New study determines more accurate method to date tropical glacier moraines

The Quelccaya Ice Cap, the world's largest tropical ice sheet, is rapidly melting. -  Meredith Kelly
The Quelccaya Ice Cap, the world’s largest tropical ice sheet, is rapidly melting. – Meredith Kelly

A Dartmouth-led team has found a more accurate method to determine the ages of boulders deposited by tropical glaciers, findings that will likely influence previous research of how climate change has impacted ice masses around the equator.

The study appears in the journal Quaternary Geochronology. A PDF of the study is available on request.

Scientists use a variety of dating methods to determine the ages of glacial moraines around the world, from the poles where glaciers are at sea level to the tropics where glaciers are high in the mountains. Moraines are sedimentary deposits that mark the past extents of glaciers. Since glaciers respond sensitively to climate, especially at high latitudes and high altitudes, the timing of glacial fluctuations marked by moraines can help scientists to better understand past climatic variations and how glaciers may respond to future changes.

In the tropics, glacial scientists commonly use beryllium-10 surface exposure dating. Beryllium-10 is an isotope of beryllium produced when cosmic rays strike bedrock that is exposed to air. Predictable rates of decay tell scientists how long ago the isotope was generated and suggest that the rock was covered in ice before then. Elevation, latitude and other factors affect the rate at which beryllium-10 is produced, but researchers typically use rates taken from calibration sites scattered around the globe rather than rates locally calibrated at the sites being studied.

The Dartmouth-led team looked at beryllium-10 concentrations in moraine boulders deposited by the Quelccaya Ice Cap, the largest ice mass in the tropics. Quelccaya, which sits 18,000 feet above sea level in the Peruvian Andes, has retreated significantly in recent decades. The researchers determined a new locally calibrated production rate that is at least 11 percent to 15 percent lower than the traditional global production rate.

“The use of our locally calibrated beryllium-10 production rate will change the surface exposure ages reported in previously published studies at low latitude, high altitude sites and may alter prior paleoclimate interpretations,” said Assistant Professor Meredith Kelly, the study’s lead author and a glacial geomorphologist at Dartmouth.

The new production rate yields beryllium-10 ages that are older than previously reported, which means the boulders were exposed for longer than previously estimated. Prior studies suggested glaciers in the Peruvian Andes advanced during early Holocene time 8,000 -10,000 years ago, a period thought to have been warm but perhaps wet in the Andes. But the new production rate pushes back the beryllium-10 ages to 11,000 -12,000 years ago when the tropics were cooler and drier. Also during this time, glaciers expanded in the northern hemisphere, which indicates a relationship between the climate mechanisms that caused cooling in the northern hemisphere and southern tropics.

The findings suggest the new production rate should be used to deliver more precise ages of moraines in low-latitude, high-altitude locations, particularly in the tropical Andes. Such precision can help scientists to more accurately reconstruct past glacial and climatic variations, Kelly said.

The oldest ice core

<IMG SRC="/Images/571096301.jpg" WIDTH="350" HEIGHT="278" BORDER="0" ALT="This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn”>
This shows Antarctic locations (in bright blue) where 1.5 million years old ice could exist. The figure is modified from Van Liefferinge and Pattyn (Climate of the Past, 2013). – Van Liefferinge and Pattyn

How far into the past can ice-core records go? Scientists have now identified regions in Antarctica they say could store information about Earth’s climate and greenhouse gases extending as far back as 1.5 million years, almost twice as old as the oldest ice core drilled to date. The results are published today in Climate of the Past, an open access journal of the European Geosciences Union (EGU).

By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere. This, in turn, allows them to make better predictions about how climate will change in the future.

“Ice cores contain little air bubbles and, thus, represent the only direct archive of the composition of the past atmosphere,” says Hubertus Fischer, an experimental climate physics professor at the University of Bern in Switzerland and lead author of the study. A 3.2-km-long ice core drilled almost a decade ago at Dome Concordia (Dome C) in Antarctica revealed 800,000 years of climate history, showing that greenhouse gases and temperature have mostly moved in lockstep. Now, an international team of scientists wants to know what happened before that.

