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Moving Mountains

Photo courtesy of Peter Koons


Moving Mountains
Geodynamicist Peter Koons studies the activity of world's highest peaks to model the evolution of the Earth

About the Photo: In Namche Barwa in eastern Tibet, the Tsangpo River gorge is one of the deepest and steepest on Earth. This erosional incision focuses tectonic deformation into the region, forming a "tectonic aneurysm." The west face of Namche Barwa rises almost vertically from a glacial moraine that once blocked the Tsangpo.
 

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Geophysicist Laura Serpa and geoscientist Terry Pavlis have spent their professional careers studying how forces of nature have sculpted the Earth over millions of years.
 

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Maine native Peter Koons has long harbored a fascination with the intrinsic beauty and mystery of high mountains. It's when he started asking why the world's high mountains occurred that the summits captured his scientific attention and he saw them for what they are anything but static.

"A lot of influence came from the New Zealand mountains that are exceptionally active. They go up quickly and come down quickly," says Koons, who today is one of the world leaders in understanding the interactions among tectonics, surface evolution and climate change. "It's there that I first formed an image in my mind of how quickly plate tectonics work and how quickly the earth is behaving."

Koons was 17 when he left Maine to study in New Hampshire, New Zealand and Switzerland. He was climbing mountains in the western United States and Canada, but it wasn't until he went abroad and lived for 26 years that he came to understand the dynamics of the world's mountains.

His research has taken him to the most active mountain-building regions of the world. In New Zealand's Southern Alps, where earthquakes and 12 meters of rain a year can bring down huge chunks of earth, the size and shape of mountains can change year after year. Similarly in the western and eastern Himalayas of Pakistan and Tibet, landslides and earthquakes quickly move earth that causes a chain of events that alter the landscape. He also has focused on Norwegian Caledonides and Alaska's Mt. St. Elias range, where tectonics and surface processes are extremely active.

"Mountains are vertical perturbations to both earth and atmosphere, and as such are remarkably sensitive to the behavior of both, providing the most vigorous links between earth and air," says Koons, an associate professor of Earth sciences at the University of Maine. "The shapes protrude into the atmosphere, changing local climate."

The key is in knowing how plate tectonics affects climate, and how climate affects the evolution of mountains at tectonic plate boundaries.
 

Koons is a geodynamicist who uses continuum mechanics to understand the powerful links between the Earth and the atmosphere. He compares data sets from natural mountain belts with mathematical or numerical three-dimensional computer models to hypothesize about mechanisms and rates of geologic processes. His goal is to characterize the evolution of the Earth's lithosphere or crust to understand the causes and effects of changes in the landscape, and then to forecast how the Earth will respond to future changes.

In particular, Koons seeks to understand the forces of nature such as deglaciation and erosion that put significant strain and stress on the Earth surface, resulting in changes above and below ground. Modeling how the Earth responded in the past could allow us to predict future strains and the landscape-altering events. But the challenges are many. Historical datasets often are incomplete, which is why the modeling Koons has developed has the ability to glean information from other disciplines, such as climatology and archaeology. In addition, geological data tends to stretch out over long time frames of millions of years; Koons wants to reduce those time frames in order to make more relevant forecasts.

"We can use the information we have within the reference frame to make forecasts," Koons says. "We will not be predicting earthquakes and hurricanes, but forecasting the general probability of various events. I'd like to see it involved in policymaking."

Other challenges in geophysics are found in the paradoxes or the counter-intuitive realities of how plate tectonics and climate change interface. For instance, it seems logical that high mountains, which intercept more moisture, would be sites of the highest erosion rates. But numerical modeling demonstrates that assumption to be flawed in the most active mountains, where elevations are reduced where erosion rates are highest. These high erosion rates, in turn, focus deformation, which, in turn, affects the incidence of earthquakes.

At corners or syntaxes where tectonic plates meet, as in Nanga Parbat in the northwest Himalayan range and St. Elias in Alaska, unusually fast exhumation (uplift and erosion) leads to very high mountains and rocks exposed at the surface that less than a million years ago were buried many kilometers deep in the Earth at temperatures up to 700 degrees C. When rivers carry soil and rock downstream, the Earth's crust thins, reducing pressure on the underlying rock layers and allowing them move to those low-pressure zones of mountainous regions. Koons and his Himalayan colleague Peter Zeitler characterize the phenomenon as a "tectonic aneurysm."

"Vertical perturbations caused by erosion and exhumation alter the thermal and, therefore, the strength profiles of the Earth," Koons says. "This thermal/deformation feedback causes the greatest mountain elevations to form adjacent to areas where erosion is most vigorous."
 

The modeling Koons does encourages geoscientists like Terry Pavlis of the University of New Orleans to "think differently" about the changes occurring in the world's high, active mountains. For Pavlis, the principal investigator on the five-year, $4.5 million St. Elias Erosion/Tectonics Project (STEEP), modeling has helped characterize the dynamics of plate boundary processes, including huge, rapid geological changes taking place on time scales of half a million years or less.

As a member of the NSF team studying St. Elias, Koons is developing a comprehensive model to explain the evolution of the Gulf of Alaska, including the origins of mountains and the interaction of crustal processes, such as the redistribution of mass by glacial and stream transport. The results will have implications for understanding global mountain building processes at continental margins and the influence of those processes on climate.

Pavlis says Koons' modeling is the glue making the multidisciplinary STEEP a coherent research effort. Designed as a study of the evolution of the highest coastal mountain range on Earth, STEEP is a 10-institute collaborative involving the Universities of Alaska, Texas, Utah, New Orleans, Maine and Washington; Lehigh, Virginia Tech, Purdue and Indiana universities.

"Making predictions with models that can then be tested with continued field work is a huge step," says Pavlis, who is doing research in the UMaine Numerical Modeling Facility after the temporary closing of the University of New Orleans because of Hurricane Katrina. "With STEEP, we're partly there all ready. Now having Peter and me sitting at the same computer as we do the modeling will only accelerate the process."
 

The modeling takes into account a complex system of forces that, when acting together, reach thresholds that bring about qualitative change. Phenomena like dramatic continental deglaciation sets several forces in motion, crossing a threshold that has a massive effect not only on the Earth but also on subsequent society. In recent years, discoveries of evidence of rapid and often big shifts in climate by UMaine scientists Paul Mayewski, George Denton and others have given Koons more and more information to condition his models.

"I would not be doing this project if I didn't know those shifts occurred on what appears to be the static Earth," Koons says. "In addition, we're looking at information from archaeology and other areas to learn about societal behavior that occurred in response to deglaciation and sea level changes."

In the next five years, Koons and UMaine colleagues hope to develop an Earth Reference Model that describes the evolution of the Northern Hemisphere how climate and tectonics have shaped the Earth in the past 20,000 years, since the last Ice Age. To do that, he will compile datasets that, taken together like puzzle pieces, will flesh out how climate change and tectonics external and internal processes interacted since deglaciation. Knowing that evolution or response to changing conditions, short-term forecasts for the next 1,000 years could then be possible.

"To me, the Northern Hemisphere is most interesting because of the effect of the concentrated continental land masses. Here we can look at the changing terrestrial boundaries and the response of ecosystems to the removal of ice.

"What we're doing is describing the Earth's response to changing glacial cover, sea level change and weathering of the surface as a reflection of what's happening below the surface," he says.

Today, the behavior of Greenland's retreating ice cover provides a modern-day window into the early stages of deglaciation in Maine. With his colleagues, Koons hopes that the high mountains of Greenland will soon be the next focus of his research.

by Margaret Nagle
November-December, 2005

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