page_title: Permafrost
section_title: Massive ground ice
hierarchical_section_title: Permafrost / Manifestations / Massive ground ice
caption_attribution_description: English: Several types of massive ground ice, including ice wedges and intrasedimental ice, observable within the cliff wall of a retrogressive thaw slump located on the southern coast of Herschel Island. This exposure has a headwall that measures in excess of 22 m high and is over 1.3 km long. This cliff exposure has been increasing in size on a yearly basis since it was first measured in 1950 from air photographs.
context_page_description: Permafrost is ground that continuously remains frozen for two or more years, located on land or under the ocean. Permafrost does not have to be the first layer that is on the ground. It can be an inch to over miles deep into the Earth's surface. Some of the most common permafrost locations are located in the Northern Hemisphere. Almost a quarter of the Northern Hemisphere is underlain by permafrost, including 85% of Alaska, Greenland, Canada and Siberia. It can also be located in the Southern Hemisphere, just on mountain tops. Permafrost frequently occurs in ground ice, but it also can be presented in non-porous bedrock. Permafrost is formed from ice holding all different sorts of soil, sand, and rock combination together.
context_section_description: When the ice content of a permafrost exceeds 250 percent (ice to dry soil by mass) it is classified as massive ice. Massive ice bodies can range in composition, in every conceivable gradation from icy mud to pure ice. Massive icy beds have a minimum thickness of at least 2 m and a short diameter of at least 10 m. First recorded North American observations were by European scientists at Canning River, Alaska in 1919. Russian literature provides an earlier date of 1735 and 1739 during the Great North Expedition by P. Lassinius and Kh. P. Laptev, respectively. Two categories of massive ground ice are buried surface ice and intrasedimental ice (also called constitutional ice).
  Buried surface ice may derive from snow, frozen lake or sea ice, aufeis (stranded river ice) and—probably the most prevalent—buried glacial ice.
  Intrasedimental ice forms by in-place freezing of subterranean waters and is dominated by segregational ice which results from the crystallizational differentiation taking place during the freezing of wet sediments, accompanied by water migrating to the freezing front.
  Intrasedimental or constitutional ice has been widely observed and studied across Canada and also includes intrusive and injection ice.
  Additionally, ice wedges—a separate type of ground ice—produce recognizable patterned ground or tundra polygons. Ice wedges form in a pre-existing geological substrate and were first described in 1919.
caption: Several types of massive ground ice, including ice wedges and intrasedimental ice within the cliff wall of a retrogressive thaw slump located on the southern coast of Herschel Island within an approximately 22-metre (72 ft) by 1,300-metre (4,300 ft) headwall.
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