PERIGLACIAL LANDSCAPES - Fundamentals of Geomorphology

Geology Reference

In-Depth Information

pipe in the ground for most of the route, but as the

oil is carried at 70-80 ◦ C this would have melted the

permafrost and the resulting soil flow would have

damaged the pipe. In the event, about half of the

pipe was mounted on elevated beams held up by

120,000 vertical support members (VSMs) that were

frozen firmly into the permafrost using special heat-

radiating thermal devices to prevent their moving.

This system allows the heat from the pipe to be dis-

sipated into the air, so minimizing its impact on the

permafrost.

Few roads and railways have been built in permafrost

regions. Most roads are unpaved. Summer thawing,

with concomitant loss of load-bearing strength in fine-

grained sediments, and winter frost-heaving call for

the constant grading of roads to maintain a surface

smooth enough for driving. Paved roads tend to

become rough very quickly, most of them requiring

resurfacing every 3 to 5 years. Railways are difficult to

build and expensive to keep up in permafrost regions.

The Trans-Siberian Railway, and some Canadian rail-

ways in the north of the country (e.g. the Hudson

Bay railway), cross areas where the ground ice is thick.

At these sites, year-round, costly maintenance pro-

grammes are needed to combat the effects of summer

thawing and winter frost-heaving and keep the track

level. The Hudson Bay railway has been operating for

over 60 years. For all that time, it has faced problems

of thaw settlement along the railway embankment and

the destruction of bridge decks by frost heave. Heat

pipes help to minimize thaw subsidence but they are

very expensive.

during the current century will result in the formation of

new thermokarst (Osterkamp et al . 2000). In the Yamal

Peninsula, a slight warming of climate, even without the

human impacts on the landscape, would produce massive

thermokarst erosion (Forbes 1999).

ground is a geometrical arrangement of circles, polygons,

nets, steps, and stripes. Periglacial slopes include cry-

oplanation terraces. Human activities in periglacial envi-

ronments and global warming are leading to permafrost

degradation and the formation of thermokarst.

SUMMARY

ESSAY QUESTIONS

Periglacial landscapes experience intense frosts during

winter and snow-free ground during the summer. They

are underlain by either continuous or patchy permafrost

(permanently frozen ground), which at present lies

beneath about 22 per cent of the land surface. Several

geomorphic processes operate in periglacial environ-

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

also be very effective land-formers in periglacial envi-

ronments. Periglacial landforms, some of them bizarre,

include ice wedges, a range of frost mounds (pingos,

palsa, peat plateaux, string bogs, frost blisters, icing

mounds and icing blisters), thermokarst and oriented

lakes, patterned ground, and distinctive slopes. Patterned

1 How distinctive are periglacial

landforms?

2 How does patterned ground form?

3 Examine the problems of living in

periglacial environments.