Geoscience Reference
In-Depth Information
There are signifi cant numbers of viable ancient microorganisms within permafrost.
They have been isolated in both polar regions from cores up to 400 m deep and ground
temperatures of −27 °C (Gilichinsky et al.
2008
). The age of the cells dates back to ~3
million year in the arctic and ~5 million year in Antarctica. They are the only life
forms known to have retained viability over geologic time.
4.2.4
Humans
Humans have played a major role in soil development over the past 100-150 years.
In the arctic, mining activities and extraction of petroleum products have impacted
soils. In the Antarctic there are some 72 scientifi c bases that have left a small but
detectable infl uence on the terrestrial and aquatic ecosystems. The management of
cryosols at all three “poles” is considered in Chap.
13
.
4.3
Patterned Ground
4.3.1
Patterned Ground Forms
Patterned ground is a general term for any ground surface exhibiting a discernibly
ordered, more or less symmetrical, morphological pattern of ground and, where
present, vegetation. Some patterned ground features are not confi ned to perma-
frost regions, but they are best developed in regions of present or past intensive
frost action.
A descriptive classifi cation of patterned ground includes sorted and poorly sorted
or unsorted circles, nets, polygons, steps, stripes, and solifl uction features. Several
of the sorted forms are illustrated in Fig.
4.5
. In permafrost regions, the most ubiq-
uitous macro-form is the ice-wedge polygon, a common micro-form is the unsorted
circle called frost boils, and earth hummocks (Fig.
4.6
). Patterned ground also
occurs in peat lands in the form of strangmoor and frost mounds (Fig.
4.6
). Detailed
discussions of patterned ground features are given in Washburn (
1956
,
1980
).
4.3.1.1
Ice-Wedge Polygons
Ice-wedge polygons are formed by thermal cracking of the underlying permafrost
during winter freezing. The cracks project upward to the surface. During thawing of
the active layer in spring, water fl ows down into the crack. The cracks gradually
build up horizontally, and horizontal compression produces upturned of the frozen
sediments by plastic deformation. Eventually the cracks may become several meters
