March - 2019

Since its discovery in 1980, Sarawak Chamber has long been regarded as the largest natural underground chamber in the world. But with recent new discoveries of large chambers in other parts of the world, Sarawak Chamber suddenly had competition. Clearly an accurate measurement was required, and in 2011 advanced laser measuring equipment was used to calculate the true size of Sarawak Chamber. Is it still the world’s largest?…… Kevin Dixon reveals:

Sarawak Chamber was discovered in 1980 by Andy Eavis, Dave Checkley and Tony White during the Mulu ‘80 expedition which was a follow up to the 1977-78 Royal Geographical Society Mulu expedition.

In February 2011, the Anglo-Malaysian Mulu Caves Project expedition set out for Sarawak Chamber with a 3D Laser Scanner and a team prepared to camp underground for several days. Laser scanners have been used to model caves before, such as England’s Gaping Gill, but it was not known whether they would have sufficient range for the large caves and high humidity of Mulu. The team were therefore taking a big risk with an expensive and relatively delicate instrument.

Heavy rain the previous evening had swollen the rivers, making for some challenging river crossings to reach the cave entrance after traversing 8kms of the Borneo jungle. Normally, the cave entrance passage has knee deep water but overnight flooding required the team to swim against the current with the equipment tied onto an inner tube and log raft. The water current proved too swift for the raft, progress could only be made by one team member swimming along the passage side with a rope, anchoring themselves to the wall and then pulling the raft upstream. The other team members keeping the raft off the wall with their feet whilst trying to avoid limestone pinnacles sticking up from the passage floor hidden below within the swirling waters.

After 400m of hard going, the ten strong team were finally able to touch the passage floor and then had to backpack the equipment another 700m along the streamway, traversing round the side of the plunge pool, climbing over the high level ledge traverse before clambering over the car sized boulders at the start of the slope up to Sarawak Chamber. The campsite had sufficient room for the three laser scanning team members, Kevin Dixon and Meg Stark from York plus Andy Eavis from Hessle to set out their sleeping mats and a cooking area. The seven strong support team set down their loads, bid their farewells and set off back to the surface for the long trip back to the National Park Headquarters.

Sarawak Chamber laser scanning

Kevin Dixon monitors the laser scanner in Sarawak Chamber | photo Robbie Shone

Having set up camp, the 10kg laser scanner, 3kg tripod and 5kg battery were backpacked to the centre of the Chamber where it was set up on the edge of a house sized boulder to do the first overnight laser scan. Traversing the chamber involves climbing moving scree slopes in high heat and humidity – very thirsty work. The Scurion 1300 headlamps were able to throw their light immense distances in the chamber and helped point the way but their brightness drew in clouds of flies and these would often be breathed in causing a bout of coughing/retching which would give the recipient time to think about what the flies usual diet in the cave – Cave Swiftlet guano. The team returned to camp for their first candle-lit meal with the background sound of dripping water and the constant clicking of echo-locating Cave Swiftlets flying to their nests on the walls and ceiling of the cave.

There was no dawn to greet the team in the morning, only the light from two candles to prepare breakfast and get ready for the day ahead. The laser scanner had been successfully tested in Deer Cave a few days ago but whether it would fully function within the heat and humidity of Sarawak Chamber was unknown. The morning was very misty as the team made their way back to the first scan station, an ominous sign because mist can absorb the laser energy and so prevent long range measurements. The battery had died overnight and the laser scanner was covered in condensation, both were not good signs. A laptop had been taken into the chamber to check the data and the first laser scan was anxiously downloaded. Fortunately it had worked well with a maximum range of 605m measured. The scanner was moved to a new site and the second of four batteries was started, taking care to measure the voltage periodically to assess it’s performance. Early failure of the batteries would require a lengthy trip back to the Park headquarters for replacements.

The team spent four days and three nights in the chamber. A hand held, 1.5mm accurate, Leica Geosystems Disto D8 laser range finder was used to check the distances between the scanner stations. The laser scanner measured a total of 12.9million points with an accuracy of 10-20cm. Each scan was assessed on the laptop whilst in the cave because there was the possibility that the laser might reveal new cave passages in the roof. The four batteries had lasted for the survey duration but only just. Having weather underground was a novelty for the team, the mist would steadily clear during the day only to return the next morning and although later analysis showed a dimunition of laser range, it did not significantly effect the survey. The support team came back as pre-arranged to help carry out the equipment and assist the tired laser scanning team back to daylight. Water levels had receded and the cave entrance passage which had been a raging torrent on the way in was now low enough to permit a relaxed walk out.


Upon return to the United Kingdom, the data was collated and processed at length by York based Geospatial3D into a virtual 3D cave model. Analysis of the model has revealed the following:

Sarawak Chamber measurements

Sarawak Chamber measurements

Only the Everett building used by Boeing to assemble their largest jets in Washington state, USA has a bigger usable volume (13.3million m3) than Sarawak Chamber. However Everett has internal columns to support it’s roof whereas Sarawak Chamber has a clear span. A circle of 325m diameter can be fitted into the floor plan of Sarawak Chamber, this is larger than the largest unsupported man-made dome structure of 275m diameter for the Dallas Cowboys Stadium. The O2 arena in London has an internal diameter of 320m but is supported by internal pylons. The chamber features two domes in the limestone ceiling with high spots of 115m and 105m above the chamber floor. The multi-domed ceiling, the angle of the chamber floor at the interface between the underlying sandstone strata and the overlying massively bedded Mulu limestone may help to explain how such a massive chamber can exist. The river runs from north to south west and is hidden from view by a massive pile of limestone boulders at the base of the chamber. The chamber is 300m higher in the east where the underlying sandstone strata appears.

To put the tremendous size of Sarawak Chamber into context, it can be compared with the following man-made structures:

Sarawak Chamber and manmade buildings

Man-made buildings compared to Sarawak Chamber

A false colour composite of the virtual model of Sarawak Chamber, as seen from the south west, highlights an 800m length of the geological fault at the base of the chamber along which the underground river has developed:

Sarawak Chamber scan model

False colour composite view from south-west

A second view shows the chamber from the south east and below and illustrates the central ridge running through the chamber:

Sarawak Chamber scan model south east

Sarawak Chamber scan model from south east

Is Sarawak Chamber the biggest undergound cave chamber in the world? A new analysis of the cave survey for Salle de Miaos, in China, which although passage-like, has long been listed as the second largest natural underground chamber has produced a volume of 7,060,374m3 and area of 117,765m2. The next largest underground chamber, Cloud Ladder Hall in China has a volume of 5,846,973m3 and area of 51,158m2. Given the above, Sarawak Chamber, with its volume of 9,579,205m3 and area of 164,459m2 is currently the world’s largest natural underground chamber.


At the British Caving Association annual conference held in Monmouth September 2011, the British Cave Research Assocation awarded the annual Arthur Butcher prize to the Mulu 3D Laser scanning team for excellence in Cave Surveying.