said Jay Melosh, an expert in impact cratering and a distinguished professor of earth and atmospheric sciences, physics and aerospace engineering at Purdue University.

Findings, which support a theory that the Earth endured an especially heavy period of asteroid bombardment early in its history, are detailed in a research paper appearing online in the journal Nature on Wednesday (April 25). The paper was written by Purdue physics graduate student Brandon Johnson and Melosh. The findings, based on geologic observations, support a theoretical study in a companion paper in Nature by researchers at the Southwest Research Institute in Boulder, Colo.

The period of heavy asteroid bombardment – from 4.2 to 3.5 billion years ago – is thought to have been influenced by changes in the early solar system that altered the trajectory of objects in an asteroid belt located between Mars and Jupiter, sending them on a collision course with Earth.

“That’s the postulate, and this is the first real solid evidence that it actually happened,” Melosh said. “Some of the asteroids that we infer were about 40 kilometers in diameter, much larger than the one that killed off the dinosaurs about 65 million years ago that was about 12-15 kilometers. But when we looked at the number of impactors as a function of size, we got a curve that showed a lot more small objects than large ones, a pattern that matches exactly the distribution of sizes in the asteroid belt. For the first time we have a direct connection between the crater size distribution on the ancient Earth and the sizes of asteroids out in space.”

Because craters are difficult to study directly, impact history must be inferred either by observations of asteroids that periodically pass near the Earth or by studying craters on the moon. Now, the new technique using spherules offers a far more accurate alternative to chronicle asteroid impacts on Earth, Melosh said.

“We can look at these spherules, see how thick the layer is, how big the spherules are, and we can infer the size and velocity of the asteroid,” Melosh said. “We can go back to the earliest era in the history of the Earth and infer the population of asteroids impacting the planet.”

For asteroids larger than about 10 kilometers in diameter, the spherules are deposited in a global layer.

“Some of these impacts were several times larger than the Chicxulub impact that killed off the dinosaurs 65 million years ago,” Johnson said. “The impacts may have played a large role in the evolutional history of life. The large number of impacts may have helped simple life by introducing organics and other important materials at a time when life on Earth was just taking hold.”

A 40-kilometer asteroid would have wiped out everything on the Earth’s surface, whereas the one that struck 65 million years ago killed only land animals weighing more than around 20 kilograms.

“Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes,” Johnson said. “However, the spherule layers, if preserved in the geologic record, provide information about an impact even when the source crater cannot be found.”

The Purdue researchers studied the spherules using computer models that harness mathematical equations developed originally to calculate the condensation of vapor.

“There have been some new wrinkles in vapor condensation modeling that motivated us to do this work, and we were the first to apply it to asteroid impacts,” Melosh said.

The spherules are about a millimeter in diameter.

The researchers also are studying a different type of artifact similar to spherules but found only near the original impact site. Whereas the globally distributed spherules come from the condensing vaporized rock, these “melt droplets” are from rock that’s been melted and not completely vaporized.

“Before this work, it was not possible to distinguish between these two types of formations,” Melosh said. “Nobody had established criteria for discriminating between them, and we’ve done that now.”

One of the authors of the Southwest Research Institute paper, David Minton, is now an assistant professor of earth and atmospheric sciences at Purdue.

Findings from the research may enable Melosh’s team to enhance an asteroid impact effects calculator he developed to estimate what would happen if asteroids of various sizes were to hit the Earth. The calculator, “Impact: Earth!” allows anyone to calculate potential comet or asteroid damage based on the object’s mass.

Fracking requires a minimum distance of at least 0.6 kilometers from sensitive rock strata

This is Professor Richard Davies. -  Durham University
This is Professor Richard Davies. – Durham University

The chances of rogue fractures due to shale gas fracking operations extending beyond 0.6 kilometers from the injection source is a fraction of one percent, according to new research led by Durham University.

The analysis is based on data from thousands of fracking operations in the USA and natural rock fractures in Europe and Africa.

It is believed to be the first analysis of its type and could be used across the world as a starting point for setting a minimum distance between the depth of fracking and shallower aquifers used for drinking water.

The new study, published in the journal Marine and Petroleum Geology, shows the probabilities of ‘rogue’ fractures, induced in fracking operations for shale gas extraction, extending beyond 0.6 kilometres from the injection source is exceptionally low. The probability of fractures extending beyond 350 metres was found to be one per cent.

