Page 309 - Fundamentals of Geomorphology

292 PROCESS AND FORM

hectares of land. The increasing amount of land given
over to roads and buildings, together with the associated
disturbed land, has driven a fairly constant or increasing
a
() Free-face and
debris slope profile reindeerpopulationontoprogressivelysmallerpatchesof
pasture. In consequence, the patches have suffered exces-
sive grazing and trampling of lichens, bryophytes, and
shrubs. In many areas, sandy soils have been deflated.
The human- and reindeer-induced disturbance may eas-
ily initiate thermokarst formation and aeolian erosion,
which would lead to significant further losses of pasture.
Thermokarst is less likely to develop in the High
() Rectilinear debris-mantled
b
(Richter) slope Arctic, owing to the lower permafrost temperatures and
the generally lower ice content. Nonetheless, gully ero-
sion can be a serious problem in places lacking a peat
cover. For instance, snow piled up when clear areas for
airstrips and camps are ploughed melts in the spring.
The meltwater runs along minor ruts caused by vehicles.
In a few years, these minor ruts may be eroded into
sizeable gullies. A trickle of water may become a potent
erosive force that transforms the tundra landscape into
() Smooth convexo-concave a slurry of mud and eroding peat. Restoration work is
c
debris-mantled slopes difficult because gravel is in short supply and a loss of
soil volume occurs during the summer melt. In any case,
gravel roads, although they will prevent permafrost melt
and subsidence if they are thick enough, have deleteri-
ous side-effects. For instance, culverts designed to take
d
() Stepped profiles water under the roads may fill with gravel or with ice
in the winter. In three sites within the Prudhoe Bay Oil
Field, studied from 1968 to 1983, blocked drainage-ways
have led to 9 per cent of the mapped area being flooded
and 1 per cent of the area being thermokarst (Walker
et al. 1987). Had not the collecting systems, the camps,
() Pediment-like forms
e
and the pipeline corridors been built in an environmen-
tally acceptable manner, the flooding and conversion to
thermokarst might have been far greater. Water running
parallel to the roads and increased flow from the culverts
Figure 11.6 Types of periglacial slopes. (a) Cliff may lead to combined thermal and hydraulic erosion and
above a debris slope. (b) Rectilinear, debris-mantled or the production of thermokarst.
Richter slope. (c) Smooth concavo-convex profile Global warming during the twenty-first century is
with frost-shattered and solifluction debris. bound to have a large impact on permafrost land-
(d) Stepped profiles: cryoplanation or altiplanation scapes, and no effectual countermeasures are available
terraces. (e) Pediment-like forms, or cryopediments. (Lunardini1996).Muchofthediscontinuouspermafrost
Source: Adapted from French (1996, 171)
in Alaska is now extremely warm, usually within 1–2 C
◦
of thawing. Ice at this temperature is highly suscepti-
ble to thermal degradation, and any additional warming