Australia: The Land Where Time Began

A biography of the Australian continent 

The Cryosphere - Glaciers & Ice Sheets

The author¹ says glaciers are 'perennial ice masses that are large enough to experience gravitational deformation: the flow of ice under its own weight'. Where the accumulation of snow exceeds the ablation rate of that snow over an extended period of many years to decades glaciers and ice sheets nucleate. The snow is buried over time as snow continues to fall upon it, the weight of the additional snow compressing and compacting lower levels of the snow until it is transformed into the ice of a glacier. Once the ice is of sufficient thickness for the internal  gravitational stresses to cause deformation of the ice it behaves as a nonlinear, viscoplastic fluid.

Mountain glaciers have formed in many places around the world, even in the tropics, wherever there are alpine regions, such as in the high mountains of tropical latitudes of  East Africa, South America and New Guinea. The many types of mountain glaciers, mainly being classified according to the topographic setting, cirque and valley glaciers are prominent among them. There are ice masses that are independent and self-sufficient in  an alpine niche, valley glaciers can be outlet glaciers draining nêvés (icefields), long sloping areas of snow accumulation covering mountain peaks or plateaus at high altitude. Ice fields conform to the topography, having high peaks above the ice surface at the perimeter of the icefield and within the ice mass. These peaks or ridges standing above the surface are nunataks. The shape and extent f icefields, as well as their direction of flow, are determined by the structure of mountains separating them. This is what distinguishes icefields from ice caps, the latter overwhelming the topography beneath them, the ice flow being determined by the geometry of the ice cap.

An ice sheet is an ice cap on a continental scale, size being the only glaciological distinction, and the ice sheets of Antarctica are more than 2 orders of magnitude larger than the largest ice caps in the world. They warrant special attention because of their role in the world's climate.

Sources & Further reading

1. Marshall, Shawn J., 2012, The Cryosphere, Princeton University Press.

Cryosphere