Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Glacial Erosion Changes Mountain Responses to Plate Tectonics

18.11.2008
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."

* The article, Quaternary tectonic response to intensified glacial erosion in an orogenic wedge, was written by Berger, a Virginia Tech geosciences Ph.D. graduate, now a geoscientist with ConocoPhillips; Gulick; Spotila; Phaedra Upton, post-doctoral fellow at the University of Maine, now a research fellow at the University of Otago; John M. Jaeger, associate professor of geology, University of Florida; James B. Chapman of the University of Texas, El Paso; Lindsay A. Worthington, a graduate student at the University of Texas at Austin; Pavlis; Kenneth D. Ridgway, professor of earth and atmospheric sciences at Purdue University; Bryce A. Willems, Ph.D. candidate in the geological and environmental geosciences at Northern Illinois University; and Ryan J. McAleer, a Virginia Tech geosciences M.S graduate, now a geoscientist with the U.S. Geological Survey. Published online: October 26, 2008 (http://www.nature.com/ngeo/journal/v1/n11/abs/ngeo334.html).

The research by Berger and Spotila is also the cover story in the July 2008 issue of Geology: http://geology.geoscienceworld.org/cgi/content/abstract/36/7/523

(Subscribers to Nature Geoscience can read the dramatic "Backstory" in the October issue of the journal, which talks about the researchers jumping out of a helicopter in snow and fog and about bears apparently gleefully destroying equipment. Nonsubscribers can find a description of the adventures of collecting data in these environs in a 2004 article in Science Daily at http://www.sciencedaily.com/releases/2004/05/040526070308.htm )

Drs. Berger and Spotila are the corresponding authors. Reach Spotila at spotila@vt.edu and Berger at alberger@vt.edu.

Learn more about Spotila's research here: http://www.geos.vt.edu/people/spotila/
Learn more about Berger's research while at Virginia Tech here: http://filebox.vt.edu/users/alberger/index.htm

Learn about STEEP here: http://www.ig.utexas.edu/steep/

Susan Trulove | Newswise Science News
Further information:
http://www.vt.edu

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

Gold shines through properties of nano biosensors

17.08.2017 | Physics and Astronomy

Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter

17.08.2017 | Earth Sciences

Mars 2020 mission to use smart methods to seek signs of past life

17.08.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>