US-led international research team confirms Alps-like mountain range exists

Flying twin-engine light aircraft the equivalent of several trips around the globe and establishing a network of seismic instruments across an area the size of Texas, a U.S.-led, international team of scientists has not only verified the existence of a mountain range that is suspected to have caused the massive East Antarctic Ice Sheet to form, but also has created a detailed picture of the rugged landscape buried under more than four kilometers (2.5 miles) of ice.

“Working cooperatively in some of the harshest conditions imaginable, all the while working in temperatures that averaged -30 degrees Celsius, our seven-nation team has produced detailed images of last unexplored mountain range on Earth,” said Michael Studinger, of Columbia University’s Lamont-Doherty Earth Observatory, the co-leader of the U.S. portion of the Antarctica’s Gamburstev Province (AGAP) project. “As our two survey aircraft flew over the flat white ice sheet, the instrumentation revealed a remarkably rugged terrain with deeply etched valleys and very steep mountain peaks.”

The National Science Foundation (NSF), in its role as manager of the U.S. Antarctic Program, provided much of the complex logistical support that made the discoveries possible. NSF also supported U.S. researchers from Columbia University, Washington University in St. Louis, Pennsylvania State University, the Center for Remote Sensing of Ice Sheets (CReSIS) at the University of Kansas, the U.S. Geological Survey (USGS) and the Incorporated Research Institutions in Seismology (IRIS).

The initial AGAP findings–which are based on both the aerogeophysical surveys and on data from a network of seismic sensors deployed as part of the project–while extremely exciting, also raise additional questions about the role of the Gamburtsevs in birthing the East Antarctic Ice Sheet, which extends over more than 10 million square kilometers atop the bedrock of Antarctica, said geophysicist Fausto Ferraccioli, of the British Antarctic Survey (BAS), who led the U.K. science team.

“We now know that not only are the mountains the size of the European Alps but they also have similar peaks and valleys,” he said. “But this adds even more mystery about how the vast East Antarctic Ice Sheet formed.”

He added that “if the ice sheet grew slowly then we would expect to see the mountains eroded into a plateau shape. But the presence of peaks and valleys could suggest that the ice sheet formed quickly–we just don’t know. Our big challenge now is to dive into the data to get a better understanding of what happened” millions of years ago.

The AGAP survey area covered roughly 2 million square kilometers of the ice sheet.

The initial data also appear to confirm earlier findings that a vast aquatic system of lakes and rivers exists beneath the ice sheet of Antarctica, a continent that is the size of the U.S. and Mexico combined.

“The temperatures at our camps hovered around -30 degrees Celsius, but three kilometers beneath us at the bottom of the ice sheet we saw liquid water in the valleys,” said AGAP U.S. Co-leader Robin Bell, also of Lamont Doherty. “The radar mounted on the wings of the aircraft transmitted energy through the thick ice and let us know that it was much warmer at the base of the ice sheet.”

The AGAP data will help scientists to determine the origin of the East Antarctic Ice Sheet and the Gamburtsevs’ role in it. It will also help them to understand the role the subglacial aquatic system plays in the dynamics of ice sheets, which will, in turn, help reduce scientific uncertainties in predictions of potential future sea level rise. The most recent report of the Intergovernmental Panel on Climate Change (IPCC) said that it is difficult to predict how much the vast ice sheets of Greenland and Antarctica will contribute to sea-level rise because so little is known about the behavior of the ice sheets.

The data also will be used to help locate where the world’s oldest ice is located.

The AGAP discoveries were made through fieldwork that took place in December and January, near the official conclusion of the International Polar Year (IPY), the largest coordinated international scientific effort in five decades. Ceremonies marking the conclusion of IPY fieldwork will take place in Geneva, Switzerland on Feb. 25.

NSF is the lead U.S. agency for IPY. Through the Antarctic Program, NSF manages all federally funded research on the southernmost continent.

Fully in the spirit of IPY, noted Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources, teams of scientists, engineers, pilots and support staff from Australia, Canada, China, Germany, Japan, the U.K. and the U.S. pooled their knowledge, expertise and logistical resources to deploy two survey aircraft, equipped with ice-penetrating radar, gravimeters and magnetic sensors as well as the network of seismometers, an effort that no one nation alone could have mounted.

“This is a fantastic finale to IPY,” added Ferraccioli.

Bell meanwhile, noted that AGAP is “emblematic of what the international science community can accomplish when working together.”

In one of the most ambitious, challenging and adventurous ‘deep field’ Antarctic IPY expeditions, AGAP scientists gathered the terabytes of data needed to create images of the enigmatic Gamburtsevs, first discovered by Russian scientists in 1957 during the International Geophysical Year (IGY), the predecessor to IPY.

While the planes made a series of survey flights, covering a total of 120,000 square kilometers, the seismologists flew to 26 different sites throughout an area larger than the state of Texas using Twin Otter aircraft equipped with skis, to install scientific equipment that will run for the next year on solar power and batteries.

The seismology team, from Washington University, Penn State, IRIS, and Japan’s National Institute of Polar Research, also recovered ten seismographs that have been collecting data since last year over the dark Antarctic winter at temperatures as low as -73 degrees Celsius (-100 degrees Fahrenheit).

