Mulu Caves 1991

During October 1991 a group of six explorers and three scientists visited the Park to continue the exploration and geomorphological study of the complex system of caves within Gunung Api. Working closely with local guides and porters 8.5km of cave passages were explored and surveyed. A passage in Blackrock Cave was explored which after 600m led into Clearwater Cave's West Passage thus linking the two systems and establishing the Clearwater system as the 7th longest in the world, with a total length of 102km.

Geomorphological research centred on the collection of mud samples for paleomagnetic analysis and over 40 sites were studied between the resurgence and the 400m horizon.