March - 2019

Both the Gunung Mulu National Park and respected international cavers have described the giant caves of Mulu as the largest caves in the world.  However, contenders for this title can be based on several different conceptions.  The largest means the greatest in size of those under consideration but what ‘size’ do we consider.  There is the longest, the deepest, the largest chamber, the largest single passage and the greatest volume but none of these alone can describe the largest caves in the world.  To do this we need to look at a well defined geographical area and take a balanced view on all the ‘largeness’ that the area has to offer.


Insomnia, Whiterock Cave. Photo © Robbie Shone

The caves that lie within the limestones of G. Api, G. Benerat and the Southern Hills are within a well defined historical and geographical area.   However, the conditions have to be favourable for large caves to develop and Mulu has the required conditions in abundance.  Perhaps the most important is rainfall and Mulu records average annual rainfall figures of 5700mm.  High rainfall gives rapid run off into the limestone fissures and ensures solution potential is not exhausted near the surface.  However, much of the solution occurs from surface rivers flowing off the Mulu sandstones.  These rivers have very high erosive capacities, as shown by limestone tablet weight loss experiments.  The high solution rates combined with the strength of the local limestone enable the development of very big caves.  The Melinau Limestone is very pure, dense, fine grained and exceptionally massive, with widely spaced beddings and joints (Smart 1984). Water movement is concentrated into a limited number of favourable paths, which guide passages for long distances and erode to large sizes.  The Melinau limestone is mechanically strong too, allowing huge roof spans to occur, such as the massive Sarawak and Api Chambers. 

High traverse in Hurricane Hole. Photo © Robbie Shone

Mulu is also remarkable for the high density of passages in a relatively small block of limestone.  At the southern end of the Clearwater system, in a large area spanning an elevation range of 300m, at least 3% of this is void.  This density and average passage size demonstrate a continuity of cave development over a considerable time span. Scientific research to date this process has been ongoing for many years and continues with the latest expeditions.  Indications are that the caves have been developing for several million years at least.

Upper Borderline, Whiterock Cave. Photo © Robbie Shone

The Geographical definition and the Geomorphological condition are clearly in Mulu’s favour.  So are many of the conceptions of largeness.   Mulu has one of the ten longest caves in the world and the Clearwater System is probably the largest cave by volume too.  It has the largest underground chamber and one of, if not, the largest single cave passage in the world.  The Mulu caves do not have great depth but do have a wealth of other massive karst features including the Garden of Eden and the Pinnacles.

Taken together we can conclude that there is enough evidence to support the claim that the largest caves in the world lie within the Gunung Mulu National Park.  Mulu has the largest chamber, possibly the largest cave by volume, one of the largest passages, a top ten longest cave and a number of other mighty karst features, all within a defined area that the National Park has made accessible to the public.  Where else in the world are so many large features so visible and so accessible?  The answer is nowhere.

Api Chamber, the Clearwater System. Photo © Robbie Shone