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with lower soil strengths and lower adhesion forces, thus
giving ground instability and increased slope failure.
Several Arctic countries are mapping the sensitivity
of permafrost to climate warming. Canadian research
combines two indices: (1) the thermal response to
warming, or change in ground temperature, and (2) the
physical response to warming, or relative impact of thaw.
The physical response is considered to be more important
than the thermal response, especially in areas of high
massive-ice contents (Smith and Burgess 2004). One of the
difficulties of prediction is because permafrost is affected
by vegetation, soil and snow conditions in addition to
atmospheric temperature. Luthin and Guymon (1974)
proposed a buffer-layer model with the vegetation canopy,
snow cover, surface organic material and water acting as
buffers between the atmosphere and the ground (
Figure
normal within small areas of uniform climate, and
therefore large differences in the rates of permafrost
degradation will be typical too.
Climate warming may lead to an increase in the
frequency of wildfires in tundra regions. In peaty areas the
burning of the dry surface peat would lead to permafrost
degradation as the loss of insulation from the peat allowed
summer heat to penetrate into the ground. Also the
burning of trees in the subarctic zone causes soil instability
and an increase in active-layer detachment slides results
Because permafrost provides an impermeable layer
that restricts soil drainage and produces ponds and
wetlands, any loss of permafrost will improve drainage
and may lead to a loss of wetland, resulting in a change
of vegetation patterns and the loss of breeding habitats for
wildlife. Rivers normally have a quick response to
snowmelt and rainfall where permafrost is present. As
permafrost melts, subsurface flow will become more
important and stream flow more uniform, with winter
flow becoming more prominent. Deeper active layers with
more unfrozen water may increase frost heave, giving
more
hummock features
, with associated engineering
problems.
Icings
may increase, giving more road hazards.
The sensitivity of ground ice to change, whether by natural
causes or by human impact, is typified in
Plate 15.25
.
Taken in 1998 at the construction site of the new Ekati
diamond mine near Lac de Gras, North West Territories,
Canada, engineering work on an esker has revealed a bed
of massive ice. Now it is exposed, thawing and ground
subsidence will inevitably follow.
CONCLUSION
Glaciation and global icehouse conditions are a recurring
Earth surface state and not a climatic abnormality or
'accident'. It is not merely a by-product of climatic change
but can also instigate or mitigate it through ice
sheet-ocean-atmosphere coupling. Polar ice sheet and
Alpine glacier growth is strongly influenced by tectonic
activity as well as Milankovich mechanisms (see
Chapter
9).
Glaciers, in turn, drive other forms of glaciotectonic
coupling through the rapid alteration of crustal loading
by ice sheet growth and decay, glacial erosion and
sediment transfers, and glacio-eustasy. All this creates
glacier and permafrost material and geomorphic systems
which are not solely determined by climate but interact
with climatic and tectonic processes to set their own rules.
The environmental influence of glaciers and perma-
frost extends well beyond their current geographical
distribution. The greater part of hominid evolution has
occurred during the Quaternary Ice Age and continues
to be profoundly influenced by it. Dramatic human
population explosion and almost all our technological
innovation have occurred in just 10 ka of the current
(Flandrian) interglacial cycle. We need to be as responsive
to Earth's icehouse mode as to its greenhouse mode.
The atmosphere
Vegetation canopy
Buffer
layer
Snow cover
Organic layer
Mineral soil
Geothermal regime
boundary layer interactions affecting ground temperature in
permafrost zones.
Source: After Luthin and Guymon (1974)