“The season was a great success,” said Douglas Wiens, of Washington University in St. Louis. “We recovered the first seismic recordings from this entire part of Antarctica, and operated seismographs over the Antarctic winter at temperatures as low as -100 F for the first time. Now, we are poring over the data to find out what is responsible for pushing up mountains in this part of Antarctica.”

Dirty snow causes early runoff in Cascades, Rockies

When soot from pollution settles on pristine snow, it can increase snowmelt in the winter month of February (top left, red) and decrease it in the late spring (May -- bottom right, blue). -  Pacific Northwest National Laboratory
When soot from pollution settles on pristine snow, it can increase snowmelt in the winter month of February (top left, red) and decrease it in the late spring (May — bottom right, blue). – Pacific Northwest National Laboratory

Soot from pollution causes winter snowpacks to warm, shrink and warm some more. This continuous cycle sends snowmelt streaming down mountains as much as a month early, a new study finds. How pollution affects a mountain range’s natural water reservoirs is important for water resource managers in the western United States and Canada who plan for hydroelectricity generation, fisheries and farming.

Scientists at the Department of Energy’s Pacific Northwest National Laboratory conducted the first-ever study of soot on snow in the western states at a scale that predicted impacts along mountain ranges. They found that soot warms up the snow and the air above it by up to 1.2 degrees Fahrenheit, causing snow to melt.

“If we can project the future — how much water we’ll be getting from the rivers and when — then we can better plan for its many uses,” said atmospheric scientist Yun Qian. “Snowmelt can be up to 75 percent of the water supply, in some regions. These changes can affect the water supply, as well as aggravate winter flooding and summer droughts.”

The soot-snow cycle starts when soot, a byproduct of burning fossil fuels, darkens snow it lands upon, which then absorbs more of the sun’s energy than clean white snow. The resulting thinner snowpack reflects less sunlight back into the atmosphere and further warms the area, continuing the snowmelt cycle.

This study revealed regional changes to the snowpack caused by soot, whereas other studies looked at the uniform changes brought by higher air temperatures due to greenhouse gases.

Previous studies have examined the effect of airborne or snowbound soot on global climate and temperatures. Qian and his colleagues at PNNL used a climate computer model to zoom in on the Rocky Mountain, Cascade, and other western United States mountain ranges. They modeled how soot from diesel engines, power plants and other sources affected snowpacks it landed on.

They found that changes to snow’s brightness results in its melting weeks earlier in spring than with pristine snow. In addition, less mountain snow going into late spring means reduced runoff in late spring and summer. They will report their findings in an upcoming issue of the Journal of Geophysical Research — Atmospheres.

Making Snowhills from Mountains

Researchers know that soot settles on snow. And like an asphalt street compared to a concrete sidewalk, dirty snow retains more heat from the sun than bright white snow. Qian and colleagues wanted to determine to what degree dark snow contributes to the declining snowpack.

To get the kind of detail from their computer model that they needed, the PNNL team used a regional model called the Weather Research and Forecasting model — or WRF, developed in part at the National Center for Atmospheric Research in Boulder, Colo. Compared to planet-scale models that can distinguish land features 200 kilometers apart, this computer model zooms in on the landscape, increasing resolution to 15 kilometers. At 15 kilometers, features such as mountain ranges and soot deposition are better defined.

Recently, PNNL researchers added a software component to WRF that models the chemistry of tiny atmospheric particles called aerosols and their interaction with clouds and sunlight. Using the WRF-chem model, the team first examined how much soot in the form of so-called black carbon would land on snow in the Sierra Nevada, Cascade and Rocky Mountains.

Then the team simulated how that soot would affect the snow’s brightness throughout the year. Finally, they translated the brightness into snow accumulation and melting over time.

Gray Outlook

“Earlier studies didn’t talk about snowpack changes due to soot for two reasons,” said atmospheric scientist and co-author William Gustafson. “Soot hasn’t been widely measured in snowpack, and it’s hard to accurately simulate snowpack in global models. The Cascades have lost 60 percent of their snowpack since the 1950s, most of that due to rising temperatures. We wanted to see if we could quantify the impact of soot.”

Their simulations compared well to data collected on snowpack distribution and water runoff. But their first experiment did not include all sources of soot, so they modeled what would happen if enough soot landed on snow to double the loss of brightness. In this computer simulation, the regional climate and snowpack changed significantly, and not in a simply predictable way.

Overall, doubling the dimming of the snow did not lead to twice as high temperature changes — it led to an approximate 50 percent increase in the snow surface temperature. The drop in snow accumulation, however, more than doubled in some areas. Snowpack over the central Rockies and southern Alberta, for example, dropped two to 50 millimeters over the mountains during late spring and early winter. The most drastic changes occurred in March, the model showed.

The team also found that soot decreased snow’s brightness in two ways. About half of soot’s effect came from its dark color. The other half came indirectly from reducing the size of the snowpack, exposing the underlying darker earth.

Studies like this one start to unmask pollution’s role in the changing climate. While greenhouse gases work unseen, soot bares its dark nature, with a cloak that slowly steals summertime’s snow.

