Geology Reference
In-Depth Information
locations in the Mackenzie Mountains and southern Yukon Territory, Canada (Coultish
and Lewkowicz, 2003; Kershaw and Gill, 1979; Lewkowicz and Coultish, 2004). Because
high hydraulic potentials must exist in such hilly topography, the possibility exists that
ice injection, rather than ice segregation, is the primary cause of uplift.
6.5.6. Hydrolaccoliths and Other Frost-Induced Mounds
A feature of many tundra landscapes is the presence of small mounds, many with either
ice cores or ice lenses within them (Figure 6.17). These mounds are not regarded as pingos,
mainly on account of their size and their location primarily within the active layer. They
are also not usually regarded as a form of patterned ground since they are larger than the
earth hummocks or non-sorted circles normally associated with patterned ground. Many
function as owl perches and stand out as relatively dry sites. Their peaty soil frequently
promotes the development of ice lenses immediately beneath the vegetation mat.
The variety of features suggests that they are not all of the same origin. In the Russian
literature, the term “bugor” has been used to describe these small, gently-rising, and oval-
shaped mounds (Dostovalov and Kudryavtsev, 1967). The North American literature
(Sigafoos, 1951; Sharp, 1942a; Bird, 1967, p. 203; Porsild, 1955; French, 1971a; Washburn,
1983b) describes low circular mounds, rarely exceeding 2 m in height, and usually between
15 m and 50 m in diameter. The origin of these features is not clear. Some are probably
the result of localized ice segregation that has occurred in response to subtle thermal dif-
ferences in soil and vegetation cover.
6.6. ACTIVE-LAYER PHENOMENA
The active layer (see Chapter 5) gives rise to a number of small-scale features of the per-
mafrost landscape. These include disrupted bedrock and soil, and various patterned-
ground phenomena. These are described below.
Figure 6.17.
Small hydrolaccolith associated with poorly-drained low-centered ice-wedge poly-
gons, Masik Valley, southern Banks Island, Canada. The mound consists of a body of pure ice
immediately beneath the organic mat. The raised rims of the polygons create a closed system during
annual freezing.
