Mountain permafrost
At high elevations in mid-latitude mountains, permafrost is
widespread where the mean annual air temperature is below
–3°C. It often exists far below the altitudes to which glaciers ex-
tend, and even below the tree line in continental areas. Moun-
tain permafrost exists in different forms – in steep bedrock, in
p
e
rock glaciers, in debris deposited by glaciers or in vegetated
r
m
a
f
r
soil, and contains variable amounts of ice. Since topography
o
s
t
causes large variability in local climate, snow cover, and ground colder
and surface properties through the processes of erosion, trans-
port and deposition, mean annual ground temperatures in
mountain regions can vary by 5–8 °C over distances as small as
100 m (Figure 7.8). For this reason, the distribution and charac-
teristics of permafrost in mountain regions are very patchy.
Permafrost influences the evolution of mountain landscapes
and affects human infrastructure and safety. Permafrost warm-
warmer
ing or thaw affects the potential for natural hazards such as
rock falls, debris flows and secondary events triggered by them
Figure 7.8: Temperatures in a mountain range containing per-
and also affects the topography itself in steep terrain. As in
mafrost (blue colours bordered by the black line), ranging from
Arctic permafrost regions, construction in mountain perma-
colder (blue) to warmer (red). Steep terrain and strong variability
frost regions requires special precautions and warming perma-
in surface temperatures are typical of mountain permafrost. The
frost poses problems to infrastructure. Mountain permafrost
cross section in the foreground shows the complex distribution
also contains valuable information on climate change. The
of subsurface temperatures characteristic of mountains, with the
presence of permafrost, in an actively moving rock glacier for
isotherms (lines linking points of equal temperature) nearly verti-
example, indicates a relatively cold climate, therefore inactive
cal in the ridge of the mountain. In the background, the colours
or fossil rock glaciers point to past colder climates. Measure-
on the mountain surface illustrate the strong variability in ground
ments of permafrost temperature, as well as providing infor-
temperatures caused by differences in elevation, exposure to the
mation on present-day permafrost stability, offer data on past
sun, snow cover and ground properties. In the far background,
climate changes.
one can only guess at this complex pattern of permafrost distri-
bution because permafrost is invisible at the ground surface.
Source: S. Gruber, photo from Christine Rothenbühler
Mountain permafrost contains large quantities of stored km
3
while the estimate of ground ice volume is about
fresh water in the form of ice. Mountain permafrost 280 km
3
for one area of the Tien Shan Mountains
80,81
.
within debris deposited by glaciers, or in rock glaciers Considering the continued glacier recession in Central
and other coarse blocky material has especially high ice Asia (see Chapter 6B), the melt waters from permafrost
content (up to 80 per cent of the total volume). The total could become an increasingly important source of fresh
volume of surface ice has been reported at about 462 water in this region in the near future.
194 GLOBAL OUTLOOK FOR ICE AND SNOW