Glacial erosion changes internal mountain structure, responses to plate tectonics

A network of these devises was deployed as part of the STEEP program in order to record, characterize, and locate the numerous earthquakes related to the St. Elias orogen each year. -  Photograph taken by Aaron L. Berger in 2006
A network of these devises was deployed as part of the STEEP program in order to record, characterize, and locate the numerous earthquakes related to the St. Elias orogen each year. – Photograph taken by Aaron L. Berger in 2006

Intense glacial erosion has not only carved the surface of the highest coastal mountain range on earth, the spectacular St. Elias range in Alaska, but has elicited a structural response from deep within the mountain.

This interpretation of structural response is based on real-world data now being reported, which supports decades of model simulations of mountain formation and evolution regarding the impact of climate on the distribution of deformation associated with plate tectonics.

A team of researchers from seven universities report the results of their field studies, on the structural response of the St. Elias range to glacial erosion, in Nature Geosciences*. The paper was a partnership of Aaron L. Berger, whose Ph.D. research it encompassed, his major professor, James A. Spotila, both with the Virginia Tech geosciences department; Sean P.S. Gulick of the Institute for Geophysics, Jackson School of Geosciences, at the University of Texas at Austin; and other colleagues. Berger and Spotila headed the land-based erosion research team. Gulick headed the ocean-based seismic reflection and sedimentation research team. The project is part of the National Science Foundation-funded St. Elias Erosion-Tectonics Project (STEEP), lead by Terry L. Pavlis of the University of Texas, El Paso.

The St. Elias range is a result of 10 million years of the North American plate pushing material up as it overrides the Pacific plate, then the material being worn down by glaciers. A dramatic cooling across the earth about three million years ago resulted in the onset of widespread glaciation. A million years ago, glacial conditions became more intense and glaciers grew larger over longer periods, and transitioned into more erosive ice streams that changed the shape and evolution of the mountains. The process continues today, resulting in the particularly active and dramatic St. Elias “orogen” – geologists’ word for mountains that grow from collision of tectonic plates.

“The collisions of tectonic plates over millions of years leave a record in the sediments, but it is a history that is difficult to extract. The signals of the impact of climate are even more difficult to track. Which is why scientists have used mathematical models,” said Spotila.

Models create a simplified numeric version of an orogen. Then scientists can change variables in the mathematical formula to determine what happens as a result of climate – whether rain or glaciers. “Models are important in that they showed us that climate change can effect mountain growth,” Spotila said. “And the St. Elias orogen behaves very differently than ones that are at lower latitudes and receive most of their precipitation as rain,” he said.

Armed with the insight of the models, Spotila, his Virginia Tech students, and colleagues at other universities have braved the mountain over many years to collect physical evidence. They have been dropped in remote and dangerous locations by helicopter to place instruments and collect samples to determine bedrock cooling rates and sedimentation.

“But our data set wouldn’t have shown the complete picture,” said Spotila. “We looked at the erosion history onshore and Gulick’s team looked at the record off shore – the shelf where the eroded sediment rest.”

Offshore seismic and borehole data indicate that the increase in offshore sedimentation corresponds to a one-million-year ago change in glaciation and deformation.

How does a change of the mountain surface result in a change of its internal structure? Spotila explained, “If you push snow with a plow, it will always pile up in front of the plow with the same shape,” called the Coulomb wedge when applied to the making of mountains. As the North America plate slips over the Pacific plate, it piles up material for the St Elias orogen with a short side toward the plow inland and a long slope down to the ocean, with the toe dipping into the sea.

Enter the glacier. As glacial conditions took hold across the St. Elias orogen, the landscape began to be defined by glacial landforms left on its surface. However, the more extreme glacial cycles, and associated increased erosion, of the last million years pushed the orogen to a tipping point, beyond which the orogen was forced to totally restructure itself, Berger said. There are deformation zones where as much as half of the wedge was removed, the researchers report in the journal article.

Due the onset of accelerated glacial erosion, the St. Elias orogen struggled to maintain its wedge shape. “Rock faulting and folding has become more intense as the orogen internally deforms to adjust to the intensified erosion,” said Spotila. “The flux of rock from the mountains to the sea is increasing dramatically.”

Berger uses an analogy of a bulldozer pushing sand across the ground. “As the glaciers erode the top of the mountains (the top of the pile of sand), the orogen – or entire body of sand, begins readjusting itself internally to maintain its wedge-shape. If you could remove the glaciers and watch the process, the flank of the mountain range where the largest glaciers are located would begin to get planed away by erosion, reducing mean elevation. The removal of this rock would change the local tectonic stress fields, resulting in focused deformation, which would begin to push the mountains back up to replace the eroded material.”.

The research showed how a change in climate led to a change in the way the motion of tectonic plates is accommodated by structural deformation within the orogen, Spotila said. “The wedge is still present but has narrowed with the eroded material deposited across the toe. Some faults, which previously responded to the push of the plow or tectonic plate, are relocated to respond to the erosion.”

Spotila concludes, “It is remarkable that climate and weather and the atmosphere can have such a profound impact on tectonics and the behavior of the solid earth.”

Origin of Alps-size Antarctic mountain range unknown

A U.S.-led, multinational team of scientists this month will investigate one of the Earth’s last major unexplored places, using sophisticated airborne radar and ground-based seismologic tools to virtually peel away more than 2.5 miles of ice covering an Antarctic mountain range that rivals the Alps in elevation.

