Geology Reference
In-Depth Information
Figure 7.1.
Classifi cation of ground ice based upon the water source and the principal transfer
processes at the time of freezing (modifi ed from Mackay, 1972b), together with ice descriptions
according to Pihlainen and Johnston (1963).
viewpoint because their occurrence gives rise to landforms such as ice-wedge polygons,
frost mounds, and ice-cored topography. In addition, pore ice and segregated ice not only
determine the amount of frost heave (see Chapter 4) but are also major determinants of
cryotextures and cryostructures (see below) and are essential elements in the thermokarst
process (see Chapter 8).
These four major types of ground ice and their characteristics require brief
description.
7.2.1. Pore Ice
Pore ice, sometimes termed interstitial or “cement” ice, is the bonding cement that holds
soil grains together. It is ubiquitous wherever moisture is present within permafrost and
occupies, in varying amounts, voids in the material concerned. It is widespread in near-
surface permafrost and in the active layer. The distinction between pore and segregated
ice relates to the water content of the soil. This is best determined by thawing the soil and
noting the presence or absence of excess ice or supernatant water. If supernatant water is
present, this indicates the frozen soil was supersaturated and segregated ice was present.
Pore ice has been discussed earlier in Chapter 4. In the Russian literature, pore ice give
rise to what are termed “massive” cryotextures (see below).
