Geomorphology applied to glacial regions
137
transported was 150 million tons. It is very difficult to plan a permanent road network in
the Skeidarfirsandur as a consequence of the high frequency of these floods.
Under the Myrdalsj6kull Ice Sheet the Karla volcano has an eruptive activity well
known since 1625. The last eruption was in 1918 and the discharge reached
200,000 m 3 s-1. The southern coast advanced 200 m as a consequence of this eruption,
and a progradation of 2.2 to 2.5 km has been estimated since 1660 (Bjornsson, 1979).
3. Problems derived from glaciotectonics
Deformations caused by glacial activity can produce locally severe disturbances in some
geological structures, resulting in folds, fractures, and genesis of breccia in the stratigraphic sequences, or in a reduction of the mechanical resistance of rocks and sediment.
Therefore, it is very important to have a detailed knowledge of these deformations,
because they can have consequences to ore mineral surveys, mining works, civil engineering, and soil mapping.
In some mines of western Canada important glaciotectonic activity has been recognized
(Aber et al., 1989): about 12,000,000 m 3 of coal have been mobilized by overthrusting and
a large depression was generated, and later covered with sediments (Figure 6.12). Because
the coal has been relocated closer to the surface, it has oxidized, thus reducing its caloric
value, and in addition it has increased in water content, so for these reasons it is not
exploited.
In other cases the substrate can be affected by glaciotectonic deformation, with a
consequent decrease in shear strength. Under these circumstances, slides of weakened
materials can affect roads and bridges, as occurs with the Upper Cretaceous argilites in
the South Saskatchewan River valley of Canada (Krahn et al., 1979).
X
X'
Glacier Flow
J
Transported Coal
Bedrock .........
Coal Subcrop
._
Zone
,,,,2~
" " Till " "
Figure 6.12. Schematic cross section showing the depression formed by glaciotectonism and the hill
located downglacier that includes some of the coal transported from the depression (after Aber et al., 1989).
137
transported was 150 million tons. It is very difficult to plan a permanent road network in
the Skeidarfirsandur as a consequence of the high frequency of these floods.
Under the Myrdalsj6kull Ice Sheet the Karla volcano has an eruptive activity well
known since 1625. The last eruption was in 1918 and the discharge reached
200,000 m 3 s-1. The southern coast advanced 200 m as a consequence of this eruption,
and a progradation of 2.2 to 2.5 km has been estimated since 1660 (Bjornsson, 1979).
3. Problems derived from glaciotectonics
Deformations caused by glacial activity can produce locally severe disturbances in some
geological structures, resulting in folds, fractures, and genesis of breccia in the stratigraphic sequences, or in a reduction of the mechanical resistance of rocks and sediment.
Therefore, it is very important to have a detailed knowledge of these deformations,
because they can have consequences to ore mineral surveys, mining works, civil engineering, and soil mapping.
In some mines of western Canada important glaciotectonic activity has been recognized
(Aber et al., 1989): about 12,000,000 m 3 of coal have been mobilized by overthrusting and
a large depression was generated, and later covered with sediments (Figure 6.12). Because
the coal has been relocated closer to the surface, it has oxidized, thus reducing its caloric
value, and in addition it has increased in water content, so for these reasons it is not
exploited.
In other cases the substrate can be affected by glaciotectonic deformation, with a
consequent decrease in shear strength. Under these circumstances, slides of weakened
materials can affect roads and bridges, as occurs with the Upper Cretaceous argilites in
the South Saskatchewan River valley of Canada (Krahn et al., 1979).
X
X'
Glacier Flow
J
Transported Coal
Bedrock .........
Coal Subcrop
._
Zone
,,,,2~
" " Till " "
Figure 6.12. Schematic cross section showing the depression formed by glaciotectonism and the hill
located downglacier that includes some of the coal transported from the depression (after Aber et al., 1989).