Karst in Southeast Asia

Flying over the patchwork quilt of land uses that comprise Southeast Asia, one often sees extensive tracts of rugged topography with plateaux pitted with depressions, deep gorges, rivers arising at the bases of mountains, and towers arising from alluviated plains. These are the karst lands, formed on limestone bedrock and subject to the solutional erosion of that bedrock above and below ground. With a total area of about 400 000 km2, Southeast Asia contains some of the more extensive karst regions in the world. Many of these karst areas are of high relief with spectacular arrays of tower and cone karst. Many have now been inscribed on the World Heritage list in recognition of their unique geomorphology and biology. They are scattered throughout the islands of the Malay archipelago as well as the adjoining fringe of the Asian mainland. Karst is found in Malaysia, the Philippines, Thailand, Brunei, Indonesia, Cambodia, Viet Nam, Lao PDR, and Papua New Guinea. Geologically the carbonate rocks hosting karst range in age from Cambrian to Quaternary, a span of about 500 million years (Letouzey, Sage, and Muller 1988). Over that time limestone solution and other landscape processes have produced an array of karst landforms including towers, cones, plateaux, and dolines, underlain by extensive cave systems. There have also been strong external influences of tectonism, eustatic, and climatic change. Today human modification of karst processes and landforms is proceeding at a rapid pace. Despite their characterization as the ‘botanical hothouse extreme’ (Jennings 1985) the karstlands of Southeast Asia are most diverse, reflecting the influence of varied geology, uplift history, eustatic change, and climates past and present. Karst landscapes range in elevation from sea level to nearly 4000 m, and comprise extensive plateaux with dolines, tower karst, cone karst, and lowlying swampy terrain. The carbonate rocks on which they have formed range widely in age, and can be soft and impure or hard and crystalline. Many areas have been wholly or partially blanketed by volcanic ash during their evolution.