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How does pore ice form in permafrost?
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permafrost
Distribution of permafrost in the Northern Hemisphere.
Pore ice forms in permafrost when water already present within the pore spaces of the ground freezes in situ.1
Unlike other forms of ground ice that grow by drawing in additional moisture, pore ice does not involve the addition of water to the soil. Consequently, the ground contains no more water in its solid state than it could originally hold in its liquid state. This type of ice serves to fill or partially fill the existing voids within the soil matrix.1