At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago. “The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet,” says Fischer. The Earth’s climate naturally varies between times of warming and periods of extreme cooling (ice ages) over thousands of years. Before the transition, the period of variation was about 41 thousand years while afterwards it became 100 thousand years. “The reason for this change is not known.”

Climate scientists suspect greenhouse gases played a role in forcing this transition, but they need to drill into the ice to confirm their suspicions. “The information on greenhouse-gas concentrations at that time can only be gained from an Antarctic ice core covering the last 1.5 million years. Such an ice core does not exist yet, but ice of that age should be in principle hidden in the Antarctic ice sheet.”

As snow falls and settles on the surface of an ice sheet, it is compacted by the weight of new snow falling on top of it and is transformed into solid glacier ice over thousands of years. The weight of the upper layers of the ice sheet causes the deep ice to spread, causing the annual ice layers to become thinner and thinner with depth. This produces very old ice at depths close to the bedrock.

However, drilling deeper to collect a longer ice core does not necessarily mean finding a core that extends further into the past. “If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away,” Fischer explains. “This is what happens at Dome C and limits its age to 800,000 years.”

To complicate matters further, horizontal movements of the ice above the bedrock can disturb the bottommost ice, causing its annual layers to mix up.

“To constrain the possible locations where such 1.5 million-year old – and in terms of its layering undisturbed – ice could be found in Antarctica, we compiled the available data on climate and ice conditions in the Antarctic and used a simple ice and heat flow model to locate larger areas where such old ice may exist,” explains co-author Eric Wolff of the British Antarctic Survey, now at the University of Cambridge.

The team concluded that 1.5 million-year old ice should still exist at the bottom of East Antarctica in regions close to the major Domes, the highest points on the ice sheet, and near the South Pole, as described in the new Climate of the Past study. These results confirm those of another study, also recently published in Climate of the Past.

Crucially, they also found that an ice core extending that far into the past should be between 2.4 and 3-km long, shorter than the 800,000-year-old core drilled in the previous expedition.

The next step is to survey the identified drill sites to measure the ice thickness and temperature at the bottom of the ice sheet before selecting a final drill location.

“A deep drilling project in Antarctica could commence within the next 3-5 years,” Fischer states. “This time would also be needed to plan the drilling logistically and create the funding for such an exciting large-scale international research project, which would cost around 50 million Euros.”

West Antarctica ice sheet existed 20 million years earlier than previously thought

Adelie penguins walk in file on sea ice in front of US research icebreaker Nathaniel B. Palmer in McMurdo Sound. -  John Diebold
Adelie penguins walk in file on sea ice in front of US research icebreaker Nathaniel B. Palmer in McMurdo Sound. – John Diebold

The results of research conducted by professors at UC Santa Barbara and colleagues mark the beginning of a new paradigm for our understanding of the history of Earth’s great global ice sheets. The research shows that, contrary to the popularly held scientific view, an ice sheet on West Antarctica existed 20 million years earlier than previously thought.

The findings indicate that ice sheets first grew on the West Antarctic subcontinent at the start of a global transition from warm greenhouse conditions to a cool icehouse climate 34 million years ago. Previous computer simulations were unable to produce the amount of ice that geological records suggest existed at that time because neighboring East Antarctica alone could not support it. The findings were published today in Geophysical Research Letters, a journal of the American Geophysical Union.

Given that more ice grew than could be hosted only on East Antarctica, some researchers proposed that the missing ice formed in the northern hemisphere, many millions of years before the documented ice growth in that hemisphere, which started about 3 million years ago. But the new research shows it is not necessary to have ice hosted in the northern polar regions at the start of greenhouse-icehouse transition.

Earlier research published in 2009 and 2012 by the same team showed that West Antarctica bedrock was much higher in elevation at the time of the global climate transition than it is today, with much of its land above sea level. The belief that West Antarctic elevations had always been low lying (as they are today) led researchers to ignore it in past studies. The new research presents compelling evidence that this higher land mass enabled a large ice sheet to be hosted earlier than previously realized, despite a warmer ocean in the past.

