Glacial motion


Glacial motion

Glacial motion is the motion of glaciers, which can be likened to rivers of ice. It has played an important role in sculpting many landscapes. Most lakes in the world occupy basins scoured out by glaciers. Glacial motion can be fast (up to 30 m/day, observed on Jakobshavns Isbrae in Greenland) or slow (0.5 m/year on small glaciers or in the center of ice sheets).

Glacier motion occurs from three processes, all driven by gravity: basal sliding, glacial quakes generating fractional movements of large sections of ice, 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. Seasonal melt ponded and penetrating under glaciers shows seasonal acceleration and deceleration of ice flows affecting whole icesheets. [ [http://www.sciencemag.org/cgi/content/abstract/297/5579/218 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.] 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." [ [http://www.news.harvard.edu/gazette/2006/04.06/05-ekstrom.html Global warming yields 'glacial earthquakes' in polar areas] ] 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." [ [http://environment.newscientist.com/article/dn8889.html Glacial earthquakes rock Greenland ice sheet] 12:36 24 March 2006, NewScientist.com news service] 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.

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 mass balance for glaciers are more fundamental than the advance or retreat of the termini of individual glaciers. In the years since 1960, there has been a striking decline in the overall volume of glaciers worldwide. This decline is correlated with global warming. [http://www.grida.no/climate/ipcc_tar/wg1/064.htm] As a glacier thins, due to the loss of mass it will slow down and crevassing will decrease.

At some point, if an Alpine glacier becomes too thin it will stop moving. This will result in the end of any basal erosion. The stream issuing from the glacier will then become clearer as glacial flour diminishes.

During the Pleistocene (the last ice age), huge sheets of ice called continental glaciers advanced over much of the earth. The movement of these continental glaciers created many now-familiar glacial landforms. As the glaciers were expanded, due to their accumulating weight of snow and ice, they crushed and redistributed surface rocks, creating erosional landforms such as s, cirques, and hanging valleys.

Later, when the glaciers retreated leaving behind their freight of crushed rock and sand, 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.

Lakes and ponds can also be caused by glacial movement. Kettle lakes form when a retreating glacier leaves behind an underground chunk of ice. Moraine-dammed lakes occur when a stream (or snow runoff) is dammed by glacial till.

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.

ee also

* Cryoseism
* Glacial lake outburst flood

External links

* [http://www.geography-site.co.uk/pages/physical/glaciers/origin.html How glaciers form and flow]
* [http://nsidc.org/sotc/glacier_balance.html Trends in glacier mass balance]
* [http://www.wwnorton.com/earth/egeo/animations/ch18.htm Animation of glacial advance]
* [http://www.wwnorton.com/earth/egeo/features/ch18_2.htm Advance and retreat of Columbia Glacier in Prince William Sound]
* [http://www.physicalgeography.net/fundamentals/10af.html Physical geography of glacial landforms]
* [http://www.cln.org/themes/glaciers.html Links to more glacier resources online]
* [http://www.nichols.edu/departments/glacier.html North Cascade Glacier Climate Project Research]

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • glacial landform — ▪ geology Introduction  any product of flowing ice and meltwater. Such landforms are being produced today in glaciated areas, such as Greenland, Antarctica, and many of the world s higher mountain ranges. In addition, large expansions of present… …   Universalium

  • Glacial landform — Antique postcard shows rocks scarred by glacial erosion. Yosemite Valley …   Wikipedia

  • motion — Synonyms and related words: Zeitgeist, act, action, activeness, activism, activity, agitation, bearing, beck, beckon, bill, body language, business, calendar, carriage, change, charade, chironomy, clause, clockworks, commotion, commutation,… …   Moby Thesaurus

  • Post-glacial rebound — A model of present day mass change due to post glacial rebound and the reloading of the ocean basins with seawater. Blue and purple areas indicate rising due to the removal of the ice sheets. Yellow and red areas indicate falling as mantle… …   Wikipedia

  • Glacier — This article is about the geological formation. For other uses, see Glacier (disambiguation). The Baltoro Glacier in the Karakoram, Kashmir, Northern Pakistan. At 62 kilometres (39 mi) in length, it is one of the longest alpine glaciers on… …   Wikipedia

  • Ice sheet dynamics — describe the motion within large bodies of ice, such those currently on Greenland and Antarctica. Ice motion is dominated by the movement of glaciers, whose gravity driven activity is controlled by two main variable factors: the temperature and… …   Wikipedia

  • Physical geography — For other uses, see Physiographic regions of the world. True color image of the Earth s surface and atmosphere. NASA Goddard Space Flight Center image. Physical geography (also known as geosystems or physiography) is one of the two major… …   Wikipedia

  • East River — The East River is a tidal strait in New York City. It connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates Long Island (including the boroughs of Queens and Brooklyn) from the island of Manhattan and… …   Wikipedia

  • Thomas Chrowder Chamberlin — Infobox Scientist name = PAGENAME box width = image size =150px caption = PAGENAME birth date = September 25,1843 birth place = Mattoon, Illinois death date = November 15, 1928 death place = Chicago residence = citizenship = nationality =… …   Wikipedia

  • Moulin (geology) — Schematic drawing of glacial features illustrating how moulins transport surface water to the base of the glacier …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.