224
Climatic Geomorphology
problems are related to the freezing state of the rocks and minerals and with the ice content
of the minerals. In addition, the transport of the minerals is generally restricted to the
thawing season (Harris, 1986).
The exploitation of placer deposits requires the thawing of the detrital deposits previous
to mechanical treatment. The ground ice is thawed with water under pressure. In former
times hot water was used but this method was costly and of small efficiency. These
practices have a high cost and, therefore, are only applied to high-value ores like gold,
platinum, cassiterite, and wolframite. In Alaska, the main mined placer deposits are the
sandurs developed at the foot of the mountains by melt waters derived from the
Pleistocene glaciers (French et al., 1983).
In open-cast mines the mineral-beating rocks have a lower ice content than the placer
deposits. One of the most relevant problems is related to the stability of the excavation
fronts whose mechanical strength is reduced by the melting of the ground ice (Harris, 1986).
The extraction of the mineral and the accompanying rock is carried out with perforation and
explosive networks. Boreholes drilled with the use of water may have problems because it
may freeze. For this reason, dry holes are employed on some occasions. The continuous
melting in these excavations makes it necessary to drain the surficial water to facilitate the
works. Obviously, the profitability of these costly workings is highly dependent on the
variations of the mineral price.
The presence of permafrost affects the strength and stability of the country rock in
underground mine workings. The entrances to the galleries are highly unstable due to the
thawing of the permafrost and have a high rock-fall hazard (Linell and Lobacz, 1978).
Most of the mines in permafrost zones are ventilated with air at 5 to 10~ that causes the
thawing of the roofs and walls affecting to their stability. The melt waters generates a
continuous water flow that has to be extract with pumps (Harris, 1986). In some cases the
water may penetrate in a sudden manner into the mine galleries causing floods capable of
causing tragic effects.
4.5. Other activities
Water is essential for the maintenance of settlements in periglacial regions. It is necessary
to have good quality drinkable water. Water for industrial use is commonly derived from
the treatment of waste waters (Harris, 1986). In these regions it is generally difficult to
obtain perennial water at low cost. Underground water may be found beneath or above the
permafrost or within the talik (French, 1996). The water obtained has to endure the whole
year and for this reason it is generally stored in deep reservoirs to mitigate the effect of the
thick ice layer that forms during the winter season.
A common problem faced in this region is also the disposal of waste waters and solid
wastes. These may pass on diseases and pollute the environment. Several methods are used
for their elimination (physical-chemical, biological, grinding, incineration, etc.) (Harris,
1986).
In some areas with continuous and discontinuous permafrost as in Yakutia (Siberia),
there is extensive grain agriculture. Here, the thawing caused largely by agricultural
practices produces thermokarst phenomena (Czudek and Demek, 1970b) and machinery
frequently sinks in thaw holes. Usually, the alas topography makes agricultural works
Climatic Geomorphology
problems are related to the freezing state of the rocks and minerals and with the ice content
of the minerals. In addition, the transport of the minerals is generally restricted to the
thawing season (Harris, 1986).
The exploitation of placer deposits requires the thawing of the detrital deposits previous
to mechanical treatment. The ground ice is thawed with water under pressure. In former
times hot water was used but this method was costly and of small efficiency. These
practices have a high cost and, therefore, are only applied to high-value ores like gold,
platinum, cassiterite, and wolframite. In Alaska, the main mined placer deposits are the
sandurs developed at the foot of the mountains by melt waters derived from the
Pleistocene glaciers (French et al., 1983).
In open-cast mines the mineral-beating rocks have a lower ice content than the placer
deposits. One of the most relevant problems is related to the stability of the excavation
fronts whose mechanical strength is reduced by the melting of the ground ice (Harris, 1986).
The extraction of the mineral and the accompanying rock is carried out with perforation and
explosive networks. Boreholes drilled with the use of water may have problems because it
may freeze. For this reason, dry holes are employed on some occasions. The continuous
melting in these excavations makes it necessary to drain the surficial water to facilitate the
works. Obviously, the profitability of these costly workings is highly dependent on the
variations of the mineral price.
The presence of permafrost affects the strength and stability of the country rock in
underground mine workings. The entrances to the galleries are highly unstable due to the
thawing of the permafrost and have a high rock-fall hazard (Linell and Lobacz, 1978).
Most of the mines in permafrost zones are ventilated with air at 5 to 10~ that causes the
thawing of the roofs and walls affecting to their stability. The melt waters generates a
continuous water flow that has to be extract with pumps (Harris, 1986). In some cases the
water may penetrate in a sudden manner into the mine galleries causing floods capable of
causing tragic effects.
4.5. Other activities
Water is essential for the maintenance of settlements in periglacial regions. It is necessary
to have good quality drinkable water. Water for industrial use is commonly derived from
the treatment of waste waters (Harris, 1986). In these regions it is generally difficult to
obtain perennial water at low cost. Underground water may be found beneath or above the
permafrost or within the talik (French, 1996). The water obtained has to endure the whole
year and for this reason it is generally stored in deep reservoirs to mitigate the effect of the
thick ice layer that forms during the winter season.
A common problem faced in this region is also the disposal of waste waters and solid
wastes. These may pass on diseases and pollute the environment. Several methods are used
for their elimination (physical-chemical, biological, grinding, incineration, etc.) (Harris,
1986).
In some areas with continuous and discontinuous permafrost as in Yakutia (Siberia),
there is extensive grain agriculture. Here, the thawing caused largely by agricultural
practices produces thermokarst phenomena (Czudek and Demek, 1970b) and machinery
frequently sinks in thaw holes. Usually, the alas topography makes agricultural works