Geology Reference
In-Depth Information
()
a
Altitude
(m)
Normal streamsink
Partly vegetated channel
taking flood water
Perennial watercourse
1,250
Half-blind valley
1,224 m
1,228 m
1,225
Stream in swamp
0
100 m
1,200
()
b
1,075
Plateau surface
Blind valley
Doline
Doline
Stream in
swamp
1,050
The Bath
House
Cave
1,025
1,000
0
100 m
975
Figure 8.11
Blind and half-blind valleys in New South Wales, Australia. (a) A half-blind valley on Cooleman Plain.
(b) A blind valley at Yarrangobilly.
Source:
Adapted from Jennings (1971, 110, 111)
a craggy dry valley in which the stream fed by Malham
Tarn formerly flowed over the limestone to cascade over
the 75-m cliff of Malham Cove (Figure 8.12; Colour
Plate 4).
Extensive dry valley networks occur in some areas
of karst. An impressive set is found in the White
Peak, England. Here, a few major streams - the Rivers
Manifold, Dove, and Wye - flow across the region, but
most other valleys are dry (Figure 8.13). Many of the
dry valleys start as shallow, bowl-like basins that develop
into rock-walled valleys and gorges. Other, smaller dry
valleys hang above the major dry valleys and the perma-
nent river valleys. The origin of such networks is puzzling
but appears to be the legacy of a former cover of impervi-
ous shales (Warwick 1964). Once the impervious cover
was removed by erosion, the rivers cut into the limestone
beneath until solution exploited planes of weakness and
diverted the drainage underground. The 'hanging val-
leys', which are reported in many karst areas, resulted
from the main valleys' continuing to incise after their
tributaries ceased to have surface flow.
Meander caves
Meander caves
are formed where the outer bend of a
meander undercuts a valley-side. Now, stream debris does
not hamper rivers from lateral erosion in karst landscapes
as it does rivers on other rocks, because rivers carrying
a large clastic load cannot move laterally by corrasion
as easily as rivers bearing a small clastic load can by
corrosion. For this reason, meander caves are better devel-
oped in karst terrain than elsewhere. A prime example is
Verandah Cave, Borenore, New South Wales, Australia
(Figure 8.14).
