84
Climatic Geomorphology
Figure 3.22. Hanging valley. Western coast of Norway. Photo: J. L6pez-Martfnez.
thermal mantle and allows the disappearance of the permafrost so that clasts can easily be
evacuated by the glacier. The generation of a concave sheeting subparallel to the crosssectional section helps the attainment of the parabolic profile and of its perpetuation. The
disposition of the extensive and compressive glacial flow of Nye (1952) partially explains
the existence of thresholds and basins (Fig. 2.23). In compressive zones an increase of
erosion takes place and once irregularities have appeared they tend to be conserved or even
accentuated.
Sometimes, the thickness or height level of glaciers increases because of blocking
by another glacier, or due to superior feeding rather than evacuation. In these cases, a glacier
can find a preglacial breach in the rim of the watershed to unload into an adjacent valley.
Such breaching can also produce glacial erosion and is able to produce a U-form and even
to form rocky basins (Penck, 1905). These passes are denoted as glacial diffiuence. In the
A
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p,."
l l ~ J t r4:" ~ t
j
~
~
-- .,." ",.. _,,J4l.l
~F/r/~' ~. . dt ~
I .
,-=-__- -=_ .......
...,-~,,~/<~
-..
,
I
~
-~
,.-,-.,.: t-.~ -~Za
! ".q ' :~~~e~'.~,-~i
~ ~
9
F ....
"_,~:,_aP.-:
,,,..
.......L . ;~--~--," t .:/~,,'/-~-'~.~.~,'~,Y;
"' /'I,
r-.,-~~_~:.~_-~:
~...~:,~~.,_._,,.~
'
: o,
9 a~ "
~~~;.,?-,:
--.~-, ,,,,m. ,-..:,,,~..,2,...v-,:, ,,
Figure 3.23. Longitudinal profile illustrating the development of a glacier staircase, because of the
different joint spacing. AA- represents the preglacial profile and BB- the glacier staircase. The areas d, dl
and d2 are zones of difficult excavation by the glacier, due to the joint spacing; the opposite occurs in c and
Cl. Arrows indicate the direction of the ice movement (Matthes, 1930).