explain (v)

  1. give a detailed account including reasons or causes.


hummock (n)

  1. A hummock is a small hill or mound above ground. They are typically less than 15 meters in height and tend to appear in groups or fields. 

periglacial (adj)

  1. relating to or denoting an area adjacent to a glacier or ice sheet or otherwise subject to repeated freezing and thawing.

regolith (n)

  1. Regolith is a layer of loose, heterogeneous superficial material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons.


Permafrost is ground that remains continuously at or below 0 degrees Celsius for at least two consecutive years.

Global distribution of permafrost



Patterned ground is the distinct, and often symmetrical geometric shapes formed by ground material in periglacial regions. Typically found in remote regions of the Arctic, Antarctica, and the Australian outback, but also found anywhere that freezing and thawing of soil alternate; patterned ground has also been observed on Mars.



Partially melted and collapsed lithalsas (heaved mounds found in permafrost) have left circle-like structures on the Svalbard Archipelago (Wikipedia)



Solifluction is the slow downslope movement of water-saturated sediment due to recurrent freezing and thawing of the ground, affected by gravity.  

It occurs in late summer, when the ice-rich layer at the bottom of the active layer thaws to form a plastic mud. Moving almost imperceptibly on the plastic layer, this saturated soil is deformed into solifluction terraces and solifluction lobes that give the tundra slope a stepped appearance

What happens when permafrost thaws?

Solifluction Lobes in the Swiss National Park, Graübunden.




Thermokarst is a land surface characterised by very irregular surfaces of marshy hollows and small hummocks formed as ice-rich permafrost thaws. Thermokarst occurs in Arctic areas, and on a smaller scale in mountainous areas such as the Himalayas and the Swiss Alps.

Thermokarst at Jackson Hole Valley, Teton National Park, Wyoming, USA



A pingo, also called a hydrolaccolith, is a mound of earth covered ice found in the Arctic and subar-ctic that can reach up to 70 m in height and up to 600 m in diameter. The term originated as the Inuvialuktun word for a small hill. The plural form is "pingos".

Pingo National Landmark, Canada



  1. Complete the following grid using information from above and p 85 of the study guide