The formation of Mulu
More than 40 million years ago, this area was part of a deep sea, in which a great thickness of clay and sand were deposited, eventually forming shale and sandstone. Formation of limestone (an expanse of rock known as the Melinau limestone formation) commenced some 40 million years ago as the sea became shallower and clearer, enabling growth of coral. Corals reefs flourished over an estimated 20 millions years. This coral became limestone, and is very thick - 1500m in parts.
Between 10-2 million years ago, both the limestone formation and the sedimentary seabed were pushed upwards, forming the mountain ranges that are now Gunung Api, Benarat , Buda, and Mulu. A vast quantity of shale and limestone was sloughed off Gunung Mulu, exposing sandstone and more shale. The sea receded and rivers cut channels through this uplift, forming valleys between the mountains.
Rivers swept out silt and created the alluvial flood plain on which the Park HQ is situated. Water continues to shape the park slowly but forcefully. Mulu averages a torrential amount of rain - between 4482-6802mm each year. The caves, the Pinnacles, canyons and cliffs are all a result of water erosion - the slightly acidic, torrential rain in tropical warmth dissolves calcium carbonate from limestone.
Over millions of years, rain and rivers have eroded and redistributed debris from these limestone mountains. Mulu’s caves are formed as water percolates through cracks and faults in the limestone, dissolving soluble calcium carbonate. The effects of water can be dramatically different depending on flow, volume and limestone composition. In Clearwater Cave, kilometres of sinuous smooth-walled caverns are sculpted by an underground river. In Deer Cave and the Sarawak Chamber the hard, stable quality of the limestone, together with buckets of rain and tropical warmth allowed the development of the huge chambers found today. In King’s Chamber, the slow dripping of calcium carbonate-saturated water results in the imperceptible growth of stalactites and stalacmites.
For those fascinated by world records, many of these caves are title holders:
- Clearwater Cave is the world’s longest system of cave passages (over 107km explored to date);
- Deer Cave, easily accessible to tourists, is the world’s largest cave passage (2km long, 174m wide, 122m high); and last but by no means least
- the Sarawak Chamber is the world’s largest underground cave chamber, measuring approximately 400m x 600m, big enough to house numerous jumbo-jets, or football fields, depending on your preference for comparison.
Mulu National Park is a paradise for cavers - and a challenge - as many parts of its underground labyrinth are still unexplored.
The mountains and the Pinnacles
Because of the soluble calcium carbonate content of limestone, it is much more susceptible to water erosion than sandstone and shale. The limestone mountains of Gunung Api (1750m), Benarat (1585m) and Buda (963m) were once the same height as the sandstone Gunung Mulu (2376m), but these have all been eroded at a faster rate. The Pinnacles are a spectacular example of limestone erosion.
The Pinnacles have now come to symbolise Mulu National Park. From 1200m altitude on Gunung Api’s flanks, these giant knife-like formations reach heights of 45m, and are a great illustration of the ruggedness of limestone terrain. Without any soil cover, limestone is very susceptible to erosion by rain. The Pinnacles were formed by water pooling and trickling into vertical fractures in the limestone, which widen and deepen into crevices. The harder blocks of limestone between these crevices remain, elongating like teeth (or fangs!) set in receding gums. The Pinnacles continue to be sculpted by the dissolving force of rain, developing sheer, knife-like edges.
Navigating through this nest of knives posed great challenges to the exploration of Mulu.
The 19th century explorers Hugh Low and Spenser St John (of Kinabalu fame) tried to climb Gunung Mulu, approaching Gunung Api first. Here’s a description of the encounter by St John:
“In Feb 1858, Mr Low and I again attempted ascent of Molu….We could find no water except such as could be obtained from squeezing the moss, or from the pitchers of 2 new kinds of Nepenthes. ….We worked our way over the most dangerous places, where a false step would have broken our necks or limbs, or have us cut to pieces on the sharp rocks; as we advanced, precipices and deep fissures became more frequent, one of the latter we crossed on a tree only 4 inches in diameter which was felled for the purpose. It bent beneath us ….I was thankful to have passed it, as the chasm below was filled with jagged rocks. The Malay description of it is true ‘sharp axes below and pointed needles above, such are the mountains of Molu.’ ”
Gunung Api was first successfully climbed in only in 1978.
Gunung Benarat, across the Melinau River from Camp 5, remains unclimbed. Rising up from the river valley as sheer white cliffs capped by ridges of lush green rainforest, it has an intimidating, fortress-like quality.
In contrast, Gunung Mulu with it’s shale and sandstone base, is less treacherous terrain. For much of Sarawak’s colonial past, it was believed to be Sarawak’s tallest mountain (Gunung Murud, in the Bario highlands is in fact slightly taller at 2432m), and attracted several explorers from the 19th century onwards. Spenser St John and Hugh Low (quoted above) made two unsuccessful attempts to climb it, followed later by Charles Hose, who also failed.
Tama Nilong, a local Berawan, came close to the summit Gunung Mulu in the 1920s, discovering a route up it while hunting an injured rhinoceros. As pursuit of rhinoceros was the purpose of this excursion, when the animal fell down a hillside, Tama Nilong followed it - getting thoroughly lost in the process. He survived 13 days without food and eventually made it home.
In 1932 the young Edward Shackleton (son of the famous Antarctic explorer), with Tama Nilong as his guide, finally summitted Gunung Mulu for the first time. Lord Shackleton was part of a brash group of young men (with an average age of 20) on an Oxford University Expedition headed by Tom Harrisson (who would go on to become an important figure in Sarawak’s pre-Independence history). The brazenness of a cocky young man from England bagging the “tallest mountain” in Sarawak and upstaging old Borneo hands caused much consternation amongst Sarawak’s conservative colonial officers.
The rivers in Mulu National Park sculpt its surface and interior as well as forming its boundaries. Some of these watercourses are scenic attractions in themselves clear, clean and full of fish qualities rarely found in South East Asian watercourses. The Sungai Melinau is the main river on the park’s western side, and its only means of access prior to the airport being built. It flows into the Sungai Tutoh, which forms the southern boundary of the park. The Sungai Medalam and Mentawai are the major rivers in the north of the park.
As well as shaping the landscape, rivers are fundamental in maintaining soils, plants, animal and human life in and around the park. The rivers of Mulu support a rich variety of fish life. Brood stock collected from these rivers in the 1960s formed the basis for aquaculture in Sarawak. Fish were so abundant during this time that they were caught simply by clubbing the water.
Riverine forest, with its variety of soils, contains many ecologically important plants, such as fig trees which play a key role as a food source for many of the park’s animals.
The indigenous inhabitants of Mulu have always been aware of the importance of the rivers. For the Orang Ulu, longhouses were and continue to be built along riverbanks. Prior to logging roads, rivers were the highways of the Borneo interior navigable by shallow bottomed longboats, a source of food, and a means of accessing jungle for hunting. For the nomadic Penan, rivers were their maps to navigate and recognise their land, first and foremost, they had to know the rivers.