Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Satellites see shadows of ancient glaciers

14.05.2004


People in the central and eastern United States and Canada are used to the idea that the land they live on -- its variety of hills, lakes and rivers -- are left over from the great mile-thick ice sheets that covered the area 18,000 years ago.



They may, however, be surprised to learn that today, long after the glaciers melted, an international research team led by Northwestern University geologists using the Global Positioning System (GPS) satellites can "see" the land moving -- up to half an inch per year in some places -- as the earth rebounds in response to the ice that once pushed the land down.

Looking at data from more than 200 sites across the continent, the researchers discovered a spectacular pattern. While sites in Canada are rising, with those near Hudson Bay (where the ice load was heaviest) rising the fastest, U.S. sites south of the Great Lakes are sinking instead of rebounding.


Giovanni Sella, postdoctoral fellow in the department of geological sciences at Northwestern, will present the research team’s results at 2 p.m. Wednesday, May 19, at the Spring Joint Assembly of the American Geophysical Union and Canadian Geophysical Union in Montreal, Canada.

"If you take the load off of road tar it won’t pop back immediately," said Seth Stein, professor of geological sciences at Northwestern. "The earth is similar -- the ground continues to rebound as the viscous mantle flows back in. It is amazing that we can actually see this going on now. The glaciers continue to make their presence felt."

These small motions resulting from "post-glacial rebound" (GPS can detect motions as small as 1/25 of an inch per year) stem from the fact that the mantle below the earth’s crust flows like a super-viscous fluid -- much, much stickier than road tar or maple syrup. The mantle is still flowing to fill areas underneath the places where the heavy ice sheets pushed out the mantle 18,000 years ago.

Post-glacial rebound also affects the water levels of the Great Lakes. As the northern shores rise, water levels are steadily decreasing. Conversely, as the southern shores sink, water levels are rising. This impacts not only industries and homeowners along the shores of the Great Lakes but also the international management of water levels, dams and shipping.

These small motions may well be one of the causes of the mysterious earthquakes that occur in the center of the North American continent, including the St. Lawrence Valley, northern New England, and perhaps even the New Madrid earthquake zone in the central United States, and along the Atlantic coast including Newfoundland.

"This idea has been around for a while, but until now, no one knew how large the ground movements were across the area," said Stein. "We believe they may have significant effects."

Another good reason to study post-glacial rebound is that it tells about the properties of the deeper earth. The initial GPS results indicate that the lower mantle (below a depth of 400 miles) is probably not much stiffer than the upper mantle, contrary to what has been often thought.

In addition to Sella and Stein, other members of the project include Timothy Dixon and Shimon Wdowinski from the University of Miami; Michael Craymer from the Geodetic Survey Division of Natural Resources Canada; Thomas James and Stephane Mazzotti from the Geological Survey of Canada of Natural Resources Canada; and Roy Dokka from Louisiana State University.

Megan Fellman | EurekAlert!
Further information:
http://www.northwestern.edu/news/

More articles from Earth Sciences:

nachricht Research sheds new light on forces that threaten sensitive coastlines
24.04.2017 | Indiana University

nachricht NASA sees the end of ex-Tropical Cyclone 02W
21.04.2017 | NASA/Goddard Space Flight Center

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

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

Two-dimensional melting of hard spheres experimentally unravelled after 60 years

24.04.2017 | Life Sciences

Molecular libraries for organic light-emitting diodes

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>