Researchers from Penn State and Washington University in St. Louis will contribute to the fieldwork by using seismic recordings of earthquakes to create images of the crust and mantle beneath the mountain range. Andrew Nyblade, professor of geosciences, Penn State, and Douglas Wiens, professor and chair, Earth and planetary sciences, Washington University, are principal investigators on the Gamburtsev Antarctic Mountains Seismic Experiment (GAMSEIS).

The seismic images they obtain will help determine how the mountain range formed. GAMSEIS will deploy an array of 23 stations spread over the mountain range that will gather seismic data.

Current scientific knowledge leads researchers to conclude that the Gamburtsev Mountain range “shouldn’t be there” at all.

The researchers from six nations hope to find answers to questions about the nature of Antarctica and specifically the massive East Antarctic Ice Sheet. Researchers want to know how Antarctica became ice-covered and whether that process began millions of years ago in the enigmatic Gamburtsev Mountain range.

Working daily at extreme altitudes, in 24 hours of sunlight and temperatures as low as minus 40 Fahrenheit, the researchers of the Antarctic Gamburtsev Province (AGAP) team hope they can answer whether the Gamburtsevs were born of tectonic activity in Antarctica or date from a period millions of years ago, when Antarctica was the center of an enormous supercontinent located at far lower latitudes.

Robin Bell, Columbia University’s Lamont-Doherty Earth Observatory, shares the leadership of the U.S. science effort and is in charge of the airborne work. She said AGAP will help scientists understand one of Antarctica’s last major unexplored regions.

“Because the heart of East Antarctica is so difficult to get to we know very little about it,” says Bell. “The Gamburtsev mountain range is fascinating-it defies all geological understanding of how mountains evolve-it really shouldn’t be there.

“We think also that there’s a strong possibility that the mountains are the birthplace of the East Antarctic Ice Sheet. Over 30 million years ago ice began to grow around the peaks, eventually burying the range and its surrounding lakes. I’m really excited that at last we have a chance to find out what happened,” she said.

“For two and a half months our international teams will pool their resources and expertise to survey mountains the size of the Alps buried under the ice sheet that currently defy any reasonable geological explanation,” added Fausto Ferraccioli, geophysicist, British Antarctic Survey, who is leading the United Kingdom’s team. “At the same time, we will hunt for ice that is more than 1.2 million years old. Locked in this ancient ice is a detailed record of past climate change that may assist in making better predictions for our future.”

AGAP, involving researchers and support personnel from Australia, China, Germany, Japan, United Kingdom andUnited States, caps the global scientific deployment known as the International Polar Year (IPY), the largest coordinated international scientific effort in 50 years. The Gamburtsevs were discovered by a Soviet traverse during the last IPY in 1957-58 that was known as the International Geophysical Year.

Traveling deep into the Antarctic interior, roughly 394 miles from the South Pole, the science teams will spend two months at a pair of remote field camps while they complete the first major geophysical survey to map the mysterious landscape.

AGAP fieldwork is emblematic of the scientific goals of the current IPY and of the scientific advances made in the past 50 years because it will use tools and techniques that were simply unavailable in IGY. BAS and NSF aircraft, specially equipped with ice-penetrating radar technology, gravimeter and magnetic field sensors, will fly survey lines over an area more than twice the size of California.

“This project is possible almost uniquely at this point in time because of the international framework created by IPY, which gives researchers from many nations as single common conduit to pool their efforts for the greater scientific good,” said AGAP researcher Detlef Damaske of Germany’s Federal Institute for Geosciences and Natural Resources.

In addition to researchers from the six participating nations, AGAP requires nine aircraft, the establishment of two deep-field science camps, support from U.S. Amundsen-Scott South Pole and McMurdo research stations, the Australian Antarctic Davis Station and the British Antarctic Survey’s Rothera Research Station. Science and support teams on the Chinese tractor train from Zhongshan Station to Dome A will sample ice cores and decommission the UK-Australian Camp. Field depot camps and three other logistics support stations will ensure that food, fuel, supplies and equipment and people are in the right place at the right time.

The U.S. research teams, from Columbia; Penn State; Washington University; the Center for Remote Sensing of Ice Sheets, University of Kansas; Incorporated Research Institutions in Seismology and the U.S. Geological Survey, are supported by the National Science Foundation, which manages all U.S. research on the southernmost continent through the U.S. Antarctic Program. NSF also is the lead U.S. agency for IPY.

Andes Mountains grew in rapid spurts, not slowly, researcher says

Cerro Tronador, Argentina
Cerro Tronador, Argentina

Mountain building may occur in faster fits and spurts than previously realized, according to a new study tracking the uplift of a central portion of the massive Andes Mountains in South America.

Using multiple techniques of geochemical analysis, scientists reconstructed 28 million years of the Altiplano portion of the central Andes’ ancient upward march due to movements in the earth’s tectonic plates miles below. But the peaks didn’t grow slowly and steadily, according to University of Florida researcher Bruce MacFadden, a co-author of the study published June 6 in the journal Science.

“Instead of the Altiplano rising little by little each year, like conventional theory might indicate, we found two cycles of spasmodic or punctuated uplift interspersed by millions of years of stability,” said MacFadden, a vertebrate paleontology curator at the Florida Museum of Natural History.

