Periglacial Landforms

Pingos

Description: They are dome shaped hills that can be up to 500m in diameter and 50m high. At the core, there is an ice lens and the surface is made up of soil and vegetation. The surface may be cracked. Formation: One way pingos are formed is where water is trapped in small depression in areas of impermeable permafrost. Over winter, ground water beneath lake sediments can be trapped by ice as the lake freezes. This decrease in temperature causes this ground water to freeze into an ice lens, which grows over time. This causes the sediment above to bulge upwards.

Patterned Ground

Description: They can be up to 5m in diameter. They have uneven ground and bulges surrounded by rock.Formation: Ice lenses form due to fluctuating freezing and thawing in the active layer, forming uneven ground. Water then migrates to the ice lens. The lens begins to grow and pushes rocks upwards. Due to the stones thermal conductivity, cold patches form beneath them which can push the stones further upwards. Larger stones roll down the bulges, forming stone rings.

Ice Wedges

Description: These are downward spikes of ice up to 3m wide and 10m deep.Formation: In the winter, cracks may form due to lack of moisture. At first, they may only be a few mm wide and a metre deep. In the summer, water may fill this crack which freezes as it reaches the freezing permafrost. Expanding ice increases the size of the fracture. After about 100 years, they can be around 3m wide and 10m deep

Nivation Hollows

Description: A localised, isolated patch of snow and ice that remains through the summer season.Formation: Snow patches accumulate on a slope with a north-easterly aspect and doesn’t melt. This causes physical weathering at the margins. Freeze thaw action occurs due to fluctuating temperatures, creating a mass of small rock fragments. This causes a hollow to occur, which may eventually form a corrie.