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 Six-decade-old space mystery solved with shoebox-sized satellite called a CubeSat
15.12.2017 | National Science Foundation

nachricht NSF-funded researchers find that ice sheet is dynamic and has repeatedly grown and shrunk
15.12.2017 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>