Geologists have long known mountains are born when continental crust shortens and thickens as one tectonic plate slides beneath another, so conventional theory held that the Altiplano rose gradually in sync with the moving of the earth’s plates. But the study reports an unexpected process. Lead author Carmala Garzione, a geologist at the University of Rochester, said the Nazca tectonic plate sliding beneath the South American continental plate caused the dense lower crust to accumulate material at deep depths.

“But when the dense material is removed rapidly – by downward dripping which is a convective process, or by another process called delamination – it caused rapid surface uplift,” Garzione said. “Our findings will force geologists to acknowledge that removal of lower lithosphere material could be an important process that causes rapid surface uplift in different mountain belts worldwide and over geologic time.”

To reconstruct the Altiplano’s sequential rise, the researchers coaxed geochemical clues in the form of oxygen isotopes from ancient soil nodules made of calcium carbonate. The nodules were sampled from layered soil deposits between 5 million and 28 million years old. Oxygen isotopes serve as reliable proxy indicators for the actual temperatures in which they formed – so the researchers used them to reconstruct ancient temperature records, and then linked these records to known temperature clines associated with vertical elevation gain. They also analyzed magma and sediment as additional proxies.

Dork Sahagian, a professor of earth and environmental sciences at Lehigh University who did not participate in this study, said that while weaknesses were inherent when single proxy methods were used, the multiple methods used in this study made the results robust.

“Remarkably, the rapid recent uplift scenario presented here is similar to what I found for the Colorado Plateau,” Sahagian said. “The greatest novelty in their study is the number of proxies they brought to bear on the problem. This is the right way to go about it.”

In 2005, Sahagian organized a national workshop to refine and strengthen paleoelevation techniques. Garzione presented the beginnings of her Altiplano work there and later, she contacted MacFadden to tap his three decades of research on stratigraphy and fossils from the Bolivian Andes. Over the past few years, MacFadden led Garzione and her team to several key fossil sites in the Altiplano where he had established geological age sequences decades ago. While Garzione’s interest was grounded in geology, MacFadden was interested in understanding how the birth of the Andes may have affected South America’s ancient animals and climate.

“The big-picture question is: When did the Andes grow high enough to become drivers of the South American climatic regime? Because this event obviously had cascading effects upon plant and animal life across the continent,” MacFadden said. “If we could rewind a video of their formation, we’d see how they grew into an immense force, affecting the distribution and abundance of moisture across large portions of South America.”

Today, the Andes’ massive mountain belt snakes 4,400 miles along the continent’s western edge and is the longest unbroken terrestrial chain on the planet, with peaks soaring to 22,841 feet. The world’s driest desert, the Atacama, lies to its east and the world’s largest collection of wetlands form the Pantanal to its west.

Additional study co-authors include: Gregory Hoke, University of Rochester; Julie Libarkin and Saunia Withers, Michigan State University; John Eiler, California Institute of Technology; Prosenjit Ghosh, Center for Atmospheric and Oceanic Science; and Andreas Mulch, Universität Hanover in Germany.

Mountains reached current elevation earlier than thought

The Ruby Mountains, in northeast Nevada, are within the Basin and Range region where Andreas Mulch and his colleagues analyzed samples of volcanic glass. - Photo Credit: Andreas Mulch
The Ruby Mountains, in northeast Nevada, are within the Basin and Range region where Andreas Mulch and his colleagues analyzed samples of volcanic glass. – Photo Credit: Andreas Mulch

Sierra Nevada rose to current height earlier than thought, geologists say

Geologists studying deposits of volcanic glass in the western United States have found that the central Sierra Nevada largely attained its present elevation 12 million years ago, roughly 8 or 9 million years earlier than commonly thought.

The finding has implications not only for understanding the geologic history of the mountain range but for modeling ancient global climates.

“All the global climate models that are currently being used strongly rely on knowing the topography of the Earth,” said Andreas Mulch, who was a postdoctoral scholar at Stanford when he conducted the research. He is the lead author of a paper published this week in the online Early Edition of the Proceedings of the National Academy of Sciences.

A variety of studies over the last five years have shown that the presence of the Sierra Nevada and Rocky Mountains in the western United States has direct implications for climate patterns extending into Europe, Mulch said.

“If we did not have these mountains, we would completely change the climate on the North American continent, and even change mean annual temperatures in central Europe,” he said. “That’s why we need to have some idea of how mountains were distributed over planet Earth in order to run past climate models reliably.” Mulch is now a professor of tectonics and climate at the University of Hannover in Germany.

Mulch and his colleagues, including Page Chamberlain, a Stanford professor of environmental earth system science, reached their conclusion about the timing of the uplift of the Sierra Nevada by analyzing hydrogen isotopes in water incorporated into volcanic glass.

They analyzed volcanic glass at sites from the Coast Ranges bordering the Pacific Ocean, across the Central Valley and the Sierra Nevada and into the Basin and Range region of Nevada and Utah.

The ratio of hydrogen isotopes in the glass reflects changes that occurred to the water vapor content of air over the Pacific Ocean as it blew onto the continent and crossed the Sierra Nevada. As the air gains elevation, it cools, moisture concentrates and condenses, and it rains. Water containing heavier isotopes of hydrogen tends to fall first, resulting in a systematic decrease in the ratio of heavy water molecules to lighter ones in the remaining water vapor.

