Geology Reference
In-Depth Information
Plate 8.18
Helictites in Ogof Draenen, Pwll Ddu, South Wales.
(
Photograph by Clive Westlake
)
HUMAN IMPACTS ON KARST
swiftly finds its way underground, where it blocks pas-
sages, diverts or impounds cave streams, and chokes cave
life.
The prevention of soil erosion and the maintenance
of critical soil properties depend crucially upon the
presence of a stable vegetation cover. The Universal Soil
Loss Equation or its more recent derivatives (p. 179)
can predict soil erosion on karst terrain, but higher
rates may be expected on karst as compared with most
other soil types because features of the geomorphology
conspire to promote even greater erosion than else-
where. In most non-karst areas, soil erosion depends
upon slope gradient and slope length, as well as the
other factors in the USLE. It also depends partly on
slope gradient and slope length in karst terrain but,
in addition, the close connections between the surface
drainage system and the underground conduit system
produce a locally steeper hydraulic gradient that pro-
motes erosive processes. Moreover, eroded material in
karst areas has a greater potential to be lost down joints
and fissures by sinkhole collapse, gullying, or soil strip-
ping. An adequate vegetation cover and soil structure
(which reduce erodibility) take on a greater significance
in lessening this effect in karst areas than in most other
places.
Surface and subsurface karst are vulnerable to human
activities. Caves are damaged by visitors, and agricultural
practices may lead to the erosion of soil cover from karst
areas.
Soil erosion on karst
Karst areas worldwide tend to be susceptible to
soil
erosion
. Their soils are usually shallow and stony, and,
being freely drained, leached of nutrients. When vegeta-
tion is removed from limestone soils or when they are
heavily used, soil stripping down to bedrock is com-
mon. It can be seen on the Burren, Ireland, in the
classic karst of the Dinaric Alps, in karst of China,
in the cone karst of the Philippines, and elsewhere.
In Greece, soil stripping over limestone began some
2,000 years ago. The limestone pavement above Malham
Cove (Colour Plate 4) may be a legacy of agricultural
practices since Neolithic times, soils being thin largely
because of overgrazing by sheep. Apart from resulting
in the loss of an agricultural resource, soil stripping has
repercussions in subterranean karst. The eroded material
