Page 311 - Fundamentals of Geomorphology

294 PROCESS AND FORM

pipe in the ground for most of the route, but as the smooth enough for driving. Paved roads tend to
oil is carried at 70–80 C this would have melted the become rough very quickly, most of them requiring
◦
permafrost and the resulting soil flow would have resurfacing every 3 to 5 years. Railways are difficult to
damaged the pipe. In the event, about half of the build and expensive to keep up in permafrost regions.
pipe was mounted on elevated beams held up by The Trans-Siberian Railway, and some Canadian rail-
120,000 vertical support members (VSMs) that were ways in the north of the country (e.g. the Hudson
frozen firmly into the permafrost using special heat- Bay railway), cross areas where the ground ice is thick.
radiating thermal devices to prevent their moving. At these sites, year-round, costly maintenance pro-
This system allows the heat from the pipe to be dis- grammes are needed to combat the effects of summer
sipated into the air, so minimizing its impact on the thawing and winter frost-heaving and keep the track
permafrost. level. The Hudson Bay railway has been operating for
Few roads and railways have been built in permafrost over 60 years. For all that time, it has faced problems
regions. Most roads are unpaved. Summer thawing, of thaw settlement along the railway embankment and
with concomitant loss of load-bearing strength in fine- the destruction of bridge decks by frost heave. Heat
grained sediments, and winter frost-heaving call for pipes help to minimize thaw subsidence but they are
the constant grading of roads to maintain a surface very expensive.

during the current century will result in the formation of ground is a geometrical arrangement of circles, polygons,
new thermokarst (Osterkamp et al. 2000). In the Yamal nets, steps, and stripes. Periglacial slopes include cry-
Peninsula, a slight warming of climate, even without the oplanation terraces. Human activities in periglacial envi-
human impacts on the landscape, would produce massive ronments and global warming are leading to permafrost
thermokarst erosion (Forbes 1999). degradation and the formation of thermokarst.

SUMMARY
ESSAY QUESTIONS
Periglacial landscapes experience intense frosts during 1 How distinctive are periglacial
winter and snow-free ground during the summer. They landforms?
are underlain by either continuous or patchy permafrost
(permanently frozen ground), which at present lies 2 How does patterned ground form?
beneath about 22 per cent of the land surface. Several 3 Examine the problems of living in
geomorphic processes operate in periglacial environ- periglacial environments.
ments. Frost action is a key process. It causes weathering,
heaving and thrusting, mass displacement, and cracking.
Frost creep and gelifluction dominate mass movements.
Nivation combines several processes to form hollows
under snow patches. Fluvial and aeolian action may FURTHER READING
also be very effective land-formers in periglacial envi-
ronments. Periglacial landforms, some of them bizarre, Ballantyne, C. K. and Harris, C. (1994) The Periglacia-
include ice wedges, a range of frost mounds (pingos, tion of Great Britain. Cambridge: Cambridge University
palsa, peat plateaux, string bogs, frost blisters, icing Press.
mounds and icing blisters), thermokarst and oriented A very good book that includes an introduction to the
lakes, patterned ground, and distinctive slopes. Patterned idea of periglaciation.