During fracking operations, fractures are created by drilling and injecting fluid into the rock strata underground to increase oil and gas production from fine-grained, low permeability rocks such as shale. These stimulated fractures can significantly increase the rate of production of oil and gas from such rocks.

Fracking operations in the USA are growing in number and many countries across the world are looking at shale gas as a potential energy resource. The process of fracking has come under increasing scrutiny. A recent test well in the UK near Blackpool, Lancashire, was stopped after some minor earthquakes were felt at the surface. The UK government is allowing the test fracking to resume but critics have also warned of other possible side-effects including the contamination of groundwater.

Researchers from Durham University, Cardiff University and the University of Tromsø looked at thousands of natural and induced fractures from the US, Europe and Africa. Of the thousands artificially induced, none were found to exceed 600 metres, with the vast majority being much less than 250 metres in vertical extent.

Fracture heights are important as fractures have been cited as possible underground pathways for deep sources of methane to contaminate drinking water. But the likelihood of contamination of drinking water in aquifers due to fractures when there is a separation of more than a kilometer is negligible, the scientists say.

Professor Richard Davies, Director of Durham Energy Institute, Durham University, said: “Based on our observations, we believe that it may be prudent to adopt a minimum vertical separation distance for stimulated fracturing in shale reservoirs. Such a distance should be set by regulators; our study shows that for new exploration areas where there is no existing data, it should be significantly in excess of 0.6 km.

“Shale gas exploration is increasing across the world and sediments of different ages are now potential drilling targets. Constraining the maximum vertical extent of hydraulic fractures is important for the safe exploitation of unconventional hydrocarbons such as shale gas and oil, and the data from the USA helps us to understand how fracturing works in practice.

“Minimum vertical separation distances for fracturing operations would help prevent unintentional penetration of shallow rock strata.”

Professor Davies’ team looked at published and unpublished datasets for both natural and stimulated fracture systems in sediment of various ages, from eight different locations in the USA, Europe and Africa.

Professor Richard Davies said: “Sediments of different types and ages are potential future drilling targets and minimum separation depths are an important step towards safer fracturing operations worldwide and tapping into what could be a valuable energy resource.

“We need to keep collecting new data to monitor how far fractures grow in different geological settings.”

The team accepts that predicting the height and behavior of fractures is difficult. They now hope that the oil and gas industry will continue to provide data from new sites across the globe as it becomes available to further refine the probability analysis.

Analysis of new sites should allow a safe separation distance between fracking operations and sensitive rock layers to be further refined, the scientists say. In the meantime, the researchers hope that governments and shale gas drilling companies will use the analysis when planning new operations.

GPS technology used for NASA quake monitoring test

Geoff Blewitt, professor in the University's Nevada Bureau of Mines and Geology and director of the Nevada Geodetic Laboratory, works on a GPS installation atop 8,600-foot-elevation Ward Peak at Lake Tahoe. The Nevada Geodetic Laboratory has the largest GPS data-processing center in the world, which processes information from about 10,000 stations around the globe continuously, 24/7. The system will be used in a major test this year by NASA of a GPS monitoring system for big earthquakes along the West Coast of the United States. -  Photo by Jean Dixon, courtesy of University of Nevada, Reno.
Geoff Blewitt, professor in the University’s Nevada Bureau of Mines and Geology and director of the Nevada Geodetic Laboratory, works on a GPS installation atop 8,600-foot-elevation Ward Peak at Lake Tahoe. The Nevada Geodetic Laboratory has the largest GPS data-processing center in the world, which processes information from about 10,000 stations around the globe continuously, 24/7. The system will be used in a major test this year by NASA of a GPS monitoring system for big earthquakes along the West Coast of the United States. – Photo by Jean Dixon, courtesy of University of Nevada, Reno.

GPS technology developed and implemented at the University of Nevada, Reno will be the centerpiece of a major test this year by NASA to pinpoint the location and magnitude of strong earthquakes along the West Coast of the United States. The project was announced by NASA today.

“We invented the technique to predict tsunamis using GPS, and it will be used in real-time with a network of 500 reporting stations along the West Coast,” said Geoff Blewitt, professor in the University’s Nevada Bureau of Mines and Geology and director of the Nevada Geodetic Laboratory. “This is intended to see abrupt changes in GPS station positions, such as from a great earthquake, though we have recorded movements using GPS in a magnitude 5.0 earthquake – the smallest earthquake ever recorded by GPS.”

