An introduction to periglacial environments

Having made a lot of progress with my learning of glaciers I am now going to move on to looking at periglacial environments, including processes and landforms.

To begin with, it is important to know exactly what periglacial means. Looking at a variety of websites:

A periglacial environment originally referred to areas bordering glacial areas, but has now been extended to refer to those areas with a tundra climate. This includes mountainous areas in the mid-latitude regions or where frost processes and permafrost occurs. This definition includes approximately 20% of the earth’s surface.

Periglacial environments can be found on the edges of polar or glacial environments, for examples areas of Siberia, Greenland and Canada. It is also important to include that periglacial environments usually have a seasonal temperature variation with mean summer temperatures usually rising above 0°C for a certain period.

Now that we have a definition of periglacial environments, it is important to look at the key words within the definition.

Permafrost

Permafrost is ground that remains frozen that stays at or below 0°C for two or more years and occurs in areas where the mean annual temperature is colder than 0°C. It is not solely found in cold landscapes, but can also be found in low latitude regions with areas of high elevation. This is known as alpine or mountain permafrost and can be found in the Rocky Mountains and the Andes. This kind of permafrost can occur at elevations as low as 8,000 feet.

The thickness of permafrost is dependant on a variety of variables: snow cover, vegetation cover, the temperature of the air near the ground, bodies of water and the heat from the interior of the Earth. The active layer of permafrost is the uppermost ground layer which thaws in the summer and freezes in the winter. When vegetation is present, it is restricted solely to this layer as roots cannot break through the frozen ground below.

The map above shows the extent of permafrost on a global level. Showing the map to students would be good to not only illustrate the extent of permafrost but to help with global locational knowledge (e.g. mountain ranges shown on the map)

There can be two types of permafrost:

Continuous – Regions with severe winters and temperatures below freezing leading to permafrost underlying nearly all of the landscape (except rivers and deep lakes which don’t freeze to the bottom). The thickness of the active layer varies in accordance with the temperature – in colder areas, permafrost is topped with an active layer of less than a foot thick.

Discontinuous – Warmer regions where the mean annual air temperature is only slightly below 0°C and local variables determine whether permafrost is either formed or maintained. Discontinuous permafrost can be further split into two subdivisions:

            Extensive discontinuous – occurs in with mean annual temperatures ranging between –2°C and -4°C.

            Sporadic – occurs in areas with mean annual temperatures ranging between 0°C and -2°C.

Permafrost is often found in peatland areas as whether or not it forms is dependant on how well the surface is insulated from the soil and rock which lies below it. Peat has many properties which make permafrost formation possible. Dry peat is a brilliant thermal insulator and so in the summer it prevents the heat from reaching the ground. On the other hand, when peat is wet or frozen it is an efficient transmitter of heat from the ground into the atmosphere. Thus, discontinuous permafrost can be found in peatlands throughout North America, Europe and Asia.

The picture above is a good map to show permafrost extent in the Northern Hemisphere as well as the different types of permafrost that can exist within a variety of places. 

This introduction to periglacial environments is a necessary start to begin to look at the key terms. When teaching this, it would be good to show student the map so that is would be easier for them to remember the parts of the world where permafrost occur. With regards to the different types of permafrost, showing them pictures and asking them what type they think it would be will engage them with the topic and may be better than simply getting them to read a text book or copy off the board.

Links used:

http://ngm.nationalgeographic.com/geopedia/Permafrost - National Geographic

http://www.slideshare.net/rgamesby/11-periglaciation-areas - Types of permafrost

http://fds.oup.com/www.oup.com/pdf/oxed/Pages%20from%20aqa_as_ch02.pdf - Permafrost map

http://www.hazardz.co.uk/131GED/periglacial.pdf - Map of permafrost in Northern hemisphere