Cold Environments

Cold environments- usually are: icy landscapes, that occur in high latitudes and high mountain areas. They have extremely cold temperatures, an abundance of snow & ice with little vegetation. These areas are sparsely populated. (They generally occur in the polar regions and areas reffered to as the Alpine regions.)

Glacial environments - are the areas covered by ice sheets and glaciers. The largest of these is Antarctica and its sourrounding iceshelves. The other major glacial area is Greenland.

Periglacial and Tundra Regions - these exist in high-latitude areas and are not permantaly covered by snow & ice. The conditions create permantly frozen ground known as permafrost and the vegetation is sparse in such areas. Examples of these areas iclude: northern alaska and canada, northern scandanavia, siberia and the islands of the Artic Ocean such as Spitsbergen.

Alphine Regions - such areas may contain small ice caps, mountain glaciers and tundra environments. These environments include places such as: in Asia (Himalayas, Karakoram, Tibet plateau), Europe (Alps, Norwegian mountains), Australasia (Southern Alps in New Zealand) and the Americas (Rockies, Andes, Cascades).

How Ice Forms-

when the climate starts to becomes colder, more percipitation in winter falls as snow. Summers also begin to shorten, so there is less time for winter snow to melt. At first this leads to permanent snow cover in upland areas, the lower edge of which is know as the snow line. As the climate continues to deteriorate, the snow line moves down the slope. In the Northern Hemisphere, the snowline is found at higher altitude on the south-facing slopes than those on the north, as the south-facing recieve more instulation.

Snow initially falls as flakeswhich has an open feathery structure that traps air. As the snow accumulates, compression by the upper layers gradully turns the lower snow into a more compact form called firn or neve. Meltwater seeps into the gaps and then freezes, further compacting the mass. As more snow fall, air continues to be squeezed out of the lower snow by the weight of the upper layers, and after a period of years a mass of ice develops. Where there is no summer, melting, this process takes longer. During this period, the mass changes colour from white - indicating the presence of air, to bluish - indicating that the air has been largely expelled. This is the ice that begins to flow downhill as a glacier.

There are two types of glaciers - Temperate & Polar. The characteristics of each determine ice movement and affect glacial processes.

Temperate (alpine) glaciers - these melt in the summer, releasing huge amounts of meltwater, which then acts as a lubricant reducing friction. Temperate galciers move by basal flow, extending/compressing flow, creep and surges. These types of glaciers are more likely to erode, transport and deposit material.

Polar glaciers - occur in areas where the temperature is permantly below zero, therefore no melting occurs. Movement is slower as they are frozen to their beds and thus move mainly by internal flow. Much less erosion, transportation and deposition occurs.

As ice moves dowhill it has great ridgitiy & strengh but under steady pressure it behaves as a plastic body. This gives two zones within the glacier:

1- the upper zone - where the ice is brittle, breaking apart to form crevasses.

2 - the lower zone- which has steady pressure. Meltwater resulting from the pressure & friction allows a more rapid, plastic flow. At depth in the glacier the melting point of the ice is raised slightly by the increased pressure. Basal ice therefore is more likely to melt at temperatures close to zero.

Compressing flow- which occurs when there is a reduction in the gradient of the valley floor leading to ice deceleration and a thickening of the ice mass. At such points ice erosion is at its maximum.

Extending flow- which occurs when the valley gradient becomes steeper. The ice accelerates & becomes thinner, leading to reduced erosion.

Basal flow (sliding/slippage)- as the glacier moves over the bedrock there is friction. With the lower ice being under so much pressure plus the friction this causes some melting. The resulting meltwater then acts as a lubricant enabling the ice to move more rapidly.

Surges- occur from time to time when a excessive amount of meltwater under the glacier leads to the ice moving forward rapidly. These are hazardous to local people living near to the snout.

Internal flow- occur when ice crystals orientate themselves in the direction of the glaciers movement & slide past each other. As surface ice moves faster, crevasses develop. Internal flow is the main feature of the flow of polar glaciers as without the presence of meltwater, they tend to be frozen to thier beds.

Creep- occurs when stress builds up within a glacier, allowing the ice to behave with plasticity& flow. Especially when obstacles are met.

Rotational flow- occurs within the corrie, the birthplace of many glaciers. Ice moving downhill can pivot about a point, producing a rotational movement. This combined with increased pressure within the rock hollow leads to greater erosion and a over-deepening of the corrie floor.

A glacier can be viewed as a system with inputs, stores, transfers & outputs.

Inputs- are percipitation in the form of snow & ice, and avalanches with add snow, ice and debris from the valley side.

Storage- is represented by the glacier itself.

Transfers- is the way in which the ice moves.

Outputs- are water vapour, calving (formation of icebergs), and water in liquid form from ablation. The debris deposited at the snout i.e. moraine.

The upper part of the glacier where inputs exceed outputs and therefore where more mass is gained than lost over a year is know as the zone of accumulation.

The lower part where outputs exceeds inputs and where the mass is lost rather than gained over a year is know as the zone of ablation.

Between the two zones is the line of equilibrium of which seperate net loss from net gain and represents the snow line on the glacier.

The net balance is the difference between the total accumulation and the total ablation during one year. In temperate glaicers, there is a negative balance in summer when ablation exceeds accumulation and the reverse in winter. If the summer and winter budgets cancel each other out the glacier appears to be stationary.