Periglacial Landforms and Periglacial Landforms and ProcessesProcesses

Periglacial areas are those that experience a cold climate, with intense frost action and the development of permafrost.

Areas of permafrost in North America

Continuous permafrost – little thawing even in summer

Permafrost is permanently frozen ground. There are three main types:

Discontinuous permafrost – breaks in permafrost around water eg lakes

Sporadic permafrost – permafrost only in isolated spots

Ground Ice: A key characteristic of permafrost is the presence of ice in the upper tens of meters of the permafrost. This ice occurs in many forms and often in large masses of relatively pure ice. The widespread presence of ice in permafrost creates challenges for construction since when the ice melts the ground becomes unstable

Buildings constructed in areas affected by permafrost need to be insulated from the ground. Tried and tested techniques include placing the building on wooden piles. This photograph shows a corner of the SAS/Radison Hotel in Longyearbyen, Svalbard. Although the area between the piles is boarded off, it is maintained at air temperature as the building above is fully insulated.

Most services, such as water and sewerage, need to be insulated both from permafrost and sub-freezing winter temperatures. They are commonly placed on wooden stilts above ground level. Thickly insulated plastic piping replaces the old metal conduit. Some have a heating element running through them.

Periglacial Processes: WeatheringPeriglacial Processes: WeatheringLocations that have a periglacial environment are characterized by the presence of large quantities of angular, fractured rock. The quantity of the deposits indicates that the frost weathering process operates over and over again in repeated cycles of freeze-thaw.

This is a close-up of frost-shattered bedrock, consisting of angular blocks of granite. Extensive areas of blocks are called felsenmeer. The shattering has occurred in permafrost terrain, near treeline.

Northern Manitoba, Canada

Nivation hollow

North facing snow patches

Nivation Nivation takes place beneath patches of snow in hollows, particularly on north- and east-facing slopes.

Freeze-thaw action operating under the snow causes the underlying rock to disintegrate.

Over some period of time, this leads to the formation of nivation hollows which, when enlarged, can be the beginnings of a corrie.

Solifluction Solifluction is the slow, downslope creep of fine-textured soils.

Solifluction leads to the formation of lobate-shaped debris masses or solifluction lobes.solifluction lobes.

Frost creep is the slow downslope movement of soil and sediment because of frost heaving and thawing. The process begins with the freezing of the ground surface elevating particles at right angles to the slope. The particles are elevated because cold temperatures causes water in between particles to freeze and expand. In the warm season,

thawing causes the ice to convert back to liquid water and the contracting surface drops the particles in elevation. This drop, however, is influenced by gravity causing the particle to move slightly downslope.

Frost-sorting on slopes results in stone stripes. In this example the scree slope provides a steady supply of angular rock fragments, which are then sorted as the material is carried down to the wetter more muddy ground below.

Frost-sorting on level stony ground produces stone circles, such as this one in Svalbard. The outside diameter is approximately 1m.

Frost-sorting in areas where snow-melt is trapped and mobilises mud-rich glacial sediment, yields stone polygons as here in northwestern Spitsbergen. The stone ridges make for firm walking, but boots can be overtopped if they sink into the fine material in the middle of the polygon.

Ice Ice WedgeWedgess

Closed-system pingospingos are found most commonly in areas of low-lying, poorly drained terrain in regions of continuous permafrost. In such regions, bodies of unfrozen ground exist beneath the larger water bodies such as lakes and rivers. When a lake drains newly exposed sediments of the lake-bed cool, and permafrost begins to grow in this unfrozen soil. As the freezing and heaving continues over time a mound is formed which continues to grow. The largest closed-system pingos known are about 50-m high.

Exposed ice core of an eroded pingo.

Collapsed pingo

Closed pingo

Summary - Features produced by periglacial processesSummary - Features produced by periglacial processes