Karst and caves of Madagascar

by Cavers Digest

Jan Myburgh, from Cavers Digest 5434, topic 7

I would like to visit Madagascar in future - with the purpose of studying their caves and cave life. Does anybody know the name and address of somebody who can help me. Has any biospeleological work been done in Madagascar?

Jan Myburgh

Nick Williams, from Cavers Digest 5436, topic 10

Just in case no-one better informed replies to this, yes there have been explorations and biospeleolgy done in Madagascar. The report reference is:

Crocodile Caves of Ankarana. WALTERS, Roo (ed). 1986.

The copy of the report I have says "further copies of this report may be obtained from Phil Chapman, Bristol Cuity Museum, Bristol, BS8 1RL." Failing that try somewhere like Bat Products or Inglesport:

Other participants in the trip included Jane Wilson, Dave Checkley, Simons Fowler, Mick McHale, Sheila Hurd and Paul Stuart. I can get hold of addresses for (some of) them IF you get stuck.

Bruce W. Rogers, from Cavers Digest 5437, topic 5

Madagascar, the fourth largest island on Earth, is part of a large plateau that is inclined westwards towards the Mozambique Strait. It has formed by the uplift of a large block of crust along a pair of faults that lie along both its eastern edge (East Coast fault) and another in the Mozambique Channel. These were formed at least 205 MYBP (million years before present) in the Early Jurassic, but perhaps as far back as the Permian Period of about 250 MYBP. The plateau includes the Comoro Islands about 500 km to the NW, the Seychelles Islands 1000 km to the N, and the Cargados Islands 1,000 km to the E. Originally part of Gondwanaland, Madagascar, Africa and S. America split from India and Antarctica some 180 MYBP. Subsequently, Madagascar drifted east from Africa at about 165 MYBP where it has stayed ever since. A series of elevated erosional terraces dating back to the Jurassic make the island look like a poorly formed layer cake. Mammals made the crossing of the Mozambique Channel nearly 40 million years ago, followed not too closely by wo/man roughly 1,700 years ago.

The island's metamorphic and igneous core of intensely deformed granites and gneiss rises along a NNE-aligned linear dome of nearly 2700 m high. Included in this core are small stringers of marble nearly 1.9 billion years old. No caves are currently known in these rocks as they are thin and interlayered with other quartz-rich rocks.

The next younger rocks of interest are the Mesozoic sedimentary rocks that lie on a belt nearly 150 km wide along the western coast. These rocks include Cretaceous limestones that make a thick arc just north of the western coastal "bulge", running from the city of Mahajanga north to the area of Nosy Be. A thin, 25 km wide "tail" of limestone starts just inland from Cape St. Andre on the north side of the west coast "bulge" and parallels the western side of the island some 100 km inland; it finally peters out near Onilahy near the SW tip of the island in spiny desert. Fossil reef corals, lampshells (brachiopods) , snails, and even a few crocodile fossils are known. Interlayers of sandstones, shale, and even some volcanic rocks reveal relatively gently westward-dipping bedding in the near vertical walls of carbonate rocks.

These rocks are the most important as they have the major karst areas. The karst is probably old - a relic of the wetter times in the Miocene some 20-12 million years ago - as currently the climate is rather dry with a savannah and scrub forest present (the current practice is to burn the highland grasslands [once a mixed savannah and forest tapestry] in hopes of green pasture . . . meanwhile the rivers bleed red with clay-rich top soil). Especially in the extreme NW tip of the northern Ankarana massif, areas of 30 m high pinnacle karst or spitzkarren are found as well as areas of collapsed doline karst. The pinnacle karst is so difficult to traverse that helicopters are used by scientific parties to gain access. The sinkhole karst is pocketed with many collapse sinks that hold miniature sunken forests. Caves in this area are said to have white blind fish . . . and, reportedly, a few crocodiles waiting for unwary biologists and cavers. Small colonies of both insect- and fruit-eating bats also live in the karst. Fossil skeletons of lemurs have also been washed into these caves. In a limestone grotto at the extreme N tip of the island near Antsiranana - a site named Anja after an archaeologist's daughter - the oldest early wo/man site is found with its pottery sherds, animal bones, and cooking ashes date to about 750 AD. Artifacts from Arab traders in the eleventh century overlies these deposits, which are sequestered under later Malagasy and French relics.

