Periglacial: Meaning, Processes And Landforms

Periglacial is referred to the areas at the periphery/edge of the glacier. It is characterized by low temperature. Its annual mean temperature is around Zero Degrees Celsius. It’s the summer season, and the surface is free from ice but subsurface water is found in the frozen state.

The landscape is the surface of the earth, as we observe while being in the field. It is basically the appearance of the land. Many agents of erosion sculpture the land itself. Depending upon the processes of sculpturing, the landscapes are different. Periglacial landscapes refer to the land features developed due to the process of peri-glaciation.

Periglacial Conditions

A periglacial condition exists in the peripheral areas of the glaciated regions. In this zone, the annual average temperature is around zero degrees Celsius. In winter, there is a thin layer of ice and snow accumulation, but it is not the same during summer days. Even during summer days, the subsurface moisture content is found to be in a frozen condition.

In the soil zone, the temperature is less than zero degree Celsius. Freezing and thawing are normal conditions which is the main cause of weathering here. Both glacial and periglacial conditions are quite different from each other.

Periglacial Landforms

Periglacial refers to the area in the periphery of the glaciated region. During summer, the region is almost free from ice on the surface, but the subsoil is still frozen throughout the year. This is very clearly seen in Figure, and a thin layer of snow and ice accumulation in Figure No. 22B.

The seasonal freezing and thawing of the subsoil is a regular feature of the region. During winter, the surface witnesses heavy snowfall and ice accumulation.

In other words, the area is almost permanently frozen but without permanent surface ice cover. The mean monthly temperature is between minus one degree to minus 15 degrees Celsius. The periglacial areas change with the change in the climatic condition prevailing on the planet.

Frozen Subsoil Water in Permafrost Area
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Thin Layer of Frost/ Snow in Permafrost Area
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Based on the extent of the freezing conditions, the permafrost areas are classified into three groups – continuous permafrost, discontinuously permafrost, sporadic permafrost and isolated permafrost. The surface layer, where freezing and thawing are seen, is known as an active layer.

Periglacial Processes

The periglacial areas witness several important processes: frost action, frost heave, and frost shattering, indirectly leading to rock fall, earthflow and debris flow.

Frost Action: It is obvious that the ice volume is greater than that of water. Freezing and thawing are natural processes. The water laying in the pores/ cracks or openings expands and breaks the rocks when it turns into ice. Therefore, weathering process is amplified by this process.

Frost Heave: When the subsoil water freezes, it leads to upward swelling of the top soil. This process is repeated time and again with changing seasons. Upper soil is loosened and subject to removal easily.

Frost Shattering: The freezing and thawing process is known as frost shattering. The water laying in the cracks of exposed rocks in cold climates leads to breaking them.

Rock Fall: Rock-fall is a type of mass movement in which the fragmented rocks tumble down almost freely. In cold climates, the exposed rocks are fragmented by freezing and thawing action, and hence, the credit of rock-fall is credited to permafrost action.

Earthflow and Debris Flow: The availability of water content liquefies the soil, and if it is on the slope, it flows quickly. This action is seen in the periglacial areas as the meltwater of ice triggers it. Debris flow includes unconsolidated soil, rock fragments, remnants of biotic life, and water. When these are associated with the slope, it leads to debris flow, and it is also triggered by water made available by snow melt in periglacial areas.

Periglacial Landforms

Several types of landforms are found in the periglacial areas. Some of them are:

Patterned Ground

Patterned ground is termed to that ground surface when the laying materials are distributed in a certain pattern. The pattern may be of any kind like stripes, ovals, circles, or polygons, particularly in the periglacial areas. They are made by frost heave action (Figure).

Ice Wedges

The wedges are pieces or slices or blocks. When the rocks are broken into pieces due to ice action, it is termed ice wedges. In this situation, the water or ice penetrates vertically into the surface for several meters.

In cold climates (periglacial areas), the seasonal freezing and thawing cause the rock to break and penetrate further down during summer. In winter, it freezes, and further, the space is widened, leading to rock breaking.

Blockfields

Blockfields are areas of huge expanse constituting the freeze-thaw weathered angular rock blocks in periglacial areas. Rock blocks get disintegrated into smaller pieces, and thus, angular rocks are seen on the surface (Figure).

Pingos

Pingos are hills of earth and gravel in dome-shaped formed in the periglacial areas under which the subsoil water freezes and tends to push the upper part upward. Its height may vary from 5 meters to 70 meters, and the diameter from 30 meters to one km. Most of the pingos are circular in shape.

Periglacial: Meaning, Processes and Landforms

Periglacial Conditions

Periglacial Landforms

Periglacial Processes