ENDINS, n.' 13. 1987. Ciutat de Mallorca. |
KARST IN SOUTHERN AFRICA
by Margaret E. MARKER * and Frances M. GAMBLE **
En el presente trabajo se revisa la distribución de las rocas karstificables en ,África meridional,
distinguiendo entre dos clases predominantes: las calizas dolomiticas proterozoicas de textura espa-
ritica, propias de las mesetas interiores, y las calizas arenosas terciarias de la costa, cuya textura es
micritica. La densidad de formas kársticas superficiales es variable y comparativamente baja en re-
lación con otras regiones. Las cuevas corresponden a un origen freático-somero y pueden contener
abundantes espeleotemas. Se han podido detectar dos fases principales de crecimiento, aunque la
precipitación moderna es menos intensa. El más importante periodo de karstificación puede ser atri-
buido a tiempos considerablemente remotos.
Los impactos ambientales sobre el karst de África meridional abarcan desde cambios en la hi-
drogeología debido a la extracción de agua con fines económicos, pasando por el drenaje de minas
y las modificaciones en la cubierta superficial, hasta efectos directos resultantes de actividades mi-
neras, en especial para la obtención de oro, de guano de murciélago y primitivamente de espeleote-
mas. Algunas rocas madres son empleadas en mineria para su aprovechamiento en la fabricación
de acero. Hasta ahora los problemas causados por la contaminación son de escasa importancia. Las
cuevas situadas cerca de los principales centros de población sufren impactos de utilización que a
menudo pasan inadvertidos. Las consecuencias de nuevas instalaciones militares, junto a Bredas-
dorp están siendo objeto de seguimiento. En África meridional se cuenta con las bases necesarias
para la realización de programas efectivos de gestión ambiental.
The paper reviews the distribution of karst rocks in southern Africa and distinguishes between
t w o dominant types: the sparitic Proterozoic dolomitic limestones of the interior plateaux and the
Tertiary micritic sandy limestones o f the coast. The density of surface karst forms is variable and
l o w b y comparison with overseas regions. Caves are shallow phreatic in origin and may contain
massive speleothem development. Two major phases of growth are recognised. Modern precipita-
tion is minor. The major karst forming period is believed to be of considerable antiquity.
The impacts o n southern African karst range from changes to the geohydrology due to econo-
mic extraction, mine dewatering and changes t o the surface cover, to direct effects of mining parti-
cularly for gold, for bat guano and formerly for speleothems. Some host rock is directly mined for
use i n steel making. Pollution is so far of minor importante. Caves near major population centres
suffer user impact which is often inadvertent. The consequences of a new militan/ installation near
Bredasdorp are being monitored. In southern Africa the basis exists for effective management pro-
Potential karst host rocks cover 50.000 km2 in
cient rocks. Chemically they are not true dolomites,
Southern Africa'. This is 1.9 % of the total area.
being CaMg(C03)z rather than CaC03.MgC03, and
There are two extensive karst host rock types (Ta-
they do not weather to dolomitic gruss. Beds with
ble l ) : the Proterozoic dolomitic limestones of the
low magnesiurn ratios, almost pure limestones, oc-
interior plateaux and, secondly, the Tertiary Coas-
cur in the middle sequence (Button, 1971). Although
tal Lirnestones2. The dolomitic limestones are re-
deposited in separate, shallow tidal basins, the
sistant, sparitic, well-jointed and highly lithified an-
Transvaal Sequence containing the Chuniespoort
Fort Hare University
Defined as the Republic of South Africa as of 1960, Namibia,
P. Bag X 1314
Botswana, Lesotho and Swaziland.
Alice 5700. Rep. of the Ciskei
* The informal terrn Coastal Lirnestone was coined by Siesser
(1972) t o include the Langebaan Formation, the Alexandria For-
Raedene. Johannesburg 2124. Rep. of South Africa
rnation, the Bredasdorp Fomation and the Uloa Formation.
