146
Climatic Geomorphology
characterized by a strong frost action, a limited runoff influence and significant wind
activity.
(b) Cold and wet climates with strong winters. The arctic and mountain types are
differentiated within this group. The arctic type has large climatic irregularities due to
the oceanic influence and has permafrost. The temperatures are similar to climate
A with a lower annual range, precipitation is above 300 mm, and violent winds are
common. Consequently the frost action is less intense or persistent than in climate A,
the snow cover inhibits eolian processes, and run-off is relatively important. The
mountain type occurs in the alpine areas of the temperate zones. Temperatures are
similar to the arctic type with higher mean annuals and lower annual ranges.
The annual precipitation is higher than in the arctic type. The role of slope and aspect
are very important in these areas. Therefore, frost action is important, permafrost
is generally absent, the wind influence is weak, and run-off-related processes are
conspicuous.
(c) Climates with small annual range in temperature. The mean temperature is close to
0~ and the annual temperature range is around 10~ Two types are distinguished.
The climate of high latitude islands has marked weather instability, small temperature
range, and snow precipitation above 400 mm that inhibits the effects of the wind.
Freeze-thaw cycles are abundant and have limited penetration into the ground. The
low latitude mountain climate types lack seasonal temperature variations and the daily
range is very high and larger than the annual range. Precipitation is commonly high,
except in the arid mountains. These climatic conditions engender the existence of
permafrost, numerous freeze-thaw cycles, faint penetration of the frost action, and
insignificant wind activity except in arid mountains.
In addition, the periglacial domains present two main types of vegetation, the subarctic
or northern forest, and the arctic tundra. This allows distinguishing between the forest
periglacial environments and the woodland-free environments (French, 1996).
2. Permafrost
Permafrost, also called pergelisol or permanently frozen ground, is defined as a soil,
surficial deposit or rock mass that remains continuously below 0~ for more than 2 years,
regardless of other properties like the moisture content and lithology (Muller, 1945).
Glaciers and ice-sheets are excluded. Permafrost covers around 22% of the land surface in
the Northern Hemisphere and extensive areas in the Andes and Antarctica (Harris, 1986).
According to Washburn (1979), 14% of the land surface on the Earth is underlain by
permafrost. It extends as far as 50% of Canada and 80% of Alaska (Harry, 1988).
Permafrost also occurs in the bottom of shallow seas in high latitudes (submarine
permafrost). Two types of permafrost occur on the continents; polar permafrost in high
latitude areas and alpine permafrost. Alpine permafrost is developed in mountain
environments and varies depending on the latitude and elevation. The altitudinal lower
limit of the permafrost rises from high to low latitudes (Harris, 1988).
The continuous permafrost wedges out towards low latitudes and breaks up into
patches giving way to the discontinuous and sporadic permafrost (Harris, 1986)
Climatic Geomorphology
characterized by a strong frost action, a limited runoff influence and significant wind
activity.
(b) Cold and wet climates with strong winters. The arctic and mountain types are
differentiated within this group. The arctic type has large climatic irregularities due to
the oceanic influence and has permafrost. The temperatures are similar to climate
A with a lower annual range, precipitation is above 300 mm, and violent winds are
common. Consequently the frost action is less intense or persistent than in climate A,
the snow cover inhibits eolian processes, and run-off is relatively important. The
mountain type occurs in the alpine areas of the temperate zones. Temperatures are
similar to the arctic type with higher mean annuals and lower annual ranges.
The annual precipitation is higher than in the arctic type. The role of slope and aspect
are very important in these areas. Therefore, frost action is important, permafrost
is generally absent, the wind influence is weak, and run-off-related processes are
conspicuous.
(c) Climates with small annual range in temperature. The mean temperature is close to
0~ and the annual temperature range is around 10~ Two types are distinguished.
The climate of high latitude islands has marked weather instability, small temperature
range, and snow precipitation above 400 mm that inhibits the effects of the wind.
Freeze-thaw cycles are abundant and have limited penetration into the ground. The
low latitude mountain climate types lack seasonal temperature variations and the daily
range is very high and larger than the annual range. Precipitation is commonly high,
except in the arid mountains. These climatic conditions engender the existence of
permafrost, numerous freeze-thaw cycles, faint penetration of the frost action, and
insignificant wind activity except in arid mountains.
In addition, the periglacial domains present two main types of vegetation, the subarctic
or northern forest, and the arctic tundra. This allows distinguishing between the forest
periglacial environments and the woodland-free environments (French, 1996).
2. Permafrost
Permafrost, also called pergelisol or permanently frozen ground, is defined as a soil,
surficial deposit or rock mass that remains continuously below 0~ for more than 2 years,
regardless of other properties like the moisture content and lithology (Muller, 1945).
Glaciers and ice-sheets are excluded. Permafrost covers around 22% of the land surface in
the Northern Hemisphere and extensive areas in the Andes and Antarctica (Harris, 1986).
According to Washburn (1979), 14% of the land surface on the Earth is underlain by
permafrost. It extends as far as 50% of Canada and 80% of Alaska (Harry, 1988).
Permafrost also occurs in the bottom of shallow seas in high latitudes (submarine
permafrost). Two types of permafrost occur on the continents; polar permafrost in high
latitude areas and alpine permafrost. Alpine permafrost is developed in mountain
environments and varies depending on the latitude and elevation. The altitudinal lower
limit of the permafrost rises from high to low latitudes (Harris, 1988).
The continuous permafrost wedges out towards low latitudes and breaks up into
patches giving way to the discontinuous and sporadic permafrost (Harris, 1986)