“Our new model identifies West Antarctica as the site needed for the accumulation of the extra ice on Earth at that time,” said lead author Douglas S. Wilson, a research geophysicist in UCSB’s Department of Earth Science and Marine Science Institute. “We find that the West Antarctic Ice Sheet first appeared earlier than the previously accepted timing of its initiation sometime in the Miocene, about 14 million years ago. In fact, our model shows it appeared at the same time as the massive East Antarctic Ice Sheet some 20 million years earlier.”

Wilson and his team used a sophisticated numerical ice sheet model to support this view. Using their new bedrock elevation map for the Antarctic continent, the researchers created a computer simulation of the initiation of the Antarctic ice sheets. Unlike previous computer simulations of Antarctic glaciation, this research found the nascent Antarctic ice sheet included substantial ice on the subcontinent of West Antarctica. The modern West Antarctic Ice Sheet contains about 10 percent of the total ice on Antarctica and is similar in scale to the Greenland Ice Sheet.

West Antarctica and Greenland are both major players in scenarios of sea level rise due to global warming because of the sensitivity of the ice sheets on these subcontinents. Recent scientific estimates conclude that global sea level would rise an average of 11 feet should the West Antarctic Ice Sheet melt. This amount would add to sea level rise from the melting of the Greenland ice sheet (about 24 feet).

The UCSB researchers computed a range of ice sheets that consider the uncertainty in the topographic reconstructions, all of which show ice growth on East and West Antarctica 34 million years ago. A surprising result is that the total volume of ice on East and West Antarctica at that time could be more than 1.4 times greater than previously realized and was likely larger than the ice sheet on Antarctica today.

“We feel it is important for the public to know that the origins of the West Antarctic Ice Sheet are under increased scrutiny and that scientists are paying close attention to its role in Earth’s climate now and in the past,” concluded co-author Bruce Luyendyk, UCSB professor emeritus in the Department of Earth Science and research professor at the campus’s Earth Research Institute.

NASA data reveals mega-canyon under Greenland Ice Sheet

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

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

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

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

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

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

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

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

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

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

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

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




Video
Click on this image to view the .mp4 video
Hidden for all of human history, a 460-mile-long canyon has been discovered below Greenland’s ice sheet. Using radar data from NASA’s Operation IceBridge and other airborne campaigns, scientists led by a team from the University of Bristol found the canyon runs from near the center of the island northward to the fjord of the Petermann Glacier.

A large portion of the data was collected by IceBridge from 2009 through 2012. One of the mission’s scientific instruments, the Multichannel Coherent Radar Depth Sounder, operated by the Center for the Remote Sensing of Ice Sheets at the University of Kansas, can see through vast layers of ice to measure its thickness and the shape of bedrock below.

This is a narrated version of an animation that can be found, along with more detailed information, here:

Greenland’s Mega-Canyon beneath the Ice Sheet (id 4097) – NASA SVS

Geochemical ‘fingerprints’ leave evidence that megafloods eroded steep gorge

This 2005 image shows a concentration of grains of zircon taken from sand deposits, where it occurs with other heavy minerals such as magnetite and ilmenite. -  U.S. Geological Survey
This 2005 image shows a concentration of grains of zircon taken from sand deposits, where it occurs with other heavy minerals such as magnetite and ilmenite. – U.S. Geological Survey

The Yarlung-Tsangpo River in southern Asia drops rapidly through the Himalaya Mountains on its way to the Bay of Bengal, losing about 7,000 feet of elevation through the precipitously steep Tsangpo Gorge.

For the first time, scientists have direct geochemical evidence that the 150-mile long gorge, possibly the world’s deepest, was the conduit by which megafloods from glacial lakes, perhaps half the volume of Lake Erie, drained suddenly and catastrophically through the Himalayas when their ice dams failed at times during the last 2 million years.

“You would expect that if a three-day long flood occurred, there would be some pretty significant impacts downstream,” said Karl Lang, a University of Washington doctoral candidate in Earth and space sciences.