Formation and the less extensive Duitschland Forma-
Surface karst forms have a low density overall
tion of the Malmani Subgroup are similar lithologi-
and strongly karstified areas are very localised. In-
cally to the Campbell Rand Group of the Griqualand
land above the Great Escarpment the karst land-
West Sequence of the Northern Cape Province (Brink,
forms are of considerable antiquity, apparently
1979). Both Sequences exhibit considerable stroma-
being initiated contemporaneously with the evolu-
tolite and algal dome development resulting from
tion of the mid-Cenozoic African planation surface.
deposition in a tidal lagoonal environment (Eriks-
The almost ubiquitous presence of insoluble terra
rossa type residues limits surface karst expression
In contrast, the coastal limestones are soft, va-
and causes infilling of hollows and blocking of ma-
riably pure, weakly jointed and dominantly micritic,
jor cave systems.
sandy limestones. These Coastal Limestones out-
Virtually al1 major caves are shallow phreatic
crop discontinuously on land around the coast of
in origin, drought restricting the presence of point
southern Africa from Saldanha Bay to Zululand,
input and therefore vadose development. Speleo-
but on the Continental Shelf are more continuous
thems are massive in some caves, indicating two
(Siesser, 1972; Fig. 1). In addition there are also
major periods of deposition interrupted by resolu-
areas of Palaeozoic Damara marble and associated
tion. Recent deposition is on a small scale only.
limestones in Namibia and western Botswana. Pa-
Below the Great Escarpment the karst of the
laeozoic Cango Limestones outcrop within the Cape
Coastal Limestones is associated with a suite of
Fold Belt and Tertiary calcretic, impure limestones
Cenozoic marine benches from 250 m altitude to
have limited occurrence along the inner margin of
below present sea level (Marker, 1985). The highest
the Namib desert. There is a basic division bet-
density and largest amplitude surface karst forms
ween ancient, hard carbonate rocks above the Great
are associated with the 240 m and 200 m benches
Escarpment and the younger, softer micritic lime-
(Marker and Sweeting, 1983; Russell, 1985), also
stones below. The only exceptions are the Damara
suggesting a mid-Tertiary period of maximum de-
marble outcrops within the Namib desert and the
velopment. Caves are rare with the exception of
Cango Limestone outcrop.
the Bredasdorp area, where they tend to be prefe-
B O T C W A N A
DANIARA SYSTEM m
CANGO LIMESTONE m
COASTAL LIMESTONE O
Figure 1: Karst areas of southern Africa
(A = Apocalypse, C = Cango, D = Drotsky's Caves,
E = Echo, L = Lobatse Caves, M = Makapansgat,
S = Sterkfontein, Su = Sudwala, W = Wolkbergi.
RAINFALL (mm) AREA (km2)
Central and N Transvaal
450 - 600
200 - 400
Griqualand West Sequence
(rnarble and limestone)
200 - 400
500 - 700
500 - 700
Table 1: Karst areas of Southern Africa
rentially located beneath the 60 m and 30 m benches.
semi-arid characteristics of the areas in which most
The cohesive strength of the Coastal Limestones in
of them have formed through phreatic processes.
most areas restricts cave development. Neverthe-
Resultant cave dirnensions are small, cave entran-
less the existence of major springs with distinct
ces are usually single, cave temperatures are com-
chernical characteristics suggests that the ' exis-
paratively high and cave systems are generally
tence of major conduits is far more general than
the existence of enterable caves.
A nurnber of caves intersect the water table
The best-known karst areas are the central and
with a resultant occurrence of underground pools
south-western Witwatersrand, in the vicinity of
or lakes such as that in Sterkfontein. Running wa-
Sterkfontein and Carletonville respectively (Brink,
ter is known in only 1 % of the dolomite and lirnes-
1979; Gamble, 1981; Moon, 1973), the north-east-
tone caves. This means that weathering and ero-
ern Transvaal (Marker, 1985), and the Alexandria
sion processes are usually very slow and that the
and Bredasdorp areas on the Coastal Lirnestones
food chain is very limited in the majority of caves
(Marker, 1981; Marker and Sweeting, 1983; Rus-
(Garnble, in press).
sell, 1985). Elsewhere isolated cites have been in-
The major threats to the cave ecosystem are
vestigated as in the Namib (Sweeting and Lancas-
associated with urban and peri-urban sprawl and
ter, 1984; Marker, 1982), but much more detailed
with major development projects such as the cons-
work is required.
truction of roads. They are manifiest in both sur-
face and subsurface disturbances, and most com-
rnonly include extraction, construction, pollution
lmpacts on Southern
especially of air and water, research and recreation
irnpacts (Fig. 2).