The software processes information from satellite reporting stations to show changes in ground positions greater than 10 centimeters in real-time, and processing the next day using better information on the GPS satellite orbits can be extremely accurate, calculating changes as small as one centimeter.

“This allows us to see large rapid ground motions that can then be used to predict tsunamis,” he said.

The NASA monitoring network project runs along the Cascadia fault line that extends from California to Vancouver, Canada and the San Andreas Fault in California. Its development is supported by the National Science Foundation, the Department of Defense, NASA and the U.S. Geological Survey. It is an augmentation of the global monitoring framework developed and maintained by Blewitt and his geodesy team at the University, which was funded by NASA and in concert with the Jet Propulsion Laboratory.

The University of Nevada, Reno has the largest GPS data-processing center in the world, which processes information from about 10,000 stations around the globe continuously, 24/7.

“The information is freely available to anyone on the Internet,” Blewitt said. “We have all GPS data going back to 1996 and are reprocessing all 15-million data files as new data streams come in – every 30 seconds – solving for tens of thousands of parameters at once. It enables real-time positioning for any users.”

“The data is like a gold mine, we keep digging for new discoveries,” he said. “People around the world use it extensively for research such as modeling earthquakes and volcanoes.”

Blewitt is currently presenting results of his team’s research at the European Geosciences Union General Assembly in Vienna, Austria. “Our research has an international impact, and is enabled by strong international collaboration in geodesy,” he said.

Blewitt is teaching a new geodesy course at the University of Nevada, Reno in the fall 2012 semester that is designed for students in physics, geophysics, electrical engineering and geological engineering. The upper-division and graduate-level course, “Special Topics in Physics: Physics and Engineering of GPS,” covers the principles of the GPS for millimeter-precision positioning and sub-nanosecond timing. Topics include: GPS system design, geodesy and the Earth’s changing shape, gravity field and rotation in space, reference systems, satellite orbits, satellite signals, special and general relativity and physical models for positioning.

Warning signs from ancient Greek tsunami

This figure shows the study area in Greece (Thermaikos Gulf). Red stars indicate drilling sites, where researchers have found high-energy layers, which are interpreted a of a tsunami origin. -  Klaus Reicherter, RWTH Aachen University
This figure shows the study area in Greece (Thermaikos Gulf). Red stars indicate drilling sites, where researchers have found high-energy layers, which are interpreted a of a tsunami origin. – Klaus Reicherter, RWTH Aachen University

In the winter of 479 B.C., a tsunami was the savior of Potidaea, drowning hundreds of Persian invaders as they lay siege to the ancient Greek village. New geological evidence suggests that the region may still be vulnerable to tsunami events, according to Klaus Reicherter of Aachen University in Germany and his colleagues.

The Greek historian Herodotus described the strange retreat of the tide and massive waves at Potidaea, making his account the first description of a historical tsunami. Reicherter and colleagues have added to the story by sampling sediments on the Possidi peninsula in northern Greece where Potidaea (and its modern counterpart, Nea Potidea) is located. The sediment cores show signs of “high-energy” marine events like significant waves, and excavations in the suburbs of the nearby ancient city of Mende have uncovered a high-energy level dated to the 5th century B.C. The Mende layer contains much older marine seashells that were probably scoured from the ocean bed and deposited during a tsunami.

Earthquake forecast modeling in the North Aegean Basin near the peninsula suggests that future earthquakes in the area could produce significant tsunami waves, although the area is not included currently in the ten “tsunami” prone regions of Greece. However, Reicherter and colleagues say their new findings suggest the Thermaikos Gulf where the peninsula is located should be included in tsunami hazard calculations, especially since the area is densely populated and home to many holiday resorts.

Reicherter will present his findings at the Annual Meeting of the Seismological Society of America (SSA) on April 19 in San Diego.

Most detailed maps yet of Africa’s groundwater

A scattergun approach to borehole drilling in Africa is likely to be unsuccessful.

This is the message from a group of UK researchers who have, for the first time, quantified the amount, and potential yield, of groundwater across the whole of Africa.