In this case, the water moved rapidly through bedrock gorge, carving away the base of slopes so steep they already were near the failure threshold. Because the riverbed through the Tsangpo Gorge is essentially bedrock and the slope is so steep and narrow, the deep flood waters could build enormous speed and erosive power.

As the base of the slopes eroded, areas higher on the bedrock hillsides tumbled into the channel, freeing microscopic grains of zircon that were carried out of the gorge by the fast-moving water and deposited downstream.

Uranium-bearing zircon grains carry a sort of geochemical signature for the place where they originated, so grains found downstream can be traced back to the rocks from which they eroded. Lang found that normal annual river flow carries about 40 percent of the grains from the Tsangpo Gorge downstream. But grains from the gorge found in prehistoric megaflood deposits make up as much as 80 percent of the total.

He is the lead author of a paper documenting the work published in the September edition of Geology. Co-authors are Katharine Huntington and David Montgomery, both UW faculty members in Earth and space sciences.

The Yarlung-Tsangpo is the highest major river in the world. It begins on the Tibetan Plateau at about 14,500 feet, or more than 2.5 miles, above sea level. It travels more than 1,700 miles, crossing the plateau and plunging through the Himalayas before reaching India’s Assam Valley, where it becomes the Brahmaputra River. From there it continues its course to the Ganges River delta and the Bay of Benga

At the head of the Tsangpo Gorge, the river makes a sharp bend around Namche Barwa, a 25,500-foot peak that is the eastern anchor of the Himalayas. Evidence indicates that giant lakes were impounded behind glacial dams farther inland from Namche Barwa at various times during the last 2.5 million years ago.

Lang matched zircons in the megaflood deposits far downstream with zircons known to come only from Namche Barwa, and those signature zircons turned up in the flood deposits at a much greater proportion than they would in sediments from normal river flows. Finding the zircons in deposits so far downstream is evidence for the prehistoric megafloods and their role in forming the gorge.

Lang noted that a huge landslide in early 2000 created a giant dam on the Yiggong River, a tributary of the main river just upstream from the Gorge. The dam failed catastrophically in June 2000, triggering a flood that caused numerous fatalities and much property damage downstream.

That provided a vivid, though much smaller, illustration of what likely occurred when large ice dams failed millions of years ago, he said. It also shows the potential danger if humans decide to build dams in that area for hydroelectric generation.

“We are interested in it scientifically, but there is certainly a societal element to it,” Lang said. “This takes us a step beyond speculating what those ancient floods did. There is circumstantial evidence that, yes, they did do a lot of damage.”

The process in the Tsangpo Gorge is similar to what happened with Lake Missoula in Western Montana 12,000 to 15,000 years ago. That lake was more than 10,000 feet lower in elevation than lakes associated with the Tsangpo Gorge, though its water discharge was 10 times greater. Evidence suggests that Lake Missoula’s ice dam failed numerous times, unleashing a torrent equal to half the volume of Lake Michigan across eastern Washington, where it carved the Channeled Scablands before continuing down the Columbia River basin.

“This is a geomorphic process that we know shapes the landscape, and we can look to eastern Washington to see that,” Lang said.

River deep, mountain high — new study reveals clues to lifecycle of worlds iconic mountains

This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. -  Mike Sandiford University of Melbourne
This image shows the very steep topography of East Timor. The evolution of this mountain range is dominated by ongoing feedbacks between landslides and river erosion. – Mike Sandiford University of Melbourne

Scientists have discovered the reasons behind the lifespan of some of the world’s iconic mountain ranges.

The study conducted by the University of Melbourne, Australia, and Aarhus University, Denmark, has revealed that interactions between landslides and erosion, caused by rivers, explains why some mountain ranges exceed their expected lifespan.

Co-author Professor Mike Sandiford of the School of Earth Sciences at the University of Melbourne said the study had answered the quandary as to why there was fast erosion in active mountain ranges in the Himalayas and slow erosion in others such as the Great Dividing Range in Australia or the Urals in Russia.

