definitions for geography topics AS

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  • Created by: Ikra Amin
  • Created on: 30-04-14 20:12

Cold environments 1

PLUCKING - a process of glacial erosion by which a glacier freezes around a rock on a valley, and subsequent movement of the ice causes the rock to be pulled away with it. 

E.G. Roche Moutonnee (has a smooth side & rough side. - rough side is due to plucking as glacier travelled over the resistant rock)

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Calving - The process of ablation by which small masses of

ice break from an ice sheet or glacial. This can produce

icebergs if the edge of the ice sheet extends into the sea. 

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Sublimation - Involves a direct change of state from solid to

a gas without becoming a liquid.

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Ablation - A collective loss of water from an ice

sheet or glacier. This loss can take a variety of

forms. It is more dominant in the lower parts of a

glacier and in summer (due to warmer temps)

low altitudes.

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Accumulation - The net gain in an ice mass.

This gain can take place in a number of ways: precipitation,

refreezing of meltwater; avalanches etc.

It is more dominant in the upper part of the glacier and in

winter (due to lower temps) and where high altitudes.

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GLACIAL BUDGET - the net balance/change in the ice mass of a glacier.



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ZONE OF ACCUMULATION - the area on the glacier where accumulation exceeds ablation over 1 year

ZONE OF ABLATION - the area on the glacier where ablation exceeds accumulation over 1 year

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Ice Age - An extended period of time where the

Earth experienced a cycle of very cold phases

(known as glacials) interspersed with warmer

phases (known as interglacials).

The most recent ice age is called the Pleistocene

Ice Age, began 2 million years ago.

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Glacial - A very cold phase where global temps

dropped by approx. 5 degrees resulting in ice

covering 30% of the Earth's surface.

The most recent advance was the Devensian.

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Interglacial - A warm phase where temperatures

increased to present levels or above which only

lasts tens of thousands of years.

The most recent retreat was the Ipswichian.

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Cold (polar) glaciers - Where the base

temperature is well below 0 degrees and so

remains frozen to the bedrock. Found in polar

regions. e.g. Greenland, Antarctica. 

Warm (temperate) glaciers - The base

temperature is around 0 degrees so it's not frozen

to the bedrock. Found in temperate climates

where there are obvious seasonal differences in

temperatures. E.g. The Alps (Europe) 

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Glacial erosion processes

Glacial abrasion - Eroding of the valley floors and sides by the scraping & scouring of rock fragments as they are dragged along by the glacier as it moves.

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Plucking - Where glacial ice forms around fractured rock at the base or sides of the glacier. As the ice attatches to both the glacier and rock fragments, when the glacier moves it causes the rocks to be pulled away with it. 

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 Freeze thaw weathering - A process of mechanical weathering in rocks which contain joints or cracks where the temps fluctutate around 0 degrees. When it's warm water will enter joints & then freeze when temps fall below 0 degrees. As the water freezes it expands by 9% which exerts pressure in the joint causing it to widen. This is a repeated processes of melting & freezing. Can lead to breaking of the rock.

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Glacial deposition processes

Ablation Till - Material that is left by the glacier as it retreats. It is the scattering of angular, unsorted debris which has 'melted out' of the ice as the snout retreats up the valley. (If the snout remained stationary then the would build up to form a moraine)

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Lodgement Till - A form of ground moraine which is deposited under a glacier/ice sheet. It can result in a drumlin forming.

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Erratics - A rock which has been transported by a glacier or an ice sheet and deposited in an area of different geology to that of its source. An erratic can be an indication of the direct of the ice sheet. E.g. Norber Moor erratics, North Yorkshire.

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Till - Is an unsorted mixture of clay, sand, gravel &

boulders which are deposited directly from the

moving ice. Till deposits can vary considerably in

sediment structure, orientation and size -

reflecting the different processes involved in their


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Ablation till - Material which is left behind by the

glacier as it retreats. It's a scattering of angular,

unsorted debris which has melted out of the ice

as the snout retreats up the valley.

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Lodgement till (ground moraine) - Subglacial

material deposited by the actively moving glacier.

Form of moraine which is deposited under the

glacier. The rock particles are laid down under

the pressure of the slowly moving ice when the

base melts. The till stones may display some

orientation with the long axis in the direction of ice


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Describing glacial till deposited directly by the ice:

  • Unsorted, Not stratified, Not graded & Angular (not rounded) 
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Moraine are ridges of debris that develop along the margins of glaciers in response to the dumping of sediment that has been transported to the front and edge. 

End moraine - Moraine found at the snout of the glacier. (Umbrella term for 3 main types: recessional, terminal & push moraine)

Lateral moraines - Along the valley sides. Formed from debris drived from frost shattering of valley sides and carried along the edges of the glacier. 

Medial moraines - Found in the centre of a valley amd results from the merging of two lateral moraines where 2 glaciers have joined. Orientation of the till is in the direction of the glacial advance. 

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