Because so much of the airborne moisture falls as rain on the windward side of the mountains, land on the leeward side gets far less rain-an effect called a “rain shadow”-which often produces a desert.

The higher the mountain, the more pronounced the rain shadow effect is and the greater the decrease in the number of heavy hydrogen isotopes in the water that makes it across the mountains and falls on the leeward side of the range. By determining the ratio of heavier to lighter hydrogen isotopes preserved in volcanic glass and comparing it with today’s topography and rainwater, researchers can estimate the elevation of the mountains at the time the ancient water crossed them.

Volcanic glass is an excellent material for preserving ancient rainfall. The glass forms during explosive eruptions, when tiny particles of molten rock are ejected into the air. “These glasses were little melt particles, and they cooled so rapidly when they were blown into the atmosphere that they just froze, basically,” Mulch said. “They couldn’t crystallize and form minerals.”

Because glass has an amorphous structure, as opposed to the ordered crystalline structure of minerals, there are structural vacancies in the glass into which water can diffuse. Once the glass has been deposited on the surface of the Earth, rainwater, runoff and near-surface groundwater are all available to interact with it. Mulch said the diffusion process continues until the glass is effectively saturated with water.

Other researchers have shown that once such volcanic glass is fully hydrated, the water in it does not undergo any significant isotopic exchange with its environment. Thus, the trapped water becomes a reliable record of the isotopic composition of the water in the environment at the time the glass was deposited.

“It takes probably a hundred to a thousand years or so for these glasses to fully hydrate,” Mulch said. But 1,000 years is the blink of an eye in geologic time and, for purposes of estimating the timing of events that occur on scales of millions or tens of millions of years, that degree of resolution is quite sufficient.

Likewise, you need deposits of volcanic ash that were laid down relatively quickly over a broad area. But that’s the norm for explosive eruptions. Though some ash may circulate in the upper atmosphere for a few years after a major eruption, significant quantities are generally deposited over vast areas within days.

The samples they studied ranged from slightly more than 12 million years old to as young as 600,000 years old, a time span when volcanism was rampant in the western United States owing to the ongoing subduction of the Pacific plate under the continental crust of the North American plate.

“As we use these ashes that are present on either side of the mountain range, we can directly compare what the water looked like before and after it had to cross this barrier to atmospheric flow,” Mulch said. “If you just stay behind the mountain range, you see the effect of the rain shadow, but you have to make inferences about where the water vapor is coming from, what happened to the clouds before they traveled across the mountain range.

“For the first time, we were able to document that we can track the [development of the] rain shadow on both sides of the mountain range over very long time scales.”

Until now, researchers have been guided largely by “very good geophysical evidence” indicating that the range reached its present elevation approximately 3 or 4 million years ago, owing to major changes in the subsurface structure of the mountains, Mulch said.

“There was a very dense root of the Sierra Nevada, rock material that became so dense that it actually detached and sank down into the Earth’s mantle, just because of density differences,” Mulch said. “If you remove a very heavy weight at the base of something, the surface will rebound.”

The rebound of the range after losing such a massive amount of material should have been substantial. But, Mulch said, “We do not observe any change in the surface elevation of the Sierra Nevada at that time, and that’s what we were trying to test in this model.”

However, Mulch said he does not think his results refute the geophysical evidence. It could be that the Sierra Nevada did not evolve uniformly along its 400-mile length, he said. The geophysical data indicating the loss of the crustal root is from the southern Sierra Nevada; Mulch’s study focused more on the northern and central part of the range. In the southern Sierra Nevada, the weather patterns are different, and the rain shadow effect that Mulch’s approach hinges on is less pronounced.

“That’s why it’s important to have information that’s coming from deeper parts of the Earth’s crust and from the surface and try to correlate these two,” Mulch said. To really understand periods in the Earth’s past where climate conditions were markedly different from today, he said, “you need to have integrated studies.”

The research was funded by the National Science Foundation.

Earthquake Season in the Himalayan Front

Scientists have long searched for what triggers earthquakes, even suggesting that tides or weather play a role. Recent research spearheaded by Jean-Philippe Avouac, professor of geology and director of the Tectonics Observatory at the California Institute of Technology, shows that in the Himalayan mountains, at least, there is indeed an earthquake season. It’s winter.

For decades, geologists studying earthquakes in the Himalayan range of Nepal had noted that there were far more quakes in the winter than in the summer, but it was difficult to assign a cause. “The seasonal variation in seismicity had been noticed years ago,” says Avouac. Now, over a decade of data from GPS receivers and satellite measurements of land-water storage make it possible to connect the monsoon season with the frequency of earthquakes along the Himalaya front. The analysis also provides key insight into the timescale of earthquake nucleation in the region.

Avouac will present the results of the study on December 12 at the annual meeting of the American Geophysical Union (AGU) in San Francisco. They are also available online through the journal Earth and Planetary Science Letters, and will appear in print early next year.

The world’s tallest mountain range, the Himalaya continues to rise as plate tectonic activity drives India into Eurasia. The compression from this collision results in intense seismic activity along the front of the range. Stress builds continually along faults in the region, until it is released through earthquakes.

