frozen ground or permafrost

hydrochemical talik

a layer or body of cryotic (but unfrozen) ground in a permafrost area, maintained by moving mineralized groundwater.

hydraulic thawing

artificial thawing (and removal) of frozen ground by the use of a stream or jet of water under high pressure.

hydraulic diffusivity

the ratio of the hydraulic conductivity and the storage capacity of a groundwater aquifer.

hydraulic conductivity

the volume of fluid passing through a unit cross section in unit time under the action of a unit hydraulic potential gradient.

hydration shattering

a form of weathering that affects all rocks; water freezes in pores and cracks, which leads to an increase in specific volume (vol/unit mass) of the water, producing stress that is greater than the tensile strength of all common rocks; ultimately leads to shattering and fracturing of the rocks.

hummock

(1) [sea ice] a smooth hill of ice that forms on the sea ice surface from eroding ridges, particularly during the summer melt; the formation of hummocks is similar to young mountain peaks with steep slopes that erode into smooth, rolling hills. (2) [frozen ground] Small lumps of soil pushed up by frost action, often found in uniformly spaced in large groups. Hummocks can form in areas of permafrost or seasonally frozen ground, and are one of the most common surface features of the Arctic.
Hummocks make the sea ice surface appear as rolling hills. (Photo courtesy of Ted Maksym, United States Naval Academy.)

high-center polygon

an ice-wedge polygon in which melting of the surrounding ice wedges has left the central area in a relatively elevated position.

heaving pressure

upward pressure developed during freezing of the ground.

heat capacity

the amount of heat required to raise the temperature of a unit mass of a substance by one degree.

hard frozen ground

frozen ground (soil or rock) which is firmly cemented by ice.

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