They estimate the total volume of groundwater to be around 0.66 million km3 – more than 100 times the available surface freshwater on the continent – and hope that the assessment can inform plans to improve access to water in Africa, where 300 million people do not have access to safe drinking water.

The results have been published today, 20 April, in IOP Publishing’s journal Environmental Research Letters.

The researchers, from the British Geological Survey and University College London, warn that high yielding boreholes will not be found using a scattergun approach and a more careful and exploratory approach that takes into account local groundwater conditions will be needed, which they hope their new study will encourage.

Their results show that in many populated areas in Africa, there is sufficient groundwater to supply hand pumps that communities can use for drinking water. These hand pumps can deliver around 0.1-0.3 litres per second.

Opportunities for boreholes yielding five litres per second or more – the usual amount needed for commercial irrigation – are not widespread and limited to specific areas, such as countries in the north of Africa.

Central to the researchers’ methods was the collation of existing national hydrogeological maps as well as 283 aquifer studies from 152 publications. The vast amount of data was compiled into a single database in which the researchers were able to make their calculations.

The amount of groundwater present in a certain region is reliant on the interplay between the geology of the area, the amount of weathering and the amount of rainfall experienced both in the past and present. All of these factors were considered to estimate the volume and potential yield of groundwater in each aquifer.

As a result of population growth in Africa and a planned increase in irrigation to meet food demands, water use is set to increase markedly over the next few decades. Climate change will pose a huge threat to this increase; however, groundwater responds much more slowly to increasing climatic variability as opposed to surface water, so will act as a buffer to climate change.

The lead author of the study, Dr Alan MacDonald, said: “Groundwater is such an important water resource in Africa and underpins much of the drinking water supply. Appropriately sited and developed boreholes for low yielding rural water supply and hand pumps are likely to be successful and resilient to climate change.

“High yielding boreholes should not be developed without a thorough understanding of the local groundwater conditions.”

Evidence for a geologic trigger of the Cambrian explosion

The oceans teemed with life 600 million years ago, but the simple, soft-bodied creatures would have been hardly recognizable as the ancestors of nearly all animals on Earth today.

Then something happened. Over several tens of millions of years – a relative blink of an eye in geologic terms – a burst of evolution led to a flurry of diversification and increasing complexity, including the expansion of multicellular organisms and the appearance of the first shells and skeletons.

The results of this Cambrian explosion are well documented in the fossil record, but its cause – why and when it happened, and perhaps why nothing similar has happened since – has been a mystery.

New research shows that the answer may lie in a second geological curiosity – a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments.

“The Great Unconformity is a very prominent geomorphic surface and there’s nothing else like it in the entire rock record,” says Shanan Peters, a geoscience professor at the University of Wisconsin-Madison who led the new work. Occurring worldwide, the Great Unconformity juxtaposes old rocks, formed billions of years ago deep within the Earth’s crust, with relatively young Cambrian sedimentary rock formed from deposits left by shallow ancient seas that covered the continents just a half billion years ago.

Named in 1869 by explorer and geologist John Wesley Powell during the first documented trip through the Grand Canyon, the Great Unconformity has posed a longstanding puzzle and has been viewed – by Charles Darwin, among others – as a huge gap in the rock record and in our understanding of the Earth’s history.

But Peters says the gap itself – the missing time in the geologic record – may hold the key to understanding what happened.

In the April 19 issue of the journal Nature, he and colleague Robert Gaines of Pomona College report that the same geological forces that formed the Great Unconformity may have also provided the impetus for the burst of biodiversity during the early Cambrian.

“The magnitude of the unconformity is without rival in the rock record,” Gaines says. “When we pieced that together, we realized that its formation must have had profound implications for ocean chemistry at the time when complex life was just proliferating.”

“We’re proposing a triggering mechanism for the Cambrian explosion,” says Peters. “Our hypothesis is that biomineralization evolved as a biogeochemical response to an increased influx of continental weathering products during the last stages in the formation of the Great Unconformity.”

Peters and Gaines looked at data from more than 20,000 rock samples from across North America and found multiple clues, such as unusual mineral deposits with distinct geochemistry, that point to a link between the physical, chemical, and biological effects.

During the early Cambrian, shallow seas repeatedly advanced and retreated across the North American continent, gradually eroding away surface rock to uncover fresh basement rock from within the crust. Exposed to the surface environment for the first time, those crustal rocks reacted with air and water in a chemical weathering process that released ions such as calcium, iron, potassium, and silica into the oceans, changing the seawater chemistry.

