52
Climatic Geomorphology
i l l
[
(b) ~'~'~"
~
~ REGELATION ICE
~"1~1~
,
Figure 2.21. Influence of bed irregularities on the ice flow. (a) Process of basal plastic flow, sight in plan
view (Weertman, 1957). (b) Sliding mechanism by refreezing, in section (Kamb and LaChapelle, 1964).
speeds of a glacier are obtained by installing stakes in the ice and locating a theodolite on
fixed points of the rocky margin. In order to obtain the speed at depth, borings to the base
are carried out (Fig. 2.20) and later a flexible tube is introduced into the conduit. By means
of a clinometer the movement can be followed. The speed is higher in the upper part than
in the lower.
Some valley glaciers experience fast and abnormal flows in which the ice mass
moves as a wave at speeds of up to one hundred times the average value and with
displacements up to 11 km. They are known as glaciers with spasmodic flows or surging
glaciers (Fig. 2.22). Vibrations and intense noises accompany their sudden movements
(Meir and Post, 1969; Sharp, 1988; Clarke, 1991; Dowdeswell et al., 1991; Evans,
2004a). These swellings can have a regularity of a few years to several centuries. In the
glacier they cause the presence of deformed chaotic surfaces, intensely sheared margins,
great changes in its thickness and strongly folded medial moraines. The intense shear at
the margins of surging glaciers can produce foliation in the ice (Pfeffer, 1992). In
Svalbard 504 surge-type glaciers have been described. These glaciers result from a
polythermal regime and fine-grained deformable beds (Jiskoot et al., 2000). High
pressures of the subglacial water motivate these fast flows and can produce catastrophic
advances. The surge outbreak can also be associated with seismic activity and important
modifications in precipitation.
Stress regimes (Fig. 2.23) vary throughout the length of the glacier and compressive
flow occurs as the speed of the glacier reduces (Nye, 1952), in such places as below
steep sections of the glacier. The sliding planes are curved in an ascending direction and
Climatic Geomorphology
i l l
[
(b) ~'~'~"
~
~ REGELATION ICE
~"1~1~
,
Figure 2.21. Influence of bed irregularities on the ice flow. (a) Process of basal plastic flow, sight in plan
view (Weertman, 1957). (b) Sliding mechanism by refreezing, in section (Kamb and LaChapelle, 1964).
speeds of a glacier are obtained by installing stakes in the ice and locating a theodolite on
fixed points of the rocky margin. In order to obtain the speed at depth, borings to the base
are carried out (Fig. 2.20) and later a flexible tube is introduced into the conduit. By means
of a clinometer the movement can be followed. The speed is higher in the upper part than
in the lower.
Some valley glaciers experience fast and abnormal flows in which the ice mass
moves as a wave at speeds of up to one hundred times the average value and with
displacements up to 11 km. They are known as glaciers with spasmodic flows or surging
glaciers (Fig. 2.22). Vibrations and intense noises accompany their sudden movements
(Meir and Post, 1969; Sharp, 1988; Clarke, 1991; Dowdeswell et al., 1991; Evans,
2004a). These swellings can have a regularity of a few years to several centuries. In the
glacier they cause the presence of deformed chaotic surfaces, intensely sheared margins,
great changes in its thickness and strongly folded medial moraines. The intense shear at
the margins of surging glaciers can produce foliation in the ice (Pfeffer, 1992). In
Svalbard 504 surge-type glaciers have been described. These glaciers result from a
polythermal regime and fine-grained deformable beds (Jiskoot et al., 2000). High
pressures of the subglacial water motivate these fast flows and can produce catastrophic
advances. The surge outbreak can also be associated with seismic activity and important
modifications in precipitation.
Stress regimes (Fig. 2.23) vary throughout the length of the glacier and compressive
flow occurs as the speed of the glacier reduces (Nye, 1952), in such places as below
steep sections of the glacier. The sliding planes are curved in an ascending direction and