Permanently frozen ground or “permafrost” is soil or rock that remains frozen (below 0 degrees C) throughout the year. Permafrost, which only occurs at the highest latitudes or at high elevations, has major influences on site hydrology, vegetation, and wildlife movements. Permafrost underlies about 45% of Denali National Park and Preserve, though some of this permafrost is within a few degrees of thawing. Continued increases to mean annual air temperature consistent with global climate change predictions will lead to permafrost warming and loss in some areas.
Some sites underlain by permafrost exhibited very little change evident in the photo pairs, whereas other sites exhibited dramatic changes called thermokarst. Thermokarst features form when the ground surface, previously supported by permafrost, collapses into itself due to the permafrost thawing. Sites with permafrost are fairly stable, meaning it takes a great deal of inertia for change to occur, because frozen ground is an impediment to many plant species. However, as soon as the permafrost is compromised, dramatic changes can occur quite rapidly, and can be devastating to a localized area.
As you browse the photo pairs, imagine what each site would look like if the underlying permafrost thawed. How would that affect the flora and fauna that utilize the site?