Af rican Caves
EXTRACTION affects both the host rock and its se-
Southern African caves are particularly distinc-
condary contents such as water.
tive and vulnerable because of the resistant nature
- Dolomite and limestone are used as flux or as a
of the host rocks, especially the dolomites, and the
source of manganese for the metallurgical in-
dustries, posing ever-increasing threats to the
present a borehole project of the Department of
karst areas, including the caves.
Water Affairs threatens extensive karst areas in
- At approximately the turn of the century speleo-
the central Witwatersrand as a result of major
thems were extracted during small-scale min-
water extraction schemes to alleviate the cu-
ing operations in order to produce slaked lime
for the building industry. At present extraction
The impact of increasing peri-urban sprawl,
of speleotherns is confined mainly to limited re-
particularly in the areas close to Johannesburg,
rnoval for research purposes, o r t o more exten-
is already evident in the number of long-term
sive rernoval as part of the casual vandal and
boreholes which have dried out as a result of
the increasing demand for water on the small-
Since the late nineteenth century deposits of
holdings in the area.
bat guano in local caves have been excavated
by farmers as a source of fertilizer.
CONSTRUCTION and the provision of services are
- In semi-arid to arid areas, where surface water
associated with al1 development activities jn karst
supplies are lirnited, increasing reliance is plac-
areas. The specific disturbances associated with
ed on ground water. Lowering of the water ta-
these alterations are several and complex, manifest
ble results frorn pumping to facilitate sub-water
mainly in the alteration, of surface water-flow pat-
table mining, and the provision of water for sur-
terns and the consequent dehydration of karst and
face activities such as irrigation, and industrial
cave areas. In al1 instances there is encroachment
and domestic developments. Sub-water table
of artificial surfaces in the form of roads, buildings,
mining is extensive near Carletonville. In 1970
parking lots, agricultura1 lands and some levelling
the town of Bank had to be abandoned because
of the area by infilling. All such activities decrease
of the hazards resulting from sinkhole develop-
percolation and increase surface runoff.
ment consequent upon the dewatering of the
lncreased loading by surface structures may also
dolomite for gold mining on the West Rand. At
have some impact, particularly where instability of
Dept. of Water Affairs, Forestry
Permits to enter forest and
and Environmental Conservation
Act protecting geological forrns
Act proctecting individual sites
e.g. Sterkfontein Cave
Mines and Minerals
Act pertaining t o darnage throug~h
Dept. of Defence
Permits t o enter militan/ areas
Perrnits to enter hornelands
Deterrent notices at caves
Provincial Nature Consewation
Legislation and !3añger control
PRIVATE PROPERTY OWNERS
Subjective control - mainly acces,
e.g. Sudwala Cave and
Restricted access t o sites,
e.g. Makapan Cave
Gem and Mineral Clubs
Table 2: Parties to whorn cave rnanagernent is of concern in southern Africa
(after: Garnble, 1981b).
TYPE OF DISTURBANCE
Enlarging access points
Mining and Quarrying
Floral and faunal
Roads and access
Urban and Industrial
Noise and vibrations
Partial /Total subrnergence
Agriculture and Forestry
Air - herbicides
Water - sewage
Offal, including litter
Figure 2: Summary of the disturbances and their impacts on a
karst cave ecosystem.
These disturbances are regarded as posible, their oc-
currence and magnitude being dependent upon the
cave itself and the nature of the disturbance.
Haste and thoughtlessness
Carrying Capacity of cave
o f general population
Srnall, inaccesible caves
Paucity o f caves i n
lncreased leisure and
Table 3: Problems of karst cave managen
nent in southern Africa (after: Gamble, 1981b).
underlying rock occurs. Vibrations, rnainly as a re-
access and legislative.control such as the National
sult of blasting, noise and heavy vehicle rnovernent
Monuments Act, the Forestry Act and the Trans-
may result in increased joint dirnension and in da-
vaal Nature Conservation Ordinance.
rnage particularly to cave systerns.
