Geology Reference
In-Depth Information
Figure 8.4
The karst drainage system: storages and flows.
Source:
Adapted from Ford and Williams (1989, 169)
Each zone has particular hydraulic, chemical, and hydro-
logical properties, but the zones expand and contract with
time and cannot be rigidly circumscribed.
The chief geomorphic processes characteristic of karst
landscapes are solution and precipitation, subsidence,
and collapse. Fluvial processes may be significant in
the formation of some surface and subterranean land-
forms. Hydrothermal processes are locally important in
caves. A distinction is often drawn between
tropical
karst
and karst in other areas. The process of karstifi-
cation is intense under tropical climates and produces
such features as towers and cones (p. 201), which
are not produced, at least not to the same degree,
under temperate and cold climates. Discoveries in north-
west Canada have shown that towers may form under
cold climates (pp. 201-2), but the widespread dis-
tribution of tropical karst testifies to the extremity
of limestone solution under humid tropical climatic
regimes.
SOLUTION AND PRECIPITATION
Limestone, dolomite, and evaporites
As limestone is the most widespread karst rock, its solu-
tion and deposition are important karst processes. With
a saturation concentration of about 13 mg/l at 16
◦
C
and about 15 mg/l at 25
◦
C, calcite has a modest solu-
bility in pure water. However, it is far more soluble in
waters charged with carbonic acid. It also appears to be
more soluble in waters holding organic acids released
by rotting vegetation, and is very soluble in waters con-
taining sulphuric acid produced by the weathering of
sulphide minerals such as pyrite and marcasite. Carbonic
acid is the main solvent in karst landscapes, limestones
readily succumbing to carbonation (p. 56). Dolomite
rock behaves similarly to limestones in natural waters,
although it appears to be slightly less soluble than lime-
stone under normal conditions. Complexities are added
