Permafrost thaw Versus melt
Ground can consist of many substrate materials, including bedrock, sediment, organic matter, water or ice. Frozen ground is that which is below the freezing point of water, whether or not water is present in the substrate. Ground ice is not always present, as may be the case with nonporous bedrock, but it frequently occurs and may be present in amounts exceeding the potential hydraulic saturation of the thawed substrate. Permafrost is ground that remains frozen for two or more years. Since frozen soil, including permafrost, comprises a large percentage of substrate materials other than ice, it thaws rather than melts even as any ice content melts. An analogy is when a freezer door is left open, although the ice in the freezer may change phase to a liquid, the food solids will not experience a phase change. In aggregate, the food thaws but does not melt. Melting implies the phase change of all solids to liquid.
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