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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Katrina
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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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