“We have shown that links between landslides and rivers are important in maintaining erosion in active or ancient mountain ranges,” he said.

“This study is a great insight into the origins and topography of our globe’s mountainous landscape.”

Mountain ranges are expected to erode away in the absence of tectonic activity but several ranges, such as the Appalachians in the US and the Urals in Russia, have been preserved over several hundred million years.

Co-author, Professor David Egholm from Aarhus University said the new model study published in Nature today provided a plausible mechanism for the preservation of tectonically inactive mountain ranges.

“Computational simulations performed for the study revealed that variations in mountain erosion may relate to a coupling between river incision and landslides,” he said.

Researchers said rivers can cut through bedrock and this process is thought to be the major factor in controlling mountain erosion, however, the long-term preservation of some mountains is at odds with some of the underlying assumptions regarding river erosion rates in current models of river-based landscape evolution.

The study revealed landslides affected river erosion rates in two ways. Large landslides overwhelm river transport capacity and can protect the riverbed from further erosion; conversely, landslides also deliver abrasive agents to the streams, thereby accelerating erosion.

Feedback between these processes can help to stabilize the rates of erosion and increase the lifespan of mountains, the authors said.

As ice melts, Antarctic bedrock is on the move

Eric Kendrick, a senior research associate at Ohio State, shown at a POLENET GPS site in West Antarctica.  He is standing in front of solar panels, battery boxes, and wind generators used to power the GPS station. -  Photo courtesy of Ohio State University
Eric Kendrick, a senior research associate at Ohio State, shown at a POLENET GPS site in West Antarctica. He is standing in front of solar panels, battery boxes, and wind generators used to power the GPS station. – Photo courtesy of Ohio State University

As ice melts away from Antarctica, parts of the continental bedrock are rising in response — and other parts are sinking, scientists have discovered.

The finding will give much needed perspective to satellite instruments that measure ice loss on the continent, and help improve estimates of future sea level rise.

“Our preliminary results show that we can dramatically improve our estimates of whether Antarctica is gaining or losing ice,” said Terry Wilson, associate professor of earth sciences at Ohio State University.

Wilson reported the research in a press conference Monday, December 15, 2008 at the American Geophysical Union meeting in San Francisco.

These results come from a trio of global positioning system (GPS) sensor networks on the continent.

Wilson leads POLENET, a growing network of GPS trackers and seismic sensors implanted in the bedrock beneath the West Antarctic Ice Sheet (WAIS). POLENET is reoccupying sites previously measured by the West Antarctic GPS Network (WAGN) and the Transantarctic Mountains Deformation (TAMDEF) network.

In separate sessions at the meeting, Michael Bevis, Ohio Eminent Scholar in geodyamics and professor of earth sciences at Ohio State, presented results from WAGN, while doctoral student Michael Willis presented results from TAMDEF.

Taken together, the three projects are yielding the best view yet of what’s happening under the ice.

When satellites measure the height of the WAIS, scientists calculate ice thickness by subtracting the height of the earth beneath it. They must take into account whether the bedrock is rising or falling. Ice weighs down the bedrock, but as the ice melts, the earth slowly rebounds.

Gravity measurements, too, rely on knowledge of the bedrock. As the crust under Antarctica rises, the mantle layer below it flows in to fill the gap. That mass change must be subtracted from Gravity Recovery and Climate Experiment (GRACE) satellite measurements in order to isolate gravity changes caused by the thickening or thinning of the ice.

Before POLENET and its more spatially limited predecessors, scientists had few direct measurements of the bedrock. They had to rely on computer models, which now appear to be incorrect.

“When you compare how fast the earth is rising, and where, to the models of where ice is being lost and how much is lost — they don’t match,” Wilson said. “There are places where the models predict no crustal uplift, where we see several millimeters of uplift per year. We even have evidence of other places sinking, which is not predicted by any of the models.”

A few millimeters may sound like a small change, but it’s actually quite large, she explained. Crustal uplift in parts of North America is measured on the scale of millimeters per year.

