Where and when do glaciers occur?

Glaciers accumulate wherever there is a surplus of snowfall over snowmelt for enough years to allow the consolidation of snow into ice. Given a specific threshold of thickness (which varies according to the slope) the ice starts to move downslope. The pressure of the moving ice, together with the loose material it picks up, erode the land surface and scour the bedrock beneath the glacier and the slopes at the glaciers margins.
When the rate of melting exceeds that of ice accumulation the glacier margins retreat and deglaciated substrates are exposed.

Glaciers occur in a wide range of arctic and alpine environments. Most cold areas of the world show signs of having been eroded by glaciers at intervals of between 20,000 and 50,000 years. So this type of disturbance acts on a very different time scale, compared to the others described in this unit. Furthermore, it operates on a very large scale and affects alpine environments in all parts of the world.
In addition to major changes associated with long-term shifts in climate, most glaciers show signs of shorter term advances and retreats so that the zone at the glacial margin is regularly disturbed.

1 - Rotmoosferner
1 | 2 (108-121K each)

Rock glaciers

Rock glaciers develop where there are particularly thick accumulations of rocky debris e.g. on large talus slopes, and when low soil temperatures cause meltwater to seep into the pores in the debris and freeze. The ice filling the pores in the debris allows a glacier-like movement of the debris, producing long tongues of broken rock.

What are the consequences?

Direct disturbance by the glacier results in erosion as well as the deposition of debris from glacier ice. It is often accompanied by rock slides and slumping of lateral moraines when the glacier retreats.
The recently deglaciated terrain is also a very disturbed environment which is still strongly affected by the presence of the glacier. The bare sediments are often saturated with meltwaters from the glacier and are susceptible to mass movements, freeze-thaw and wind erosion. These areas are also affected by meltwater streams and glacier winds.

2 - Valleybottom (134K)

29 August 2011
© ALPECOLe 2002-2007