Permafrost is frozen ground that shapes ecosystems, landscapes, and human settlement in cold regions. This lesson introduces its definition, the annually thawing active layer, and the global pattern of permafrost.
Permafrost is soil, rock, or sediment that remains at or below 0 °C for at least two consecutive years. The term does not mean that every particle is ice: frozen ground can contain soil, rock, liquid water, and ice. Permafrost may be less than a metre thick or extend more than 1,400–1,500 m downward. The oldest known permafrost has remained frozen for about 700,000 years.
All flashcards
What is permafrost?
Soil, rock, or sediment that remains at or below 0 °C for at least two consecutive years.
What happens in the active layer?
It thaws during the warm season and freezes during the cold season. Plant roots generally grow in this layer rather than in the permanently frozen ground below.
What does the permafrost table mark?
It is the boundary between the seasonally thawed active layer and the underlying permafrost.
Thermokarst
Landforms created when ice-rich permafrost thaws and the ground settles or erodes.
Where is most of the world’s permafrost found?
In high northern latitudes, especially Siberia, Alaska, Canada, and Greenland, with additional areas in high mountains and beneath polar continental shelves.
Quiz questions
How long must ground remain at or below 0 °C to meet the standard definition of permafrost?Answer: At least two consecutive years.
What does the term thermokarst describe?Answer: Landforms produced as ice-rich permafrost thaws and the ground settles or erodes.
In oxygen-rich conditions, what gas does decomposition of thawed organic matter tend to produce?Answer: Carbon dioxide.
What is the purpose of heat pipes installed in supports on permafrost?Answer: To carry heat away from the ground.
Why does subsea permafrost occur beneath some polar continental shelves?Answer: Parts of the shelves were exposed land that froze when sea levels were lower.
Based on the Wikipedia article Permafrost, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.