The problerns associated with cave conserva-
The current developrnent on the De Hoop Nature
tion are similar throughout the world, although
Reserve at Bredasdorp has been a source of natio-
each area has certain unique aspects (Table 3). In
nal concern because of the anticipated possible irn-
southern Africa the basis exists for future rnanage-
pacts on the karst and cave area.
rnent prograrnrnes and several advantages exist in
cornparison with other parts of the world particu-
POLLUTION is derived in varying ways and to vary-
larly in terms of time and circurnstance.
ing degrees frorn al1 activities in a karst area. It is
usually inadvertent, in association with atrnosphe-
ric, hydrological and solid waste pollution, result-
ing in the accurnulation of gases, aerosols and che-
micals. Atrnospheric pollution is probably the least
obvious, while water pollution is the rnost ubiqui-
BUTTON, A. (1971): The stratigraphic history of the Malmani Do-
tous. In many areas rernote frorn urban and indus-
lomite in the eastern and northeastern Transvaal. Trans.
Geol. Soc. S A, 74,229-247.
trial areas karst regions are subject to solid waste
BRINK, A.B.A. (1979): Engineering geology of southem Africa. V. 1.
disposal in caves and sinkholes, the consequences
of which rnay be long-terrn and drarnatic.
ERIKSSON, K.A. (1977): Tidal flat and subtidal sedimentation in
the 2250 MY Malmani Dolomite, Transvaal, South Africa. Sed.
Geol., 18, 223-244.
RESEARCH AND RECREATION of necessity irnpact
GAMBLE, F.M. (1980): Disturbance of underground wilderness in
karst areas and especially the caves as there is in-
karst caves. lnt Jour. Envir. Stud., 18( 1 ), 33-40.
creasing pressure on wilderness areas. Darnage to
GAMBLE, F.M. (1981a): The resource potential of Transvaal caves.
caves is rnost often in the forrn of cornpaction and
8th. lnt Cong. Speleol. Proceeúings. 466-468.
abrasion, and is usually inadvertent. However, the
GAMBLE, F.M. (1981b): Problems of management of Transvaal
caves. 8th lnt Cong. Speleol. Proceeúings. 46947 1.
irnpacts are usually more direct on a cave systern
GAMBLE, F.M. (in precs): Caves.
and are very often irreversible. Tourists, scientists,
MARKER. M.E. (1981): Karst in the Bredasdorp area: a prelimina
cavers and casual visitors to caves al1 affect the
analysis. S A Geogr., 9,29-30.
cave ecosystern to varying degrees.
MARKER. M.E. (1982): Aspects of Namib geomorphology: a doli
karst. Palaeoecol. Africa., 15, 187-199.
Awareness of caves which require conservation
MARKER, M.E. (1985):Karst areas of southern Africa 1st. Int. Co
in their own right and for the protection of visitors
Geomorph. In Ress.
is recent. Over time efforts at cave conservation in
MARKER. M.E. and SWEETING. M.M. (1983): Karst devel
South Africa have taken several forrns (Table 2),
on the Alexandria Coastal Limestone, eastern Cape P
such as legislative controls, the construction of ga-
South Africa. Zeit. f. Geomoph., 27, 21-38.
MOON, B.P. (1973): Factors mntrolling the development of cav
tes at cave entrances, the restriction of access by
in the Sterkfontein area. S A Geog. Jour., 54, 145-151.
landowners, and educational prograrnrnes under-
RUSSELL, L. (1985): Karst development: the application of a sy
taken by concerned scientists and speleologists.
tems model. 1st Int. Geomoph. Conf. In press.
The rnost irnportant of the controls operating to
SIESSER, W.G. (1972): Petrology of the Cainozok Coastal Lime-
stones of Cape Province, Trans. Gml. Soc. SA., 75, 178-185
protect the 'Southern African caves are cultural he-
SWEETING, M.M. and LANCASTE
sitation; the natural protection afforded by cave lo-
cation and configuration; landowner control over