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.

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.”