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 Monitoring lava lake levels in Congo volcano
16.05.2018 | Seismological Society of America

nachricht Ice stream draining Greenland Ice Sheet sensitive to changes over past 45,000 years
14.05.2018 | Oregon State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Explanation for puzzling quantum oscillations has been found

So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics

Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...

Im Focus: Dozens of binaries from Milky Way's globular clusters could be detectable by LISA

Next-generation gravitational wave detector in space will complement LIGO on Earth

The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...

Im Focus: Entangled atoms shine in unison

A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.

The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...

Im Focus: Computer-Designed Customized Regenerative Heart Valves

Cardiovascular tissue engineering aims to treat heart disease with prostheses that grow and regenerate. Now, researchers from the University of Zurich, the Technical University Eindhoven and the Charité Berlin have successfully implanted regenerative heart valves, designed with the aid of computer simulations, into sheep for the first time.

Producing living tissue or organs based on human cells is one of the main research fields in regenerative medicine. Tissue engineering, which involves growing...

Im Focus: Light-induced superconductivity under high pressure

A team of scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg investigated optically-induced superconductivity in the alkali-doped fulleride K3C60under high external pressures. This study allowed, on one hand, to uniquely assess the nature of the transient state as a superconducting phase. In addition, it unveiled the possibility to induce superconductivity in K3C60 at temperatures far above the -170 degrees Celsius hypothesized previously, and rather all the way to room temperature. The paper by Cantaluppi et al has been published in Nature Physics.

Unlike ordinary metals, superconductors have the unique capability of transporting electrical currents without any loss. Nowadays, their technological...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Save the date: Forum European Neuroscience – 07-11 July 2018 in Berlin, Germany

02.05.2018 | Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

 
Latest News

Supersonic waves may help electronics beat the heat

18.05.2018 | Power and Electrical Engineering

Keeping a Close Eye on Ice Loss

18.05.2018 | Information Technology

CrowdWater: An App for Flood Research

18.05.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>