Glacier models

Definition: a mathematical reconstruction of the dimensions and flow of a present or former glacier
 
Glaciers are plastic solids that rest on a slope and flow by sliding, deformation and creep. The rate and pattern of flow is influenced by many variables, including slope, relief, ice thickness and ice temperature. The latter variables can be linked to climatic factors, such as air temperature and snowfall. The dimensions of a glacier reflect the balance between accumulation and ablation (melt). Today many glaciers around the world are retreating because global warming is leading to lower snowfall (more rain) and higher ablation (due to higher summer temperatures). Conversely, glacier advance during cold stages of the Pleistocene represented the net build up of glacier ice.
 
Studies of modern glaciers has allowed equations to be developed and tested that represent the behaviour of glaciers. The flow of a glacier can thus be modelled provided certain parameters are known. The relief and slope of the glacier come partly from the terrain, although ice surface slope is always smoother than valley slope. Ice thickness can be computed from glacier surface profiles if the location of the ice margin is known. Accumulation and ablation rates are more tricky and are generally estimated by reference to regional climate proxies - ice and ocean cores and palaeoclimatic reconstructions based on pollen, beetles or midges preserved in organic sediments beyond the glacial limits.
 
This type of modelling has been used in the Cairngorms to examine the controls on the distribution of warm-based and cold-based ice (Hall and Glasser, 2003). Although the modelling is crude, it suggests that the shape of the preglacial terrain was a fundamental control on the location of basal sliding and erosion. In deep preglacial valleys, like the ancient Glen Avon, the valley was sufficiently deep and steep to induce basal ice to rise to its pressure melting point and to begin sliding. This generated frictional heat and this, together with the draw down of ice towards the valley beneath the Cairngorm ice sheet, ensured high rates of erosion and the development of a glacial trough.