Other limestone areas in the Cretaceous limestones, as well as other Tertiary and quaternary deposits, with reports of caves include the Permian limestones filled with lamp shells and snail fossils near Vohitloa near city of Toliara. Some basalt is present on the island, but it is unclear if lava tubes are present.

Madagascar is a poor nation that has doubled in population over the last 25 years to 11 million persons speaking both Malagasy and French. Cattle, rice, cloves, vanilla, and coffee as well as minerals including graphite for pencils, gems like beryl, plus a little lead, copper, tantalium, niobium, and zinc are grown for domestic comsumption or mined for export. Topographic and geological maps of a 1:500,000 scale are available.

A free-wheeling socialist country, Madagascar was annex by France in 1896, gaining back its freedom in 1960. The first parks were set aside in 1927 and are fairly numerous, but small. Many, like the pinnacle karst of the Tsingy National Reserve of Bemaraha, are only accessable by scientists studying the natural history, else they be stripped of wood and trampled by cattle. A fair road system winds along the east coast with a few feelers crossing the island, but travel is difficult. Ecotourism is being seriously considered as a partial panicia for the impoverished nation as the island is famous for its lemurs. Hot springs, the karst "sunken" forest, and pockets of surviving tropical rain forest with large colonies of flying foxes are also candidates for measured development.

Suggested readings include:

  1. Raymond Furon's 1963 book, Geology of Africa published by the French National Museum of Natural History and also available in English from Oliver & Boyd, London;
  2. a 1975 article by Jan Kutina in the Geol. Society of America Bulletin on the Tectonic and Metallogeny of Madagascar;
  3. and several National Geographic Society articles such as:

Mark Minton, from Cavers Digest 5437, topic 20

I certainly wouldn't characterize the caves of Madagascar as short. The five longest are 18.1, 12.0, 10.8, 10.5, and 9.0 km long. The deepest is 200 m deep with a very nice 165-m entrance pitch to a large room. Most of these are relatively incompletely explored. Only those caves in the far north are particularly wet or present any crocodile danger, although the very possiblity did keep me on guard whenever I rappelled into a pit or waded into a stream up there! I never saw a croc underground (I was slightly too far south), but did find scales in the sand of some of the larger passages.

Mark Minton, from Cavers Digest 5439, topic 1

>Fossil skeletons of lemurs have also been washed into these caves.

While it is undoubtedly true that some lemur fossils get washed into the caves of Madagascar, most of the bones seem to be there because that is where the animal died. Even today, lemurs go into the caves for water (I've seen this personally) and possibly for shelter from predators. The caves make excellent collecting sites because the bones are often quite well preserved and just lying there visible on the surface, even for bones that are thousands of years old.

>Topographic and geological maps of a 1:500,000 scale are available.

More detailed topo maps (1:50,000 ?) are also available in the capital (Antananarivo), although somewhat difficult to obtain. Many are out of print, although sometimes xerographic copies can be had.

Updated a one year later:

Justin Moat from Royal Botanic Garden, Kew (UK) published on WWW a paper MADAGASCAR: Vegetation Mapping and Biodiversity Conservation (using Geographical Information Systems) which among other presents map of simplified geology of Madagascar.

He stated: This map was digitized from the geology map of Madagascar (BESAIRIE, 1964). The 96 original categories were reclassified into predominant rock types which seem to have an important effect on the vegetation they support. The categories of sedimentary rocks include sandstones, loose (unconsolidated) sands, and two limestone categories of different ages (one of which produces the spectacular "tsingy" areas of jagged, highly eroded limestone pinnacles). A broad category of metamorphic rocks (including granites and migmatites), often covered by thick layers of laterites, covers large areas of the central and eastern areas of the island. Lavas and basalts, and several restricted rock types including quartzites, marbles and ultrabasics are also distinguished.

Below his map:

NOTE: The two kinds of blue signatures:
a) Tertiary limestones + marls & chalks and
b) Mesosoic limestones + marls (inc. 'Tsingy')
are potential karst areas.

Click on map for very large image (1655x2340 pixels, 142Kb).

Topography from Madagascar Biodiversity and Conservation

Geological history from Malagasy/Indo-Australo-Malesian phytogeographic connections

Related links:

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Last Updated: October 31, 1998