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Effects of Glaciation

               EFFECTS OF GLACIATION



Although the last glacial period ended more than 8,000 years ago, its effects can still be felt today.  For example, the moving ice carved out the landscape in Canada, Greenland, northern Eurasia and Antarctica.  The erratic boulders, till, drumlins, eskers, fjords, kettle lakes, moraines, cirques, horns, etc.., are typical features left behind by the glaciers.

 


 

 

  • Tills -  unstratified glacial drift consisting of clay, sand, gravel, and boulders intermingled
  • Drumlins - an elongate or oval hill of glacial drift
  • Eskers - a long narrow ridge or mound of sand, gravel, and boulders deposited by a stream flowing on, within, or beneath a stagnant glacier
  • Fjords - a narrow inlet of the sea between cliffs or steep slopes
  • Kettle Lakes - of outwash atop the irregular glacier terminus. Kettles may range in size from 5 m (15 feet) to 13 km (8 miles) in diameter and up to 45 m in depth. When filled with water they are called kettle lakes. Most kettles are circular in shape because melting blocks of ice tend to become rounded; distorted or branching depressions may result from extremely irregular ice masses.
  • Moraines - accumulation of rock debris (till) carried or deposited by a glacier. The material, which ranges in size from blocks or boulders (usually faceted or striated) to sand and clay, is unstratified when dropped by the glacier and shows no sorting or bedding. Several kinds of moraines are recognized:
  • Cirques - a deep steep-walled basin on a mountain usually forming the blunt end of a valley

·         Horns - flanks. Headward erosion of these cirques finally leaves only a sharp peak flanked by nearly vertical headwall cliffs, which are separated by arêtes. Such glacially eroded mountains are termed horns, the most widely known of which is the Matterhorn in the Swiss Alps.

The weight of the ice sheets was so great that they deformed the Earth’s crust and mantle.  After the ice sheets melted, the ice-covered land rebounded.  Due to the high viscosity of the Earth, the flow of mantle rocks which controls the rebound process is very slow – at a rate of about 1 cm/year near the center of rebound today.

 

During glaciation, water was taken from the oceans to form the ice at high latitudes, thus global sea level dropped by about 120 meters, exposing the continental shelves and forming land- bridges between land-masses for animals to migrate.  During deglaciation, the melted ice-water returned to the oceans, causing sea level to rise.  This process can cause sudden shifts in coastlines and hydration systems resulting in newly submerged lands, emerging lands, collapsed ice dams resulting in salination of lakes, new ice dams creating vast areas of freshwater, and a general alteration in regional weather patterns on a large but temporary scale.  It can even cause temporary reglaciation.  This type of chaotic pattern of rapidly changing land, ice saltwater and freshwater has been proposed as the likely model for the Baltic and Scandinavian regions, as well as much of central North America at the end of the last glacial maximum, with the present-day coastlines only being achieved in the last few millennia of prehistory.  Also, the effect of elevation on Scandinavia submerged a vast continental plain that had existed under much of what is now the North Sea, connecting the British Isles to continental Europe.

 

The redistribution of ice-water on the surface of the Earth and the flow of mantle rocks causes changes in the gravitational field as well as changes to the distribution of the moment of inertia of the Earth.  These changes to the moment of inertia result in a change in the angular velocity, axis, and wobble of the Earth’s rotation (Post-glacial rebound).  The weight of the redistributed surface mass loaded the lithosphere, caused it to flexure and also induced stress within the Earth.  The presence of the glaciers generally suppressed the movement of faults below (Johnston 1989, Wu & Hasegawa 1996, Turpeinen et al. 2008).  However, during deglaciation, the faults experience accelerated slip, and earthquakes are triggered (Post-glacial rebound).  Earthquakes triggered near the ice margin may in turn accelerate ice calving and may account for the Heinrich events (Hunt & Malin 1998).  As more ice is removed near the ice margin, more intraplate earthquakes are induced and this positive feedback may explain the fast collapse of ice sheets.   

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