Pingos Formation

Question 1

What are Pingos?

Answer 1

• Pingos (Figure 2.29) are rounded ice -cored hills that can be as much as 90 m in height and 800 m in diarneter. They grow at rates of a couple of cm/year.
• They are essentially formed by ground ice which develops during the winter months as temperatures fall There are two types that are recognised

Question 2

Open-System Pingos

Answer 2

• Open-system pingos form in valley bottoms where water from the surrounding slopes collects under gravity, freezes and expands under artesian pressure. The overlying, surface material is forced to dome upwards. This type is common in east Greenland.

Question 3

Closed-System Pingos

Answer 3

• Closed-system pingos develop beneath lake beds where the supply of water is from the immediate local area As permafrost grows during cold periods, groundwater beneath a lake is trapped by the permafrost below and the frozen lake above. The saturated talik, or unfrozen ground, is compressed by the expanding ice around it and is under hydrostatic pressure. When the talik itself eventually freezes it forces up the overlying sediments. Over 1400 pingos of this type are found in the Mackenzie delta of Canada.

Question 4

Modifcation of landforms - Patterned ground

Answer 4

• Patterned ground is a relatively minor and small-scale feature. As temperatures rose at the end of the periglacial period, patterned ground was often colonised by vegetation, making it hard to find and identify. Over time mass movement by creep also degrades the frost-heaved domes, making the landform less obvious. Patterned ground around Leedon Tor, Dartmoor is now mainly covered by a layer of soil and grasses.

Question 5

Modifcation of landforms - Pingos

Answer 5

• Pingos collapse when temperatures rise and the ice core thaws. When this happens the top of the dome collapses leaving a rampart surrounding a circular depression called an ognip. Relict ognips can be found in Britain, although due to the thawing of the permafrost only the remains of the rampart may be seen. A good example, about 15 m in diameter, can be seen at Llanberis in north Wales.