- seasonal in temperate climates
- permanent in cold environments
- ground ice is present in a variety of
forms (Mackay, 1972, World of underground ice, Annals of the
Association of American Geographers, vol. 62), but there are two main
types:
- pore (interstitial) ice: freezing of
the water in the pore spaces in soil and rock
- segregated ice: bodies (lenses,
wedges, seams, etc.) of pure ice that forms and grow as
soil water is diffused towards the lower vapour pressure at the
freezing plane
hydrologic significance of ground ice
- permafrost
- permanently frozen ground usually
contains ice
- thus the distribution of permanent
ground ice is linked to the distribution of permafrost
- this water can be stored as ice for
tens of thousands of years, i.e., much permafrost and
ground ice is relict from the colder climate of the late
Pleistocene
- seasonally thawed ground
- in the active layer, water trapped
above the permafrost table participates in the hydrological cycle
during a short spring and summer
- segregated ice
- develops by attracting water, and
thereby depleting the water content of surrounding sediments
- needle ice is a form of segregated
ice that forms on wet ground on cold nights, thereby desiccating
the soil surface
- lack of baseflow
- interflow and overland flow from a
saturated active layer tend to be the dominant source of runoff,
because groundwater is either frozen or trapped below permafrost
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