POLENET’s GPS sensors measure how much the crust is rising or falling, while the seismic sensors measure the stiffness of the bedrock — a key factor for predicting how much the bedrock will rise in the future.

“We’re pinning down both parts of this problem, which will improve the correction made to the satellite data, which will in turn improve what we know about whether we’re gaining ice or losing ice,” Wilson said. Better estimates of sea level rise can then follow.

POLENET scientists have been implanting sensors in Antarctica since December 2007. The network will be complete in 2010 and will record data into 2012. Selected sites may remain as a permanent Antarctic observational network.

Pyrite deposits across the state may be tied to an Eocene meteor





The Chesapeake Bay - Landsat photo
The Chesapeake Bay – Landsat photo

In 2003, during construction of Interstate 99 in Centre County, Pennsylvania, state road builders hit the mother lode. That’s a bad thing.



At a place called Skytop Mountain, 10 miles west of State College, PennDOT engineers encountered a huge deposit of iron pyrite laced through the sandstone ridge. Exposed to air and water, this highly reactive material became an environmental nightmare, leaching sulfuric acid into a nearby stream and groundwater. Subsequent efforts to contain the damage have so far cost more than $79 million.



What caused this massive — and unexpected — sulfide deposit? Barry Scheetz and his colleague Ryan Mathur pin the blame on a meteor that crashed 35 million years ago smack into Chesapeake Bay.



Scheetz, a professor of materials, civil and nuclear engineering at Penn State and an expert on acid mine drainage, was contracted by PennDOT shortly after the Skytop remediation began, and asked to help predict where such deposits might exist elsewhere around the state.



The first step was analyzing the material at hand. Isotopic tests conducted by Ryan Mathur, a geochemist at nearby Juniata College, showed that the Skytop pyrite was 35 million years old, and was molten (about 400 degrees C) at the time of placement. “It came from the mantle,” Scheetz concluded. So how did it get to the surface?



“You need a competent host,” Scheetz said, meaning a substrate of rock hard enough that “when it fractures and opens up, it stays open.” The sandstone at Skytop fits the bill. The fractures there, called lineaments, formed 250 million years ago when the Appalachian mountains pushed up, and extend all the way to bedrock.


“That’s your plumbing system,” Scheetz said. “And the last thing you need is a driver. So the question becomes, what the hell happened 35 million years ago?”



The answer, he said, is a cataclysmic impact. During the late Eocene epoch, a massive object up to three miles in diameter and moving at 12 miles per second slammed into the coastal shallows of what is now the Tidewater region of Virginia. The evidence for this event, known as the Chesapeake Bay impact crater, runs some 52 miles across and nearly as deep as the Grand Canyon. Hidden under the sediments of the bay, the crater was not even suspected until 1983. Its full extent was not known until the mid-1990s.



“My guess is it probably changed the axis of the Earth,” Scheetz said of the collision. “Everything within a 600-mile radius was utterly destroyed.” The result below the surface was similarly dramatic.



“Have you ever seen pictures of people shooting at jugs of water?” Scheetz asks. “How the water just explodes because of the hydraulic impact? That’s exactly what happened here. This thing hit and this enormous hydraulic pulse surged into the mantle. The fluids that were present there shot up through these pre-existing fractures,” and wound up near the surface at Skytop.



“But it’s not just Skytop,” he said. Scheetz and colleagues have tested samples from nine other deposits, six in nearby Blair and Huntingdon counties, two in York County and one as far away as Montgomery County, in the southeastern part of the state. All have the same isotopic signature. “The fact that we have found 10 of these things tells me they could be anywhere in Pennsylvania,” he said.



He and a graduate student, Chad Ellsworth, have mapped some of the major lineaments in the ridge and valley region, using telltale landscape features like wind and water gaps and the presence of sandstone to locate additional deposits along these fractures. They have mapped 150 known deposits so far — many, Scheetz suspects, have the potential to result from the same wayward meteor. He is looking for funding that would allow him to incorporate aerial reconnaissance and electromagnetic sensing into the search.



“Being able to predict where these isolated deposits are likely to pop up,” he says, “could prevent future Skytops around the state and beyond.”

