Glacial motion
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Himalaya
. Glacial lakes have been rapidly forming on the surface of the debris-covered glaciers in this region during the last few decades. USGS researchers have found a strong correlation between increasing temperatures and glacial retreat in this region.Glacial motion is the motion of
Jakobshavn Isbræ in Greenland)[1] or slow (0.5 metres per year (20 in/year) on small glaciers or in the center of ice sheets), but is typically around 25 centimetres per day (9.8 in/d).[2]
Processes of motion
Glacier motion occurs from four processes, all driven by gravity:
deformation
, and internal deformation.
- In the case of basal sliding, the entire glacier slides over its bed. This type of motion is enhanced if the bed is soft sediment, if the glacier bed is thawed and if meltwater is prevalent.
- Bed deformation is thus usually limited to areas of sliding. Seasonal melt ponding and penetrating under glaciers shows seasonal acceleration and deceleration of ice flows affecting whole icesheets.[3]
- Some glaciers experience glacial quakes—glaciers "as large as Manhattan and as tall as the Empire State Building, can move 10 meters in less than a minute, a jolt that is sufficient to generate moderate seismic waves."[4] There has been an increasing pattern of these ice quakes - "Quakes ranged from six to 15 per year from 1993 to 2002, then jumped to 20 in 2003, 23 in 2004, and 32 in the first 10 months of 2005."[5]A glacier that is frozen up to its bed does not experience basal sliding.
- Internal deformation occurs when the weight of the ice causes the deformation of ice crystals. This takes place most readily near the glacier bed, where pressures are highest. There are glaciers that primarily move via sliding, glacial quakes, and others that move almost entirely through deformation.
Terminus movement and mass balance
If a glacier's terminus moves forward faster than it melts, the net result is advance. Glacier retreat occurs when more material ablates from the terminus than is replenished by flow into that region.
Glaciologists consider that trends in
global warming.[6]
As a glacier thins, due to the loss of mass it will slow down and crevassing will decrease.
Landscape and geology
Studying glacial motion and the landforms that result requires tools from many different disciplines: physical geography, climatology, and geology are among the areas sometime grouped together and called earth science.
During the
depositional landforms were created, such as moraines, eskers, drumlins, and kames. The stone walls found in New England (northeastern United States) contain many glacial erratics
, rocks that were dragged by a glacier many miles from their bedrock origin.
At some point, if an
glacial till
.
See also
References
- ^ "Table of fastest glacier speeds at". Antarcticglaciers.org. Retrieved 2018-08-16.
- ^ "Glacier properties Hunter College CUNY lectures". Archived from the original on 2014-02-22. Retrieved 2014-02-06.
- ^ Surface Melt-Induced Acceleration of Greenland Ice-Sheet Flow Originally published in Science Express on 6 June 2002, Science 12 July 2002: Vol. 297. no. 5579, pp. 218 - 222.
- ^ Harvard News Office (2006-04-06). "Global warming yields 'glacial earthquakes' in polar areas". News.harvard.edu. Archived from the original on 2013-09-27. Retrieved 2013-09-24.
- ^ Glacial earthquakes rock Greenland ice sheet 12:36 24 March 2006, NewScientist.com news service
- ^ "Climate Change 2001: The Scientific Basis". Grida.no. Archived from the original on 2014-09-01. Retrieved 2013-09-24.
External links
- How glaciers form and flow
- Trends in glacier mass balance Archived 2012-01-02 at the Wayback Machine
- Animation of glacial advance
- Advance and retreat of Columbia Glacier in Prince William Sound
- Physical geography of glacial landforms
- Links to more glacier resources online Archived 2005-03-08 at the Wayback Machine