Tropical landforms
577
During the symposium a karst climatic zonality was recognized, including the
differentiation of karst landforms of humid tropical zones, among others. These forms
mainly develop on tropical zones with carbonate outcrops associated with alpine ranges;
the Greater Antilles, some regions surrounding the Caribbean Sea, southeast Asia,
Indonesia, New Guinea and several African zones.
Some significant differences exist between tropical karst and other karst types
developed in other climates. Firstly, carbonate dissolution is more rapid due to the higher
content of biogenic CO2 (Birot, 1954, 1966; Ford and Williams, 1989). Secondly, strong
precipitation produces intense slope gullying, giving rise to irregular closed depressions.
Finally, high evaporation rates induce calcium carbonate precipitation forming very hard
caprocks on the steep slopes, which often is considered as the main cause of their great
inclination (Sweeting, 1972).
Tropical karst landforms are usually divided into two types: kegelkarst (cone karst) and
turmkarst (tower karst). Differentiation is made as a function of hill morphology. In the
future it is possible that the classification be based, more logically, on the morphology of
closed depressions (Sweeting, 1972). Balazs (1973) proposed a tropical karst differentiation mainly based on morphometric considerations and distinguished three types: doline
karst, cone karst and tower karst. Cone karst hills are 30 to 120 m high and have a density
of 15 to 30 hills/km 2, whereas in tower karst heights fluctuate between 100 and 300 m and
their density is about 5 to 10 hills/km 2.
Many factors influence the development of these forms. Limestone types seem to play
an important role. Jamaican cone karst hills are located on very fissured limestones
(Sweeting, 1958; 1972), whereas karst towers in Puerto Rico (Monroe, 1964) and those of
Sarawak (Malaysia) (Wilford and Wall, 1965) develop on crystalline limestones with soft
interbedded levels. Bedding strike and dip affect form development in such a way that hills
and depressions opened at their toes (dolines, uvalas, poljes, and valleys) elongate
following those directions. In the same sense, splitting planes affect landform
development.
No clear relationship exists between total precipitation and type of tropical karst. In his
studies on New Guinea, Verstappen (1964) indicated that a precipitation of at least
1500 mm is needed for the cone karst to develop. In China, the cone karst region of
Schuicheng has an average annual precipitation of 1230 mm and the tower karst zone of
Guilin, the most spectacular one in China, has an annual rainfall of 1870 mm (Sweeting,
1995). In order to make comparisons, seasonality, intensity of precipitation, and
temperature also need to be known, because altitudinal variations clearly influence cone
karst development.
Water infiltration is favored by the open-joint network, which controls surface
drainage. Despite allogenic rivers, which usually have large discharges, the drainage
pattern is constituted by dry valleys, blind valleys ending in a ponor, and steephead valleys
that begin in a spring (cul-de-sac). Superficial associated forms are bare and covered
karren, dolines of different types, uvalas, and poljes. The rapid and intense infiltration of
water into the karst massif gives rise to an important cave system, mainly horizontal,
embracing a long and complex history of tropical karst development (Barbary et al., 1991;
Sweeting, 1995). Caves generate more easily in the zone of fluctuating phreatic level,
characterised by a greater dissolution (Jennings, 1985).
577
During the symposium a karst climatic zonality was recognized, including the
differentiation of karst landforms of humid tropical zones, among others. These forms
mainly develop on tropical zones with carbonate outcrops associated with alpine ranges;
the Greater Antilles, some regions surrounding the Caribbean Sea, southeast Asia,
Indonesia, New Guinea and several African zones.
Some significant differences exist between tropical karst and other karst types
developed in other climates. Firstly, carbonate dissolution is more rapid due to the higher
content of biogenic CO2 (Birot, 1954, 1966; Ford and Williams, 1989). Secondly, strong
precipitation produces intense slope gullying, giving rise to irregular closed depressions.
Finally, high evaporation rates induce calcium carbonate precipitation forming very hard
caprocks on the steep slopes, which often is considered as the main cause of their great
inclination (Sweeting, 1972).
Tropical karst landforms are usually divided into two types: kegelkarst (cone karst) and
turmkarst (tower karst). Differentiation is made as a function of hill morphology. In the
future it is possible that the classification be based, more logically, on the morphology of
closed depressions (Sweeting, 1972). Balazs (1973) proposed a tropical karst differentiation mainly based on morphometric considerations and distinguished three types: doline
karst, cone karst and tower karst. Cone karst hills are 30 to 120 m high and have a density
of 15 to 30 hills/km 2, whereas in tower karst heights fluctuate between 100 and 300 m and
their density is about 5 to 10 hills/km 2.
Many factors influence the development of these forms. Limestone types seem to play
an important role. Jamaican cone karst hills are located on very fissured limestones
(Sweeting, 1958; 1972), whereas karst towers in Puerto Rico (Monroe, 1964) and those of
Sarawak (Malaysia) (Wilford and Wall, 1965) develop on crystalline limestones with soft
interbedded levels. Bedding strike and dip affect form development in such a way that hills
and depressions opened at their toes (dolines, uvalas, poljes, and valleys) elongate
following those directions. In the same sense, splitting planes affect landform
development.
No clear relationship exists between total precipitation and type of tropical karst. In his
studies on New Guinea, Verstappen (1964) indicated that a precipitation of at least
1500 mm is needed for the cone karst to develop. In China, the cone karst region of
Schuicheng has an average annual precipitation of 1230 mm and the tower karst zone of
Guilin, the most spectacular one in China, has an annual rainfall of 1870 mm (Sweeting,
1995). In order to make comparisons, seasonality, intensity of precipitation, and
temperature also need to be known, because altitudinal variations clearly influence cone
karst development.
Water infiltration is favored by the open-joint network, which controls surface
drainage. Despite allogenic rivers, which usually have large discharges, the drainage
pattern is constituted by dry valleys, blind valleys ending in a ponor, and steephead valleys
that begin in a spring (cul-de-sac). Superficial associated forms are bare and covered
karren, dolines of different types, uvalas, and poljes. The rapid and intense infiltration of
water into the karst massif gives rise to an important cave system, mainly horizontal,
embracing a long and complex history of tropical karst development (Barbary et al., 1991;
Sweeting, 1995). Caves generate more easily in the zone of fluctuating phreatic level,
characterised by a greater dissolution (Jennings, 1985).