ice in the earth’s crust of any origin or mode of occurrence. In terms of time of formation, a distinction is made between modern and fossil ice, and in terms of origin, primary (syngenetic), secondary (epigenetic), and buried ice are distinguished.
Primary subsurface ice is formed during the freezing of accumulating deposits that are loose before freezing. It constitutes a predominant part of subsurface ice and is found primarily in the form of contact, interstitial, and film basal ice cement and, more rarely, in the form of large lenses and bands, known as segregation or injection ice. The formation of the last two types of subsurface ice causes frost heaving on the earth’s surface.
Secondary subsurface ice is the product of the crystallization of water and water vapor in cracks (vein ice) and pores and cavities (honeycomb ice) of solidly frozen rock or already formed rock that is freezing. As a result of the annually recurring filling of frost cracks with ice, reveined ice is formed, occurring in the form of a tetragonal lattice of stratified vertical ice veins. If new sediments accumulate at the same time as ice veins form, the ice veins will gradually grow as the level rises. Such (syngenetic) ice veins grow during the accumulation of freezing sediments to a width of up to 8 m and a height of up to 40–80 m, constituting up to 70 percent of the area of the coastal plains of northern Siberia and Alaska.
Epigenetic recurring ice veins that penetrate frozen loose sediments do not extend to a depth of more than several meters.
Buried ice is formed initially on the earth surface (for example, snowfields, icing, and sea, lake, and river ice) and is later buried beneath sedimentary rock. The largest masses of buried ice are the “dead ice” of glaciers. All buried ice taken together constitutes the smallest portion of subsurface ice.
REFERENCESShumskii, P. A. Osnovy strukturnogo ledovedeniia. Moscow, 1955.
Osnovy geokriologii (merzlotovedeniia), part 1. Moscow, 1959.
Dostovalov, B. N., and V. A. Kudriavtsev. Obshchee merzlotovedenie. Moscow, 1967.