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What is permafrost?
Permafrost is ground material that remains at or below 0°C or 32°F for two or more consecutive years. Native vegetation acts as insulation against warm summer air temperatures.
Clearing land removes the insulating protection, exposing permafrost to thaw. Additionally, many agricultural practices in Alaska artificially warm the soil, such as using mulches or growing in high tunnels. These techniques can also contribute to unintended permafrost thaw.
Clearing land removes the insulating protection, exposing permafrost to thaw. Additionally, many agricultural practices in Alaska artificially warm the soil, such as using mulches or growing in high tunnels. These techniques can also contribute to unintended permafrost thaw.
Frozen
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Thawed
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Ice-rich permafrost is thaw-unstable, as it causes land to sink (called thaw subsidence), often resulting in pond formation and leaning trees creating “drunken forests.”
Ice-poor permafrost is thaw-stable as it does not cause subsidence when it thaws.
Notice how an ice-rich and ice-poor core look similar when the permafrost is frozen, but the results from thawing are drastically different.
Click here to watch a time-lapse of this thawing experiment.
Ice-poor permafrost is thaw-stable as it does not cause subsidence when it thaws.
Notice how an ice-rich and ice-poor core look similar when the permafrost is frozen, but the results from thawing are drastically different.
Click here to watch a time-lapse of this thawing experiment.
This field at the Fairbanks Experiment Farm was level in 1932. Due to thawing ice-rich permafrost, the land had collapsed by 1939.
Image from the Agricultural Experiment Station Photograph Collection. Identifier: UAF-1968-4-1346.
Image from the Agricultural Experiment Station Photograph Collection. Identifier: UAF-1968-4-1346.
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