Around the fringes of ice fields there are areas which are cold but not covered permanently by snow or ice.
These are the periglacial areas:
- the modern Tundra of northern Canada and Siberia;
- and during the Pleistocene:
- southern England during the glacial periods;
- the whole of Britain during the interglacial periods.
The principal cause of periglacial features is the expansion/contraction of water/ice:
- expansion when water freezes to ice
- contraction when the ice gets colder, followed by expansion when it warms again.
This change in volume is very effective in
- breaking up rock to form scree and felsenmeer;
- forming stone polygons and other patterned soil.
In permafrost areas, the whole of the soil is frozen in winter, down to depths of hundreds of metres in some cases.
In summer, the top layers melt, forming an active layer of waterlogged soil. This fluid layer moves downhill on even
the gentlest of gradients, leaving solifluction (or 'head') deposits. The land surface tends to become levelled out
- and very marshy in summer.
Other areas beyond the fringes of ice-sheets are rocky deserts where wind takes advantage of a plentiful supply
of sand and silt sized particles to erode exposed rock surfaces.
In Britain, head deposits can sometimes be seen just below the soil in areas previously affected by permafrost
conditions. Hill slopes of upland areas are commonly covered in aprons of scree.
Geopix Study Topic "Periglacial Areas" (See below)
- gives full images of the examples shown below;
- explains how these periglacial features are formed, using additional images;
- gives images to illustrate periglacial features in Briatin;
- suggests how to answer exam questions on this topic.
The Periglacial Areas Study Topic contains the following pages:
'Periglacial Areas' is part of the Glaciation Guide CD.
To order this CD go to the Geopix Online Store
