Glacial Landscapes - Periglacial Processes

Periglacial environments are characterised by the large amount of angular rock which lies strewn across the land surface.

The angular shape of the material suggests that rock fracturing is responsible for its creation and regular freeze thaw processes are at work. Extensive areas of angular rock are called felsenmeer. The temperature is critical in developing this landscape: between -4 and -15 degrees Celsius.

Periglacial ground surfaces are influenced by ground ice, which is why the permafrost is an important feature in many periglacial areas. The most common type of ground ice is pore ice, which develops in the spaces between particles of soil. Needle ice is also important and are slices of ice that penetrate down through the soil. Needle ice is particularly important as it loosens soil particles, making them available for erosion and mass movement. Needle ice encourages the process of frost creep, which is where soil particles on a slope show a dominant movement downhill under the force of gravity. Particles are dislodged and elevated by the expansion of freezing ground and when the ground thaws the particles drop back down even further on the downslope side.

Frost heave also occurs, whereby the ground freezes and pushes material upwards with ice expansion, creating indentations on the ground. This continual process can result in loosened material on the surface.

As well as the mass movement process of frost creep, other types include solifluction, gelifluction and rockfalls.

• Solifluction – slow downslope flow of saturated soil, often forming lobes of movement and terracettes.
• Gelifluction – a periglacial category of solifluction where the downslope sliding movement of seasonally thawed and saturated soil material is facilitated by an impermeable layer of permafrost beneath.
• Rockfalls – frost shattering loosens materials on steep rock faces and it falls under the force of gravity.

Processes of erosion also take place in periglacial areas. Nivation is the name for a group of processes which carve out depressions in the ground. Snow builds up in a sheltered/shaded natural shallow depression and even in the warmer summer months, the snow doesn’t melt as often, even in warmer months, temperatures don’t exceed 0 degrees Celsius. During the winter, further snow falls and pressure turns the snow into neve/firn ice. Freeze thaw weathering occurs at the edge and along the bottom of the depression, creating loose material. The weathered material is then removed from the bottom of the feature by gelifluction.

Eolian erosion is a result of strong winds which are characteristics of periglacial regions. Winds often move large amounts of loose, unconsolidated particles and sediments. With very little vegetation to bind and protect surfaces combined with drying air conditions, there is much exposure of fine, loose material that has been deposited in outwash plains. The amount moved can vary across the year. More material is wind-blown during the summer months as the melting of snow and ice allows for looser drier material to be available on the ground. Deposits of wind-blown, fine, soil particles can lead to the accumulation of loess soils many hundreds of kilometres from their source.

Fluvial erosion also takes place but is seasonal. During winter months when most water is stored as snow and ice, streams are non-existent, whereas in the summer months’ rivers will appear. The differences in seasonal discharge is vast. The concentration of the discharge in a short time period creates some particular features. These short-lived streams tend to have poorly developed shallow braided channels. When discharge is suddenly reduced, large quantities of gravel and boulders are left on the landscape where the flow was taking place. Another characteristic of periglacial streams is that their channels can be braided with deep pools. Braided channels develop when a stream passes over a network of ice wedges and the river flow divides into several interlinking river channels. Heat from the flowing water causes the ice wedges to melt, producing the pools.