Glaciation

In the past, there has not always been the same amount of ice on the surface of the planet. The amount of glaciation depends on what is termed the glacial budget. In the same way that a financial budget changes as money is accumulated and spent, the ice present in an ice sheet or an individual glacier changes as more ice is accumulated or lost. When there are higher levels of snowfall than melting, the quantity of ice increases and vice-versa. The glacial budget can be measured season by season or using longer periods of time like decades or centuries. Since the 1950s, the glacial budget for the whole Earth has been negative meaning that the world's glaciers are in retreat.

Ice is one of the most powerful forces that shapes our landscape and you need to be aware of the erosional processes of glaciation. These include freeze-thaw weathering and the processes of erosion caused by moving ice. As ice moves over a land surface, the front of the ice sheet or glacier will push loose material, including soil, ahead of it. This is termed bulldozing. At the other end of a glacier, in the cwm where the ice is forming, the 'bowl' of ice rotates slowly, causing erosion beneath it. As the ice moves downhill, as it passes over masses of bedrock, it abrades (rubs down like sandpaper) the leading surface then plucks fragments from the trailing (downhill) surface.

When a glacier melts, the material that is being carried on top of the glacier as moraines and within the ice, is left behind. Unlike river erosion, the rock pieces are unsorted and angular in appearance. These are deposited as unstable piles of rock fragments which gradually settle, consolidate and become colonized by plants and animals. The other key depostional feature of glaciation is a drumlin, or rather drumlins as they are usually deposited in groups called swarms.

Areas that are actively affected by snow and ice attract tourists and the winter sports industry is now well established in the more accessible mountain ranges like the Alps and the Rockies. There are always two sides to any human economic development and these winter sports areas need to be carefully managed to strike a balance between the economic needs of the resort, safety and caring for the environment.