Avouac and two collaborators from France and Nepal–Laurent Bollinger and Sudhir Rajaure–began their earthquake seasonality investigation by analyzing a catalog of around 10,000 earthquakes in the Himalaya. They saw that, at all magnitudes above this detection limit, there were twice as many earthquakes during the winter months–December through February–as during the summer. That is, in winter there are up to 150 earthquakes of magnitude three per month, and in summer, around 75. For magnitude four, the winter average is 16 per month, while in summer the rate falls to eight per month. They ran the numbers through a statistical calculation and ruled out the possibility that the seasonal signal was due merely to chance.

“The signal in the seismicity is real; there is no discussion,” Avouac says. “We see this seasonal cycle,” he adds. “We didn’t know where it came from but it is really strong. We’re looking at something that is changing on a yearly basis-the timescale over which stress changes in this region is one year.”

Earlier studies suggested that seasonal variations in atmospheric pressure set off earthquakes, and this had been proposed for seasonal seismicity following the 1992 Landers, California, quake.

The scientists turned to satellite measurements of water levels in the region. Using altimetry data from TOPEX/Poseidon, a satellite launched in 1992 by NASA and the French space agency CNES (Centre National d’Etudes Spatiales), they evaluated the water level in major rivers of the Ganges basin to within a few tens of centimeters. They found that the water level over the whole basin begins its four-meter rise at the onset of the monsoon season in mid-May, reaching a maximum in September, followed by a slow decrease until the next monsoon season.

They combined river level measurements with data from NASA’s GRACE–Gravity Recovery and Climate Experiment–mission, which studies, among other things, groundwater storage on landmasses. The data revealed a strong signal of seasonal variation of water in the basin. Paired with the altimetry data, these measurements paint a complete picture of the hydrologic cycle in the region.

In the Himalaya, monsoon rains swell the rivers of the Ganges basin, increasing the pressure bearing down on the region. As the rains stop, the river water soaks through the ground and the built-up load eases outward, toward the front of the range. This outward redistribution of stress after the rains end leads to horizontal compression in the mountain range later in the year, triggering the wintertime earthquakes.

The final piece connecting winter earthquake frequency to season, and lending insight into the process by which earthquakes nucleate, lay in GPS data. Installation of GPS instruments across the Himalayan front began in 1994, and now they provide a decade’s worth of measurements showing land movement across the region. Instead of looking at vertical motions, which are widely believed to be sensitive to weather and the same forces that cause tides on Earth, the scientists concentrated on horizontal displacements. The lengthy records, analyzed by Pierre Bettinelli during his graduate work at Caltech, show that horizontal motion is continuous in the range front. Stress constantly builds in the region. But just as water levels near their lowest in the adjacent Ganges basin and earthquakes begin their doubletime, horizontal motion reaches its maximum speed.

“We had been staring at [the seasonal signal] for years, and then the satellite data came in and we deployed the GPS network and suddenly it became crystal clear,” says Avouac. “It’s like something you dream of.”

While many scientists have suggested that changing water levels can influence the earthquake cycle, a definitive mechanism had yet to be pinpointed. “There are two main avenues by which people have tried to understand the physics of earthquakes: Earth tides and aftershocks,” says Avouac. With the water level data, he could show that the rate at which stress builds along the rangefront, rather than the absolute level of stress, triggers earthquakes.

Although Earth tides induce stress levels similar to what builds up during seasonal water storage, they only vary over a 12-hour period. The Himalayan signal shows that it is more likely that earthquakes are triggered after stress builds for weeks to months, which matches the timescale of seasonal stress variation in that region.

About other earthquake-prone regions Avouac says, “seasonal variation has been reported in other places, but I don’t know any other place where it is so strong or where the cause of the signal is so obvious.”

Other authors on the paper are Pierre Bettinelli, Mireille Flouzat, and Laurent Bollinger of the Commissariat a l’Énergie Atomique, France; Guillaume Ramillien of the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, France; and Sudhir Rajaure and Som Sapkota of the National Seismological Centre in Nepal.

Avouac will present details of the group’s findings at AGU on Wednesday, December 12, at 2 p.m., Moscone West room 3018, in session T33F: Earthquake geology, active tectonics, and mountain building in south and east Asia.

Evolution Tied to Earth Movement

Kibo Summit of Kilimanjaro
Kibo Summit of Kilimanjaro

Scientists long have focused on how climate and vegetation allowed human ancestors to evolve in Africa. Now, University of Utah geologists are calling renewed attention to the idea that ground movements formed mountains and valleys, creating environments that favored the emergence of humanity.

“Tectonics [movement of Earth’s crust] was ultimately responsible for the evolution of humankind,” Royhan and Nahid Gani of the university’s Energy and Geoscience Institute write in the January, 2008, issue of Geotimes, published by the American Geological Institute.

They argue that the accelerated uplift of mountains and highlands stretching from Ethiopia to South Africa blocked much ocean moisture, converting lush tropical forests into an arid patchwork of woodlands and savannah grasslands that gradually favored human ancestors who came down from the trees and started walking on two feet – an energy-efficient way to search larger areas for food in an arid environment.

In their Geotimes article, the Ganis – a husband-and-wife research team who met in college in their native Bangladesh – describe this 3,700-mile-long stretch of highlands and mountains as “the Wall of Africa.” It parallels the famed East African Rift valley, where many fossils of human ancestors were found.

