Work of Ice
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• Every 200-250 million years, climatic activity leads to falls in temperature of over 5 degrees centigrade. These periods of great ice activity are known as Ice Ages.
• The most recent is the Pleistocene period of the Quaternary era, which began 2 million years ago. The earth only became warmer during the last 20,000 years.

  Reasons for fall in Earth's temperatures

• Movement of tectonic plates leading to an increase in the altitude at constructive margins.
• Changes in ocean currents
• Variations in sunspots changing the amount of radiation received by the earth
• Changes in level of atmospheric CO2.

  Glaciation

• Glaciation is the work of ice in a landscape.
• A glacier is a mass of moving ice confined in a valley.
• When air temperature falls to sub-zero, water vapor condenses and freezes to form snow.
• If the snow doesn't melt, a permanent snow covering is formed known as a snow line.
• If the accumulation of snow continues, the snow hardens into ice crystals separated by air spaces. Due to pressure, ice melts and water flows into the air spaces and re-freezes. This turns the snow into a granular mass known as a ne've or firn.
• Finally, all the air spaces disappear and a glacier is formed. Ice blocks may break off to form icebergs.

  Ice Movement

• Ice may move through one of these three processes:

1. Plastic Flowage: Ice has plastic qualities and may flow en-masse like a viscous liquid
2. Basal Slip: The process through which ice slips and slides over the underlying rock.
3. Internal Shearing: Movement similar to rock faulting involving differential sliding along planes.

• The speed of ice movement depends on the gradient of the slope and the thickness of the ice.

  Ice Erosion

• This involves three processes:

1. Plucking: Parts of the underlying rock are frozen into the base of the ice and pulled away.
2. Glacial Abrasion: The grinding process where stones frozen in the ice scrape and scratch against the underlying rock.
3. Sapping: The breaking of rocks by the alternate freezing and thawing of the ice at the bottom or sides of the mass.

Landforms of Glaciation

1. Cirques: Steep sided rock basins semi-circular in plan. Could develop into corrie lakes called Tarns.
2. Aretes: Steep sided knife edged ridge separating two cirques.
3. Pyramidal Peak: Jagged peak formed by the steepening of the back walls of several cirques on the sides of a mountain. Also called horns.
4. U-Shaped Valley: A broad flat-bottomed steep-sided valley with a U shape. Also called a glacial trough.
5. Fjord: A deep narrow arm of the sea with steep sided parallel walls.
6. Hanging Valley: A tributary of a U-Shaped Valley ending abruptly high above the floor of the U shaped valley and separated from it by an almost vertical slope.

Erosional Landforms

1. Rouche Moutonee: An outcrop of resistant rock smoothed by ice on the upstream into a gentle slope and plucked on the downstream end to give a steep jagged edge.
2. Crag and Tail: A knob of resistant rock (crag) which protects a weaker rock (tail) from ice erosion on the downstream slope.
3. Ice-Eroded Plain: An extensive area once covered by an ice sheet which smoothed off the original landforms to give a rounded topography.

Depositional Landforms

Those formed by unsorted materials:

1. Boulder Clay Plain: A monotonous hummocky plain made of clay and boulders and deposited haphazardly by ice sheets over a surface.
2. Drumlins: Elongated ovoid low hummock made of boulder clay.
3. Terminal Moraine: Ridge like feature made of boulder clay marking the edges of the ice.

Those formed by sorted fluvio-glacial materials:

1. Esker: Steep sided ridge made of gravel and sand.
2. Kame: An irregular shaped mass of stratified material formed as a delta on the surface of a stationery glacier.
3. Outwash: Made of gravel and sand and developed outside of the terminal moraine by melt waters from the ice depositing sorted materials.

Other Notes in this Category

1. Action of Ice
2. Deserts
3. Folding
4. Plate Tectonics and Continental Drift
5. The action of rivers
6. Vulcanicity and Landforms
7. Weathering
8. Work of Ice

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