Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

With supercooling and the right geometry, ’warm’ glaciers can trap and transport silt

15.08.2003


It may take them a century to advance a few meters, but the bottoms of some glaciers churn with supercooled activity, according to an article by a Lehigh University geologist in the Aug. 14 issue of Nature magazine.



Edward B. Evenson, professor of earth and environmental sciences, says his team’s 12-year study of the Matanuska Glacier in south-central Alaska sheds light on a riddle that has long baffled geologists - how glaciers are able to pick up and transport silt.

The findings of Evenson and his colleagues may also help geologists better understand the Laurentide Ice Sheet glaciers that covered Canada and much of the northern United States during the most recent Ice Age.


The Nature article, titled "Stabilizing feedbacks in glacier-bed erosion," explains how glaciers "often erode, transport and deposit sediment much more rapidly than nonglacial environments." Evenson and his students and colleagues have published 20 articles related to that topic since 1996.

When air temperatures rise and cause the ice on a glacier’s surface to melt, Evenson and his group found, water penetrates through the glacier until it reaches the bottom. There, under massive pressure from the weight of the glacier above, the water becomes supercooled and its freezing point drops by a fraction of a degree, As the water flows up and out from under the glacier however, the pressure is reduced and some of the supercooled water re-freezes to form what geologists call "frazil ice" - minute crystals of ice that float atop the remaining water.

As the pressure from above continues to lessen, the frazil ice becomes larger and begins to attach to the bottom of the glacier. There, it picks up particles of silt from the dirty, silt-laden water flowing beneath the glacier, much the same as an air filter in a car removes dust and dirt from the air. As the glacier flows, grains of silt are trapped in the interstitial spaces of the ice crystals. The sediment and ice eventually separate from each other, producing layers of clean and dirty ice. This process goes on all summer as melting water penetrates down to the glacier bed.

Evenson’s analysis of the "basal-stratified ice" beneath the Matanuska Glacier also found traces of tritium, an isotope of hydrogen that has been released into the atmosphere during the past 50 years by nuclear weapons testing.

"The tritium tells us that this basal-stratified ice is young," says Evenson. By contrast, he says, the ice on top of the glacier, which is not nearly so dynamic, is estimated to be several hundred years old.

The supercooling process does not occur in the "cold" glaciers of Antarctica and Greenland, where mean annual temperatures remain below freezing and prevent melting water from penetrating to the bottom of the ice sheet, says Evenson.

Among the world’s "warm" glaciers, which are found in Canada, Alaska, Iceland and many mountain ranges, the supercooling process is likely to occur only in those glaciers with what Evenson calls a favorable geometry.

Glaciers located in flat areas, like the Matanuska, says Evenson, are more likely than most mountain glaciers, including those in the Alps or the Cascades, to permit the supercooling necessary for basal-stratified ice to form. As a flatland glacier advances into a basin, the glacier’s shape changes, imposing the necessary pressure on the water that has penetrated to the glacier bottom.

"Because most mountain glaciers are moving downhill, the angle between the slope of the glacier’s surface and the slope of its base is not right. You need a relatively flat glacier and a subglacial basin, or ’overdeepening,’ and then supercooling occurs," Evenson says.

Evenson worked with researchers from the University of Buffalo, Pennsylvania State University, Michigan State University and the Cold Regions Research and Engineering Laboratory (CRREL) of Hanover, N.H., which helped fund the study. The researchers also received support from the National Science Foundation.

After studying the Matanuska Glacier, Evenson and his colleagues tried to determine if basal-stratified ice was forming in a similar manner at other warm glaciers. At the Malaspina Glacier in Alaska, they found vents full of frazil ice, indicating that the same process was occurring. In the glaciers of Iceland, they found supercooled water in over-deepened glaciers. They have concluded that this supercooling process occurs on all warm glaciers where the geometry is right, and that this same process most likely governed Ice Age glaciers. The Laurentide Ice Sheet, says Evenson, was warm along its margins and cold in its interior. As it retreated north between 18,000 and 10,000 years ago, the glacier left behind deposits of thick till, drumlins and eskers - demonstrating that it was warm at its margin.

Evenson and his students drilled hundreds of holes in glaciers, using a hose that sends boiling water through a glacier at a rate of about 1 meter per minute. By injecting a fluorescent dye and monitoring the vents through which the water comes out, the researchers were able to determine the shape and routing of the subglacial plumbing system.

Gregory Baker, a Lehigh-trained geophysicist now with the University of Buffalo, used a ground-penetrating laser to look through the glacier and measure its thickness and the amount of debris underneath it.


###
Besides Evenson and Baker, the Nature paper was co-authored by Richard B. Alley (Penn State), Daniel E. Lawson (CRREL), and Grahame Larson (Michigan State).

Kurt Pfitzer | EurekAlert!
Further information:
http://www.lehigh.edu/

More articles from Earth Sciences:

nachricht Early organic carbon got deep burial in mantle
25.04.2017 | Rice University

nachricht New atlas provides highest-resolution imagery of the Polar Regions seafloor
25.04.2017 | British Antarctic Survey

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

NASA's Fermi catches gamma-ray flashes from tropical storms

25.04.2017 | Physics and Astronomy

Researchers invent process to make sustainable rubber, plastics

25.04.2017 | Materials Sciences

Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017

25.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>