As A River Runs Through It, A Death Valley Stream Offers Insights Into Flooding And Climate Change





Entrance to Death Valley National Park
Entrance to Death Valley National Park

Death Valley may be known by its three superlatives: hottest, driest, and lowest – as in temperature, rainfall, and elevation in the United States. But it was the flow of water through the National Park that attracted Boston College Asst. Prof. of Geology and Geophysics Noah P. Snyder to the desert of eastern California.



In one of the few places where rivers do not flow to the sea, Snyder’s research into a 1941 stream diversion in the historic park uncovered a rare glimpse into a range of geological changes that might otherwise take centuries to unfold but instead are revealed following the flashfloods that strike the park, located against the Nevada border.



Furnace Creek Wash, diverted to protect a village from flooding during infrequent but powerful rainstorms, has carved through Gower Gulch over the years. The way the creek cuts through the sandy hills highlights the effects original landscape and changing channel dynamics exert on the responses of diverted rivers and streams, according to research by Snyder, published in February edition of the journal Geology.



“This is an unusual opportunity to see how a river system responds to an extreme change in the historic rates of water and sediment flow,” said Snyder, who co-authored the paper with former graduate student Lisa R. Kammer ’05. “It’s a hot topic in the earth sciences where we’re interested in learning more about the interaction of climate change, tectonics and bedrock erosion.”



In response to the diversion, Snyder found the Furnace Creek produced an unusual hybrid of consequences: at some points, the creek cuts into the land, leaving deep slices in the bedrock from the surge of flood waters brought on by as little as a half-inch to an inch of rain falling over the watershed that rolls out of the Funeral Mountains. At other points, where soft, sedimentary rocks sit below the surface, the creek has had a widening effect on its channel. These changes are brought on by periodic storms, not the steady flow of a routinely-fed creek or river, giving Snyder a chance to document this combination of effects at work.



Geologists have established models to predict the responses of channels, particularly bedrock rivers, Snyder said. Until he decided to investigate Gower Gulch, there had been few natural experiments to allow geologists to test and validate the models.


Snyder, who presented some of his findings in December at the annual meeting of the American Geophysical Union, specializes in river habitat restoration and lends his expertise to a number of dam removal projects throughout New England. He said he was drawn to Gower Gulch because of the unique opportunity to measure effects that mimic the impact of climate change on river flooding and erosion.



His research included a field study in the park in 2005, a review of aerial photographs taken between 1948 and 1995, as well as laser-guided elevation data provided by the National Center for Airborne Laser Mapping.



A geological wonder known for its searing summer-time temperatures, Death Valley sits nearly 300 feet below sea level, making it one of the few sites in the U.S. where rivers do not flow to the sea. A small dam and an opening blasted by engineers in 1941 now send Furnace Creek Wash rushing through Gower Gulch before emptying into the valley floor. Gower Gulch, dominated by sculpted sedimentary rock reminiscent of the rutted landscape of the Badlands of South Dakota, was photographed after the diversion by the late naturalist and photographer Ansel Adams.



The creek was diverted to prevent the flooding of a small village, but the National Park continues to sustain damage when heavy rains deluge the region. A flash flood in 2006 swept away vehicles, washed out roads and undermined visitor facilities at the Zabriskie Point look-out, according to park service reports.



Snyder said he does not expect any efforts to return Furnace Creek Wash to its original state because that would probably require relocation of the National Park Service village downstream. But the activity in Gower Gulch provides almost a time-lapse view into the effects of water flow. Under normal conditions, the effects of rivers and streams take eons to clearly manifest themselves in the land. But the man-made diversion, coupled with the intermittent flow of the creek through Gower Gulch has produced a microcosm of geological activity for Snyder and other scientists to observe, Snyder said.



“We would never see anything quite like this in New England, which certainly made this an interesting research project,” Snyder said. “But given the climatic change that has been documented, the potential impact of that change on river floods, and the growing burden placed on waterways around the world, there’s a value in better understanding the dynamics at play as rivers flow naturally or as a result of our intervention.”