Some aspects on applied geomorphology in periglacial regions
215
is lower. Cuttings into these deposits may easily affect the stability of the accumulation of
frost-shattered clasts. In some mountain areas like the Peruvian Andes, some roads require
the daily removal of clasts (Gerrard, 1990).
There is a very large occurrence of large rock avalanches in mountain regions involving
the displacement of several millions of cubic metres at velocities higher than 100 km/h.
The rock avalanche triggered in Mount Rainier in Washington by the 1964 earthquake
travelled 7 km with a height difference of 2000 m, and the Sherman Glacier rock
avalanche covered 8.25 km 2 in Alaska. The physical damage caused by these rock
avalanches was limited. The translational rockslide of Mayunmarca village, in the central
Peruvian Andes that occurred in April 1974, however, killed 451 people. This mass
movement was caused by undercutting of a slope by the River Mantaro (Voight and
Pariseau, 1978). The historical and geological record demonstrates that mass movements
commonly develop several times in a particular location showing a recurrent character.
Inzing village and several sectors of the Voralberg in the Austrian Alps have suffered from
recurrent and catastrophic mass movements during the last centuries (Gerrard, 1990).
Despite the numerous protection measures, on 26 July 1966, Inzing village was affected by
a channelled debris avalanche that travelled at 100 km/h killing three people and burying
4 km of road and 500 m of railway. A great part of the protection structures were
destroyed.
In some circumstances active rock glaciers may constitute a geomorphological hazard.
The damage caused by their activity results from the downslope flow of the frozen
material, the subsidence and generation of depressions (several metres or tens of metres in
size) caused by the thawing of the underlying ice and the eluviation of fine particles, and
the fall of surficial blocks related to the higher speed of the upper bouldery layer (this
process may reach rates of 1 block per minute) (Giardino and Vick, 1987). These sites
should be avoided for the installation of structures like poles or towers for electric lines or
ski lifts. In the Rocky Mountains of Colorado, USA, communication routes and pipelines
that cross active rock glaciers need periodic maintenance work and in some cases the
courses have had to be modified. Tunnels excavated in rock glaciers as in the case of
Mount Mestas, Rocky Mountains, Colorado, are affected by deformations and collapses
due to the hydrostatic pressures related to thawing of the ice (Giardino, 1983).
The development of slides affecting the active layer is a very common process in
permafrost areas during the melting season. These mass movements generally have a
shallow failure surface and may reach high speeds (Harris, 1986). In riverbanks, the
generation of thermoerosion niches allows the formation of falls, topples, and debris flows
with speeds reaching up to 10 m/s (Harris, 1981). In addition, the presence of periglacial
deposits with low shear strength is relatively common in mid-latitude areas subjected to
periglacial conditions during the Pleistocene period. The fulfilment of construction works
in these unstable materials may pose numerous problems (Derbyshire, 1977).
4. Engineering problems in permafrost areas
The thermal equilibrium of the permafrost is easily disturbed by human activities causing
its degradation or expansion. The reduction or removal of the vegetation cover favours
the degradation of the permafrost. In recent times the construction of buildings, roads,
215
is lower. Cuttings into these deposits may easily affect the stability of the accumulation of
frost-shattered clasts. In some mountain areas like the Peruvian Andes, some roads require
the daily removal of clasts (Gerrard, 1990).
There is a very large occurrence of large rock avalanches in mountain regions involving
the displacement of several millions of cubic metres at velocities higher than 100 km/h.
The rock avalanche triggered in Mount Rainier in Washington by the 1964 earthquake
travelled 7 km with a height difference of 2000 m, and the Sherman Glacier rock
avalanche covered 8.25 km 2 in Alaska. The physical damage caused by these rock
avalanches was limited. The translational rockslide of Mayunmarca village, in the central
Peruvian Andes that occurred in April 1974, however, killed 451 people. This mass
movement was caused by undercutting of a slope by the River Mantaro (Voight and
Pariseau, 1978). The historical and geological record demonstrates that mass movements
commonly develop several times in a particular location showing a recurrent character.
Inzing village and several sectors of the Voralberg in the Austrian Alps have suffered from
recurrent and catastrophic mass movements during the last centuries (Gerrard, 1990).
Despite the numerous protection measures, on 26 July 1966, Inzing village was affected by
a channelled debris avalanche that travelled at 100 km/h killing three people and burying
4 km of road and 500 m of railway. A great part of the protection structures were
destroyed.
In some circumstances active rock glaciers may constitute a geomorphological hazard.
The damage caused by their activity results from the downslope flow of the frozen
material, the subsidence and generation of depressions (several metres or tens of metres in
size) caused by the thawing of the underlying ice and the eluviation of fine particles, and
the fall of surficial blocks related to the higher speed of the upper bouldery layer (this
process may reach rates of 1 block per minute) (Giardino and Vick, 1987). These sites
should be avoided for the installation of structures like poles or towers for electric lines or
ski lifts. In the Rocky Mountains of Colorado, USA, communication routes and pipelines
that cross active rock glaciers need periodic maintenance work and in some cases the
courses have had to be modified. Tunnels excavated in rock glaciers as in the case of
Mount Mestas, Rocky Mountains, Colorado, are affected by deformations and collapses
due to the hydrostatic pressures related to thawing of the ice (Giardino, 1983).
The development of slides affecting the active layer is a very common process in
permafrost areas during the melting season. These mass movements generally have a
shallow failure surface and may reach high speeds (Harris, 1986). In riverbanks, the
generation of thermoerosion niches allows the formation of falls, topples, and debris flows
with speeds reaching up to 10 m/s (Harris, 1981). In addition, the presence of periglacial
deposits with low shear strength is relatively common in mid-latitude areas subjected to
periglacial conditions during the Pleistocene period. The fulfilment of construction works
in these unstable materials may pose numerous problems (Derbyshire, 1977).
4. Engineering problems in permafrost areas
The thermal equilibrium of the permafrost is easily disturbed by human activities causing
its degradation or expansion. The reduction or removal of the vegetation cover favours
the degradation of the permafrost. In recent times the construction of buildings, roads,