General Information
The Gunung Mulu National Park contains some of the largest, most significant, and spectacular caves in the world, including one of the worlds longest cave system, the 151km long Clearwater-Blackrock-Whiterock system; the worlds biggest chamber, Sarawak Chamber with a void space equivalent to 162,700 square metres, the largest cave passage, Deer Cave, with its population of several million wrinkle-lipped bats, not to mention some of the finest tropical karst landscapes in Southeast Asia.
Geology of the Gunung Mulu National Park
The geology of the area is crucial to understanding why the Gunung Mulu National Park is so special. The rocks consist of a sequence of sandstones, limestones and shales which lie on the western side of a large anticline or upfold (the 'Mulu uplift’ or dome), so the rocks dip steeply at between 40° and 70° to the north-west. Three main rock units can be identified. In order of deposition, these units are the Mulu Formation, the Melinau Limestone and the Setap Shales Formation.
The oldest rocks in the National Park belong to the Mulu Formation, a series of coarse sandstone and shales, 5-6 km thick of Late Cretaceous to Eocene age (c. 40- 60 million years old), which forms the high ground of Gunung Mulu. The sandstones form very steep 'V' shaped valleys separated by narrow ridges which culminate in the summit of Gunung Mulu at an elevation of 2377 m. Landslides, usually in the form of long narrow ribbon slides, are common on the steep slopes and often occur during heavy rain.
Above the Mulu Formation there's the Melinau Limestone Formation. This unit consists of a 2.1 km thick sequence of massively bedded, strong, pale grey limestones of Upper Eocene-Lower Miocene age. These were laid down in a shallow sea between 20 and 40 million years ago. Because of the steep dip to the west (at around 60-70°), the Melinau Limestone now outcrops to the west of Gunung Mulu, forming a narrow, lenticular outcrop culminating in Gunung Api. The limestone also underlies the alluvial plain to the west where occasional steep sided limestone towers (batus) project through the alluvium.
Overlying the Melinau Limestone is the Setap Shale Formation, which consists of a sequence of mudstones with occasional marly bands and thin sandstone beds. These rocks were lain down in deeper water during the Middle Oligocene - Early Miocene period, some 20-30 million years ago. These outcrop to the west of the park, forming a small escarpment. Although generally younger that the other two rock units, the softer nature of these rocks means they have been preferentially eroded to form the low-lying area to the west of Gunung Api.
However, it is the Melinau Limestone which makes the Gunung Mulu area deservedly famous. As limestone is soluble, the action of water over time creates a ‘karst’ landscape, with many classic features peculiar to limestone terrains, including caves, disappearing rivers, sinkholes, springs and pinnacles. Four limestone massifs, from Gunung Buda and Gunung Benerat to the north, to Gunung Api (1692 m) and the Deer Cave Massif in the south dominate the landscape. These massifs rise steeply above the alluvial plains, often in sheer cliffs over 300 m high before levelling slightly to culminate in the summit. The surface is pockmarked with a dense network of closed depressions, collapse sinkholes, pinnacles and dry valleys, especially in the south of the Api massif. The limestone supports a very rugged, mature karst topography, riddled with some of the largest and most extensive cave systems in the world.
Clearwater Cave
Clearwater is the typical Mulu cave system on the grandest of scales - high energy active river levels and multi-layered relic cave above. This complex system has continued to reveal its secrets over 30 years of exploration and now, with Blackrock and Whiterock, comprises 151.4km of surveyed passage.
From the entrance, a boulder slope leads down to the river and to the left is the resurgence chamber which is fed by two rivers. The smaller of the two, Goldwater, picks up drainage from around the edge of the mountain to the north and is lightly coloured by tannins from fallen leaves. The bigger flow, from deep inside the mountain, is Clearwater, one of the biggest known underground rivers - in flood, 150,000 tonnes of water pour through the passage every hour. From this junction, the river passage continues for well over a kilometre, with impressive dimensions averaging up to 30 metres in diameter. For the explorers, this was very exciting caving as progression entailed crossing and re-crossing the river a number of times, avoiding razor-sharp blades of rock beneath the surface. Eventually the magnificent passage ends at River Junction, where it sumps. From here there is a network of passages bypassing the flooded area and leading to a massive complex of dry passages above. The biggest of these, Revival, bores its way north as a massive phreatic tube, with an average passage height of 45 metres and a width of 30 metres.
Over the years, continuing exploration of Clearwater has revealed a further 6 sections of the river, separated by sumps. The upstream limit of exploration, Clearwater 7, is extremely remote and the bypass to the last sump is highly flood-prone and can be closed off by high water for months on end. The active river sections are all linked into the multi-layered, dry cave passages above, forming a complex maze which spans a vertical range of 350 metres. In many of the high level relict passages there are huge banks of infill, providing evidence of previous phases in the cave's life when sediment has been forced into the cave under pressure from floods and landslides on the surface. Now these sediments block or impede exploration.
To the north of Revival, the Dune Series and Troll Chamber eventually link to the southern end of Blackrock and, close to the junction of the two systems, a tiny connection provides the ‘North Entrance’, a tight squeeze out to the surface which has only once been located from the outside, the entrance being an inconsequential rift between rocks, hidden in the forested hillside.
Midway along Revival, an ascent up a massive boulder slope leads to the Scumring, a pool of water or mud (depending on recent rainfall) from which two huge pitches are believed to lead down to the river far below; the second pitch has never yet been descended. The flat area around Scumring provided an excellent underground camp site and from here the 15km Armistice Series was explored another network of passages leading north at high-level to an end point only 800 metres from Whiterock's Api Chamber. The floors of many of the passages here are littered with the bones of dead bats maybe an indication that a collapse sealed off an old entrance, entombing the animals in the cave, or perhaps just the accumulation over thousands of years of individuals that were lost and died of thirst or starvation. At an even higher level, The Secret Garden, RMAF Hole and Solo are massive surface features on the mountain slopes and, of these, only the Secret Garden has a fully explored link to the passages below.
As well as the entrance at the resurgence and the tiny Northern Entrance at Troll Chamber, access into the system is possible at a number of other points along the foot of Gunung Api on the edge of the Melinau’s alluvial plain. The best known of these is Snake Track - its small beginnings exploding into the well-decorated grandeur of the north end of Revival. This entrance takes its name from polished tracks across the cave floor, highways for snakes, porcupines and rats entering and leaving the cave. Access into Clearwater 3 is also possible from the Melinau Paku Valley and, close by, a voice connection has been made between Drunken Forest Cave and Alexander Palace, a small, well-decorated chamber that was found during the exploration of Armistice and the river passage of Clearwater 5.
Logging requirements
Clearwater Cave is reached from the park headquarters (registration!) either by taking a fifteen minute trip up the Melinau River in a longboat or by hiking for an hour or more along a nature trail alongside the river.
To get log-permission please answer the following questions and send your answers to our GC-Account e-mail-address:
- How many tonnes of dissolved limestone are being carried by the river inside the cave every year?
- There are some light-oriented erosional pinnacles found in the lit zone of the cave entrance. What‘s the name of this phenomenon? Please give also a short definition of the developing process of the pinnacles.
Posting photos of your visit to the cave would be very nice, and is of course optional. Please don‘t log without our permission. We‘ll try to answer back very fast. Thank you very much.
refs: www.mulucaves.org