Permafrost
Pingo near Tuktoyaktuk, Northwest Territories. Photo: Greg Brooks,
NRCan, Geological Survey of Canada
Inset left: Repeated seasonal frost heaving forces large rocks to the surface,
where they stay because of fine particles filling in the resulting spaces. Over
years of freeze/thaw, the large rocks are pushed to the sides forming sorted
circles. Photo: John Meikle, Government of Yukon
Inset right: Collapsed frost circle, Tombstone Mountains, Yukon.
Photo: John Meikle, Government of Yukon
Permafrost underlies the formation of Beringia.
Whitehorse lies in an area of discontinuous permafrost. Permafrost is ground that remains permanently frozen. In most cases, it underlies a layer of ground that freezes and thaws seasonally. Mammoth and bison carcasses, intact with hair, skin and organs have been preserved in Beringian permafrost that dates back tens of thousands of years, having survived periods both warmer and colder than today.
Labrador Tea. Photo: John Meikle, Government of Yukon
Inset: Fields of cotton-grass are common in tundra areas underlain by permafrost,
Dempster Highway, Yukon. Photo: Cathie Archbould
Permafrost defines where plants will survive.
Permafrost has shaped and defined much of the Beringian landscape of the past and present. In regions of permafrost, plant roots can only reach down as far as the permanently frozen layer, limiting their growth. Because water cannot drain through permafrost, these areas are also too wet for many types of plants. Cotton grass and Labrador tea, that survived the last glacial age in Beringia, are adapted to these conditions. Permafrost also shapes the land surface into large and small formations such as pingos, polygons and the sorted circles in front of you.
Treeline and permaforst in North America. Note how the treeline roughly follows
the line of continuous permafrost.
Melting permafrost collapses the ground.
On the arctic coastal plain of Alaska, surface temperatures have risen by about 2°C (3.6°F) over the past few decades. A rise in surface temperature percolates down through the permafrost over a period of years. Increased permafrost melt will cause the overlying ground to collapse, forming thermokarst lakes and ponds, and thaw slumps.
When ice-rich permafrost melts, it causes the land surface to collapse, creating
thermokarst ponds and causing trees to tilt forming "drunken forests."
Photo: Lynda Dredge, NRCan, Geological Survey of Canada
If the dead plants frozen in permafrost thaw and decompose, as much as one seventh of the earth's carbon will be released which will greatly increase global warming.