Karst is an area with a topography characterized by mostly limestone, with crevices, wholes and caves that were formed by the dissolution of a layer of soluble bedrock by rainwater or the water from rivers. Rainwater, as soon as it falls on the soil, immediately seeps into the ground leaving behind a dry surface. Karl Helbig was the first scholar to write an article on the Karst Cone Landscape so typical of Nusa Penida in 1941.
In the tropics there are different kinds of karst landscapes. One of these karst zones was formed by a limestone 'ridge' in the ocean south of Java and Bali during the Pleistocene some 70 million years ago. Layers of seafloor were pushed up from the south towards the north over a large distance. The result today is called Tertiary Karst an extends from Gunung Sewu to Blambangan in south Java, Bukit - the southern peninsula that once was another Karst island - Nusa Penida, Serangan island (now a peninsula) and the entire south coast of Lombok.
Image above: cone-shaped karst landscape typical for Nusa Penida higlands (FNPF, 2010)
The Karst landscape of Nusa Penida is called Cone Karst as the interior of the island is covered with cone-shaped hills. As is the case in other Karst zones, here too, rainwater has little chance of fertilizing the soil as it drains into the bottom away almost immediately. Nusa Penida has three layers of Karst. Firstly there is the youngest layer at sea level, then there is a second layer to be found at approximately 220 metres altitude and the oldest layer can be found at 450-500 metres altitude. On the south coast the second layer drops vertically into the ocean and sometimes runs the risk of collapsing because of many years of erosion by seawater. There are similarities between the karst topography of Nusa Penida and Bukit (South Bali, called 'Tafelhoek' or 'Varkenshoek' by the Dutch during the colonial period). Nusa Penida is twice the size of Bukit, and consists of limestone layers three times as thick as those of Bukit with a highest elevation of 167 meters.
In contrast to the area of Gunung Sewu on Java, on Nusa Penida there is no red soil (Terra Rossa) or lava rock to be found, unless it is imported from elsewhere. Similarly, there are no lakes ('Telaga') as there are in Gunung Sewu. But fortunately, on top of the limestone layers there is a (thin) layer of fertile, black soil that consists of limestone gravel mixed with animal dung and vegetable mould.
- Helbig, Karl (1903-1991) - Nusa Penida, eine tropische Karstinsel; In: Mitteilungen der Geographischen Gesellschaft in Hamburg, Band 47, no.25 (1941), p.393-409
- http://en.wikipedia.org/wiki/Karst_topography (viewed 1 December 2012)