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. 


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

  1. Diurnal temperature ranges go above and below zero degrees,
  2. The repeated freezing and thawing of groundwater forces larger stones toward the surface as smaller soils flow and settle underneath larger stones.
  3. Areas that have many larger stones contain much less water than areas of finer grained sediments.
  4. Areas of finer sediments are saturated with water
  5. Areas of finer sediments expand and contract as freezing and thawing occur, more than areas with large stones
  6. This leads to lateral forces which ultimately pile larger stones into clusters and stripes.
  7. Through time, repeated freeze-thaw cycles smooth out irregularities and odd-shaped piles to form the common polygons, circular, and stripes of patterned ground.


Solifluction literally means flowing soil. It is the slow, downslope movement of water-saturated sediment due to repeated freezing and thawing of the ground, affected by gravity.  

Solifluction lobes in the Swiss National Park, Graübunden.

How is it made?

  1. In winter, the soil and water in the soil freezes.
  2. In spring, the upper layer of the soil melts (active layer), releasing water.
  3. The water infiltrates the upper layer of soil but cannot penetrate deeper because of the frozen permafrost underneath.
  4. The water flows slowly downhill under the surface of the soil creating solifluction terraces and solifluction lobes

What happens when permafrost thaws?




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