“Because of the crustal movement or tectonism in East Africa, the landscape drastically changed over the last 7 million years,” says Royhan Gani (pronounced rye-hawn Go-knee), a research assistant professor of civil and environmental engineering. “That landscape controlled climate on a local to regional scale. That climate change spurred human ancestors to evolve from apes.”

Hominins – the new scientific word for humans (Homo) and their ancestors (including Ardipithecus, Paranthropus and Australopithecus) – split from apes on the evolutionary tree roughly 7 million to 4 million years ago. Royhan Gani says the earliest undisputed hominin was Ardipithecus ramidus 4.4 million years ago. The earliest Homo arose 2.5 million years ago, and our species, Homo sapiens, almost 200,000 years ago.

Tectonics – movements of Earth’s crust, including its ever-shifting tectonic plates and the creation of mountains, valleys and ocean basins – has been discussed since at least 1983 as an influence on human evolution.

But Royhan Gani says much previous discussion of how climate affected human evolution involves global climate changes, such as those caused by cyclic changes in Earth’s orbit around the sun, and not local and regional climate changes caused by East Africa’s rising landscape.

A Force from within the Earth

The geological or tectonic forces shaping Africa begin deep in the Earth, where a “superplume” of hot and molten rock has swelled upward for at least the past 45 million years. This superplume and its branching smaller plumes help push apart the African and Arabian tectonic plates of Earth’s crust, forming the Red Sea, Gulf of Aden and the Great Rift Valley that stretches from Syria to southern Africa.

As part of this process, Africa is being split apart along the East African Rift, a valley bounded by elevated “shoulders” a few tens of miles wide and sitting atop “domes” a few hundreds of miles wide and caused by upward bulging of the plume.

The East African Rift runs about 3,700 miles from the Ethiopian Plateau south-southwest to South Africa’s Karoo Plateau. It is up to 370 miles wide and includes mountains reaching a maximum elevation of about 19,340 feet at Mount Kilimanjaro.

The rift “is characterized by volcanic peaks, plateaus, valleys and large basins and freshwater lakes,” including sites where many fossils of early humans and their ancestors have been found, says Nahid Gani (pronounced nah-heed go-knee), a research scientist. There was some uplift in East Africa as early as 40 million years ago, but “most of these topographic features developed between 7 million and 2 million years ago.”

A Wall Rises and New Species Evolve

“Although the Wall of Africa started to form around 30 million years ago, recent studies show most of the uplift occurred between 7 million and 2 million years ago, just about when hominins split off from African apes, developed bipedalism and evolved bigger brains,” the Ganis write.

“Nature built this wall, and then humans could evolve, walk tall and think big,” says Royhan Gani. “Is there any characteristic feature of the wall that drove human evolution?”

The answer, he believes, is the variable landscape and vegetation resulting from uplift of the Wall of Africa, which created “a topographic barrier to moisture, mostly from the Indian Ocean” and dried the climate. He says that contrary to those who cite global climate cycles, the climate changes in East Africa were local and resulted from the uplift of different parts of the wall at different times.

Royhan Gani says the change from forests to a patchwork of woodland and open savannah did not happen everywhere in East Africa at the same time, and the changes also happened in East Africa later than elsewhere in the world.

The Ganis studied the roughly 300-mile-by-300-mile Ethiopian Plateau – the most prominent part of the Wall of Africa. Previous research indicated the plateau reached its present average elevation of 8,200 feet 25 million years ago. The Ganis analyzed rates at which the Blue Nile River cut down into the Ethiopian Plateau, creating a canyon that rivals North America’s Grand Canyon. They released those findings in the September 2007 issue of GSA Today, published by the Geological Society of America.

The conclusion: There were periods of low-to-moderate incision and uplift between 29 million and 10 million years ago, and again between 10 million and 6 million years ago, but the most rapid uplift of the Ethiopian Plateau (by some 3,200 vertical feet) happened 6 million to 3 million years ago.

The Geotimes paper says other research has shown the Kenyan part of the wall rose mostly between 7 million and 2 million years ago, mountains in Tanganyika and Malawi were uplifted mainly between 5 million and 2 million years ago, and the wall’s southernmost end gained most of its elevation during the past 5 million years.

“Clearly, the Wall of Africa grew to be a prominent elevated feature over the last 7 million years, thereby playing a prominent role in East African aridification by wringing moisture out of monsoonal air moving across the region,” the Ganis write.

That period coincides with evolution of human ancestors in the area.

Royhan Gani says the earliest undisputed evidence of true bipedalism (as opposed to knuckle-dragging by apes) is 4.1 million years ago in Australopithecus anamensis, but some believe the trait existed as early as 6 million to 7 million years ago.

The Ganis speculate that the shaping of varied landscapes by tectonic forces – lake basins, valleys, mountains, grasslands, woodlands – “could also be responsible, at a later stage, for hominins developing a bigger brain as a way to cope with these extremely variable and changing landscapes” in which they had to find food and survive predators.

For now, Royhan Gani acknowledges the lack of more precise timeframes makes it difficult to link specific tectonic events to the development of upright walking, bigger brains and other key steps in human evolution.

“But it all happened within the right time period,” he says. “Now we need to nail it down.”