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Permafrost temperature profile. Permafrost occupies the middle zone, with the active layer above it, while geothermal activity keeps the lowest layer
Permafrost temperature profile. Permafrost occupies the middle zone, with the active layer above it, while geothermal activity keeps the lowest layer above freezing. The vertical 0 °C or 32 °F line denotes the average annual temperature that is crucial for the upper and lower limit of the permafrost zone, while the red lines represent seasonal temperature changes and seasonal temperature extremes. Solid curved lines at the top show seasonal maximum and minimum temperatures in the active layer, while the red dotted-to-solid line depicts the average temperature profile with depth of soil in a permafrost region.
Excavating ice-rich permafrost with a jackhammer in Alaska.
Excavating ice-rich permafrost with a jackhammer in Alaska.
Changes in subsea permafrost extent and structure between the Last Glacial Maximum and now.
Changes in subsea permafrost extent and structure between the Last Glacial Maximum and now.
A group of palsas, as seen from above, formed by the growth of ice lenses.
A group of palsas, as seen from above, formed by the growth of ice lenses.
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A patch of grass showing three zones. crystalline frost in the below-freezing shade (blue, lower right) frost in the warming but still below freezing
A patch of grass showing three zones. crystalline frost in the below-freezing shade (blue, lower right) frost in the warming but still below freezing strip most recently exposed to sunlight (white, center) frost-free region: here, the previous frost has melted from a more prolonged exposure to sunlight (green, upper left.)
A spider web covered in air hoar frost
A spider web covered in air hoar frost
Hoar frost on the snow
Hoar frost on the snow
Depth hoar, imaged with optical (left) and scanning electron (right) microscopy
Depth hoar, imaged with optical (left) and scanning electron (right) microscopy