The basement rocks were later covered with sedimentary deposits from those Cambrian seas, creating the boundary now recognized as the Great Unconformity.

Evidence of changes in the seawater chemistry is captured in the rock record by high rates of carbonate mineral formation early in the Cambrian, as well as the occurrence of extensive beds of glauconite, a potassium-, silica-, and iron-rich mineral that is much rarer today.

The influx of ions to the oceans also likely posed a challenge to the organisms living there. “Your body has to keep a balance of these ions in order to function properly,” Peters explains. “If you have too much of one you have to get rid of it, and one way to get rid of it is to make a mineral.”

The fossil record shows that the three major biominerals – calcium phosphate, now found in bones and teeth; calcium carbonate, in invertebrate shells; and silicon dioxide, in radiolarians – appeared more or less simultaneously around this time and in a diverse array of distantly related organisms.

The time lag between the first appearance of animals and their subsequent acquisition of biominerals in the Cambrian is notable, Peters says. “It’s likely biomineralization didn’t evolve for something, it evolved in response to something – in this case, changing seawater chemistry during the formation of the Great Unconformity. Then once that happened, evolution took it in another direction.” Today those biominerals play essential roles as varied as protection (shells and spines), stability (bones), and predation (teeth and claws).

Together, the results suggest that the formation of the Great Unconformity may have triggered the Cambrian explosion.

“This feature explains a lot of lingering questions in different arenas, including the odd occurrences of many types of sedimentary rocks and a very remarkable style of fossil preservation. And we can’t help but think this was very influential for early developing life at the time,” Gaines says.

Far from being a lack of information, as Darwin thought, the gaps in the rock record may actually record the mechanism as to why the Cambrian explosion occurred in the first place, Peters says.

“The French composer Claude Debussy said, ‘Music is the space between the notes.’ I think that is the case here,” he says. “The gaps can have more information, in some ways, about the processes driving Earth system change, than the rocks do. It’s both together that give the whole picture.”

Managing the seismic risk posed by wastewater disposal

The debate over hydraulic fracturing has recently focused on the rise in seismicity throughout the primarily stable interior of the United States. These intraplate regions, though not unfamiliar with earthquakes, have been experiencing an increased amount of seismic activity in the last decade. This unusual increase is likely to be caused in part by wastewater disposal practices related to natural gas production. With such a sensitive issue it is important to keep the facts in perspective: No earthquake triggered by fluid injection has ever caused serious injury or significant damage. Moreover, approximately 140,000 wastewater disposal wells have been operating safely and without incident in the U.S. for many decades. Nevertheless, minor seismicity can occur, and it is important to recognize that with proper planning, monitoring and response the occurrence of small-to-moderate earthquakes associated with fluid injection can be reduced and the risks associated with such events effectively managed.

What steps can we take in order to safely practice wastewater injection? In the April issue of EARTH Magazine, Mark D. Zoback, professor of geophysics at Stanford University puts forward five steps that can be taken to reduce the probability of triggering seismicity associated with fluid injection. Zoback argues that through proper study and planning prior to injection, careful monitoring in areas where seismicity might be triggered, and careful training of operators and regulators will help to manage the seismic risk posed by wastewater disposal. To learn more, read the full article online at http://www.earthmagazine.org/article/managing-seismic-risk-posed-wastewater-disposal.

Read this story and more in the April issue of EARTH magazine, available online at http://www.earthmagazine.org/. Explore the archaeology, volcanoes and hot springs of the Northern Atacama Desert; Probe the limits of the solar system with Voyager 1; and, unearth the mechanics of crustal thinning.

Study shows Greenland may be slip-sliding away due to surface lake melt

This is a surface or 'supraglacial' lake on the Greenland Ice Sheet. -  Konrad Steffen, University of Colorado
This is a surface or ‘supraglacial’ lake on the Greenland Ice Sheet. – Konrad Steffen, University of Colorado

Like snow sliding off a roof on a sunny day, the Greenland Ice Sheet may be sliding faster into the ocean due to massive releases of meltwater from surface lakes, according to a new study by the University of Colorado Boulder-based Cooperative Institute for Research in Environmental Sciences.

