Karren and Formation of Caves and Their Relationship to the Bemaraha Tsingy, Madagascar

The most significant geomorphological charactersitic of the Bemaraha Tsingy (Madagascar) area is its karst topography characterized by grikes and caves. The origin of these structures has been disputed for the last few decades [1,2]. By means of the geomorphological field observations and size calculations of grikes as well as karst water current measuerements, here we show that caves could be formed in grikes, slides of grikes and in between grikes. Grikes were formed along the lithological joints representing two directions such as NNE-SSW and WNW-ESE. The scallop system indicates that water flow occurred in grikes. It was calculated that the karst water current was varied between 5,560 and 159 cm/s. According to the cross section parameters, grikes should be divided into two groups as simple (dominated by down-norrowing or vertically sliding slopes) and complex (abundant and characterized by relatively wide bottom) grikes. In conclusion, according to the above-mentioned observations and calculations, grikes were formed from caves following their roof breakdown occurred by collapsing roof or simultaneously they were connected to surficial rain water solutions. Natural bridges of Tsingy are remnants of the caves. It is evidently shown that primer cave system of this area was formed by the streaming water processes indicating that the previous erosional level was as same as at the Manambolo river, recently. For instance, river-related sand deposits were found in some grikes and caves.

References: [1]. Middleton, G. (2004) Madagascar.-In: Gunn, J (ed.): Encyclopedia of caves and Karst Sciencia, Taylor and Francis Books, New York, p. 493-495. [2]. Ford, D.C. and Williams, P.W. (2007) Karst Hidrogeology and Geomorphology. John Wiley and Sons Ltd., 561 p.