by Michael Davis ’14

Permafrost is perennially frozen ground—sediment, soil, or sometimes water in bedrock that is frozen for many years (often up to thousands of years).[1]  Permafrost is characteristic of high latitudes, often found in northern North America, Europe, and Asia; however, permafrost is also found at high altitudes on mountain ranges at lower latitudes.  The top layer of the soil in a region that has permafrost may thaw during the summer, and freeze back during the winter.  This top layer is referred to as the active layer.  Understanding the active layer of permafrost regions is important for human infrastructure, as the active layer becomes very unstable when it thaws.  Thus, a house built on the active layer of a permafrost region may warm up the layer and cause a thawing event that could collapse the foundation of the house.  The same issue was taken into account when oil fields were discovered in Alaska, and a heated pipeline for the oil was created.  In order to avoid melting the active layer, and causing the ground to collapse, the pipeline was built on stilts above the ground to avoid contact with the active layer.  Permafrost degradation has been widespread and rapid in central Alaska, and has caused shifts in local ecosystems.  The ground collapse that results from permafrost thawing kills local birch trees in poorly-drained areas, resulting in the take-over of aquatic plants that create a mat covering that area.  Because of this process, it is estimated that by the end of the century, the central-Alaskan lowland birch forests will be completely eliminated.[2]  Thawing permafrost can also have detrimental effects on the local hydrology in some regions as well.  If permafrost thaws in well-drained regions, that water will drain out quickly and lead to a sharp decrease in ground water in that region.[3]

Permafrost degradation can become a problem for local ecosystems that have adapted to the environment that the permafrost has created.  Global temperature increase is correlation with permafrost degradation.  While this aspect of the cryosphere is less well known, the results of the loss of permafrost can be devastating to local ecology and ecosystems.