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Ice on the Land

Glaciation Periods:  colder periods which last for millions of years. Large masses of ice cover parts of the Earth's surface. The last one began around 2.6 million years ago. Glacial periods are the cooler periods of the ice age when the ice advancaes to cover more of the Earth's surface. 

Interglacial Periods: warmer periods inbetween glacial periods where the ice retreats to cover less of the Earth's surface. 

Glacier: masses of ice that fill valleys and hollows. They move downhill under the force of gravity.

Zone of accumulation: accumulation is the input of snow and ice into the glacier. Therefore, there is more accumulation at the top of the glacier than at the bottom, this is called the zone of accumulation. 

Zone of ablation: ablation is the output of water from a glacier as ice melts. In the lower part of the glacier, there is more ablation than accumulation - this is therefore called the zone of ablation. 

Glacial Budget: the difference between total accumulation and total ablation in one year.

> During winter, there is a positive glacial budget, in which there is more accumulation than there is ablation. 

During a positive glacial budget, the glacier gets larger and the snout (bottom end of the glacier) advances down the valley (THINK: more snow = bigger/longer glacier)

> During summer, there is a negative glacial budget, in which there is more ablation than there is accumulation.

During a negative glacial budget, the glacier gets smaller and the snout retreats up the valley. (THINK: less snow = smaller/shorter glacier) 

> If there's the same amount of accumulation as there is ablation in one year, the glacier stays the same size and position of the snout doesn't change. 

> Since 1950, most of the glaciers have had a negative glacial budget due to global warming, so the glaciers have been retreating. 

Rhone Glacier, Switzerland

Rhone Glacier is a case study of a retreating glacier. It is placed upon the Swiss-Alps and is currently around 7.8km long. It has been retreating, likewise with most glaciers, since the 19th century. The meltwater from zone of ablation has formed a new lake infront of the glacier which is increasing in size, showing the glacier has been melting more rapidly. This is said to be from global warming - with an average temperature increase of 1.8 degrees around Rhone. 

Glacial Erosion

Plucking: occurs when meltwater at the base, back or sides of a glacier freezes onto the rock. As the glacier moves forward, it pulls bits of rock out.

Abrasion: when bits of rock stuck in the ice grind against the rock below the glacier, wearing it away (the sandpaper technique - as though the rock in the ice acts as sandpaper against the rock below the glacier)

Rotational Slip: the circular motion at which ice at the top of the glacier moves

Freeze-thaw weathering: where water gets into cracks in rocks.


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