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The maximum frost depth observed in the contiguous United States ranges from 0 to 8 feet (2.4 m). [1] Below that depth, the temperature varies, but is always above 0 °C (32 °F). Alternatively, in Arctic and Antarctic locations the freezing depth is so deep that it becomes year-round permafrost, and the term "thaw depth" is used
The depth of frost crystals varies depending on the amount of time they have been accumulating, and the concentration of the water vapor . Frost crystals may be invisible (black), clear (translucent), or, if a mass of frost crystals scatters light in all directions, the coating of frost appears white.
The term frost front refers to the varying position of the thaw line during the periods of freezing/thawing. The knowledge of the thaw depth is important for the two major reasons: its influence on the ecology and on construction ( buildings , pipelines , roads , etc.).
Photograph taken 21 March 2010 in Norwich, Vermont. Frost heaving (or a frost heave) is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil (the freezing front or freezing boundary).
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 ...
Ground frost refers to the various coverings of ice produced by the direct deposition of water vapor on objects and trees, whose surfaces have a temperature below the freezing point of water (0 °C, 32 °F).
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The red dotted-to-solid line depicts the average temperature profile with depth of soil in a permafrost region. The trumpet-shaped lines at the top show seasonal maximum and minimum temperatures in the "active layer", which commences at the depth where the maximum annual temperature intersects 0 °C. The active layer is seasonally frozen.