Such lake drainages may affect sea-level rise, with implications for coastal communities, according to the researchers. “This is the first evidence that Greenland’s ‘supraglacial’ lakes have responded to recent increases in surface meltwater production by draining more frequently, as opposed to growing in size,” says CIRES research associate William Colgan, who co-led the new study with CU-Boulder computer science doctoral student Yu-Li Liang.

During summer, meltwater pools into lakes on the ice sheet’s surface. When the water pressure gets high enough, the ice fractures beneath the lake, forming a vertical drainpipe, and “a huge burst of water quickly pulses through to the bed of the ice sheet,” Colgan said.

The study is being published online today by the journal Remote Sensing of the Environment. The study was funded by the Arctic Sciences Program of the National Science Foundation.

The researchers used satellite images along with innovative feature-recognition software to monitor nearly 1,000 lakes on a Connecticut-sized portion of the ice sheet over a 10-year period. They discovered that as the climate warms, such catastrophic lake drainages are increasing in frequency. Catastrophic lake drainages were 3.5 times more likely to occur during the warmest years than the coldest years.

During a typical catastrophic lake drainage, about 1 million cubic meters of meltwater — which is equivalent to the volume of about 4,000 Olympic swimming pools — funnels to the ice sheet’s underside within a day or two. Once the water reaches the ice sheet’s belly that abuts underlying rock, it may turn the ice-bed surface into a Slip ‘N Slide, lubricating the ice sheet’s glide into the ocean. This would accelerate the sea-level rise associated with climate change.

Alternatively, however, the lake drainages may carve out sub-glacial “sewers” to efficiently route water to the ocean. “This would drain the ice sheet’s water, making less water available for ice-sheet sliding,” Colgan said. That would slow the ice sheet’s migration into the ocean and decelerate sea-level rise.

“Lake drainages are a wild card in terms of whether they enhance or decrease the ice sheet’s slide,” Colgan said. Finding out which scenario is correct is a pressing question for climate models and for communities preparing for sea-level change, he said.

For the study, the researchers developed new feature-recognition software capable of identifying supraglacial lakes in satellite images and determining their size and when they appear and disappear. “Previously, much of this had to be double-checked manually,” Colgan said. “Now we feed the images into the code, and the program can recognize whether a feature is a lake or not, with high confidence and no manual intervention.”

Automating the process was vital since the study looked at more than 9,000 images. The researchers verified the program’s accuracy by manually looking at about 30 percent of the images over 30 percent of the study area. They found that the algorithm — a step-by-step procedure for calculations — correctly detected and tracked 99 percent of supraglacial lakes.

The program could be useful in future studies to determine how lake drainages affect sea-level rise, according to the researchers. CIRES co-authors on the team include Konrad Steffen, Waleed Abdalati, Julienne Stroeve and Nicolas Bayou.

Cary Institute Hydrofracking Forum

On Saturday, May 5th from 9AM to noon join the Cary Institute of Ecosystem Studies in Millbrook, N.Y. for a special forum exploring hydrofracking. The event’s goal is to provide citizens and decision makers with current information on the natural gas extraction technique, which involves injecting a high-pressure mix of chemically treated water and sand thousands of feet underground to release gas trapped in shale.

Hydrofracking has been the focus of environmental and economic discussions in New York State, with conversations centering on the future of the Marcellus Shale formation. There is currently a moratorium on hydrofracking in New York, while a task force appointed by the governor investigates the economic and environmental impacts of the drilling practice. Several of the speakers are from Pennsylvania-where hydrofracking in the Marcellus Shale is already underway; one sits on the peer-review panel for the EPA’s hydrofracking study.

Topics to be covered include groundwater contamination, the treatment of hydrofracking wastewater, human health effects, industry innovations, and the social impact that rapid gas booms have on small communities.

Speakers will include:

  • William Schlesinger, Ph.D., President, Cary Institute, Introduction

  • Avner Vengosh, Ph.D., Nicholas School of the Environment, Duke University, Methane and Water Contamination Associated with Shale Gas Development and Hydrofracking
  • Radisav Vidic, Ph.D., P.E., Chairman of the Department of Civil and Environmental Engineering, University of Pittsburgh, Wastewater Quality, Quantity, and Management: Lessons from the Marcellus Shale Region
  • Bernard Goldstein, M.D., Dean Emeritus, University of Pittsburgh Graduate School of Public Health, Potential Public Health Impacts of Hydraulic Fracturing
  • Mark Boling, J.D., Executive Vice President and General Counsel of Southwestern Energy, Hydraulic Fracturing Operations-Separating Fact from Fiction
  • Simona Perry, Ph.D., Science and Technology Studies, Rensselaer Polytechnic Institute, Rapid Shale Gas Developments and Stress Factors in Northern Appalachian Communities
  • Emma Rosi-Marshall, Ph.D., Aquatic Ecologist, Cary Institute; Moderator, Q&A Session

Free and open to the public, the event will be held in the Cary Institute’s auditorium, located at 2801 Sharon Turnpike (Rte. 44) in Millbrook, New York. RSVP is required, name tags will be provided at sign in. Information and registration is available online at: http://www.caryinstitute.org/fracking.html.

Volcanic plumbing provides clues on eruptions and earthquakes

Two new studies into the “plumbing systems” that lie under volcanoes could bring scientists closer to understanding plate ruptures and predicting eruptions-both of which are important steps for protecting the public from earthquake and volcanic hazards.

International teams of researchers, including two scientists from the University of Rochester, have been studying the location and behaviour of magma chambers on the Earth’s mid-ocean ridge system-a vast chain of volcanoes along which the Earth forms new crust.

They worked in the tropical region of Afar, Ethiopia and the subarctic country of Iceland-the only places where mid-ocean ridges appear above sea level. Volcanic ridges (or “spreading centers”) occur when tectonic plates “rift” or pull apart. This happens when magma (hot molten rock) injects itself into weaknesses in the brittle upper crust, erupting as lava and forming new crust upon cooling.

“These conclusions would not have been possible without the multi-disciplinary expertise of the researchers taking part in these studies,” said Cynthia Ebinger, professor of geophysics at the University of Rochester.

The studies, published in Nature Geoscience, reveal new information about where magma is stored and how it moves through the geological plumbing network.

Magma chambers work like plumbing systems, channelling pressurized magma through networks of underground “pipes.” Finding out where magma chambers lie and how they behave could help identify early warning signs of impending eruptions, according to the researchers.

By analyzing images taken by the European Space Agency satellite Envisat, scientists were able to measure how the ground moved before, during, and after eruptions. Also, Ebinger and Manahloh Belachew, also from the University of Rochester, operated an array of seismographs that provided the depth and detailed time control to gauge the fracturing of the earth and the flow of magma from multiple eruptions in Afar. Using these data, the international team built and tested computer models to find out how rifting occurs.

The team of scientists discovered that the ground started “uplifting” (elevating) four months before the eruption, due to new magma increasing pressure in one of the underground chambers. They hope the ground movement will prove to be precursory signals that are fundamental to predicting eruptions.

In an extensive study of eruptions in Afar and Iceland-two vastly different environments-Ebinger and Belachew found remarkable similarities, with many events occurring within a short space of time. They identified multiple magma chambers positioned horizontally and vertically, allowing magma to shoot in several directions. Earthquake patterns were used to track the migrating magma as it inflated cracks, and to map the rupture of faults above the miles of propagating magma injection zones. The combined data sets show that separate magma chambers fed single eruptions.

A sequence of eruptions in Afar from 2005 to the present is part of an unusual period of volcanic unrest in Ethiopia, and is enabling scientists to learn more about magma plumbing systems at spreading centers. Most spreading centers are about a mile under water at the bottom of the ocean, making detailed observations extremely challenging.

“Our studies in Ethiopia open the door to new discoveries of multi-tiered magma chambers along submerged mid-ocean ridges worldwide,” said Ebinger. “We also found that magma movement and faulting during intense episodes create much of the characteristic rift valley topography, where narrow lowlands are found between mountain ranges.”

When magma intrudes into a region it generates earthquakes, according to Belachew, a Ph.D. candidate. “The detailed relations of the earthquake sequences in both time and space allow us to track the movement of magma and associated fault rupture with unprecedented detail,” he said.

Tim Wright, from the University of Leeds’ School of Earth and Environment, heads the international Afar Rift Consortium. “The dramatic events we have been witnessing in Afar in the past six years are transforming our understanding of how the crust grows when tectonic plates pull apart,” said Wright. “Our work in one of the hottest places on Earth is having a direct impact on our understanding of eruptions from the frozen volcanoes of Iceland.”