February - 2019

Mulu Caves 2013 was the 21st Anglo-Sarawak Expedition to Gunung Mulu National Park and operated in the field between 8th and 31st October 2103.  The expedition based itself at Camp 5 in the Melinau Gorge, with a satellite camp near the Medalam River, north of Gunung Benarat, for part of the time. The team was led by Mark Brown and comprised seventeen members from the UK, Australia, Denmark and our hosts at Sarawak Forestry.  The expedition was further assisted by National Park Management, staff and local people. The expedition had a mixture of scientific and exploration objectives which were successfully completed.
Whiterock River Passage, Mulu

In the Whiterock River passage | photo: Jeff Wade

Marvellous Science

The geological study focused on the progressive mechanical modification of the dissolutional cave passages in Whiterock Cave.  Preliminary examination of the prior survey suggested that high level passages such as Big Issue and the Northern Line were highly modified by breakdown, whilst lower passages such as Daydream Believer were less so.  In the cave a sequence of passages at different elevations were visited and their morphology, structural control and mechanical modification were recorded.

This remained stable in massive beds, but was modified by unravelling (block loss) in areas of high joint frequency.The geological control on cave passage form was found to be complex with a variety of joints, paleokarst fractures, crackle breccias and shear zones being important rather than simply the dip and strike of the beds. The relative elevation of the phreatic or paragenetic tube passage roof and the through-cutting notch associated with gravel transport through the cave was also important in controlling the extent of breakdown.   Passages tended to evolve with initial loss of roof and hanging wall blocks to a sloping bedding roof. Thereafter there was a change to an arched form. This remained stable in massive beds, but was modified by unravelling (block loss) in areas of high joint frequency.

The latter can also be seen in Api Chamber, where the first (northern) part of the chamber is dominated by shedding of huge wall parallel sheets, and the second higher part of the chamber by unravelling forming a high dome with much smaller breakdown. It is clear that upward stoping of the chamber from an elevation below that of Daydream Believer has intersected and consumed the Janet’s Way paragenetic canyon. Samples to define the timing of breakdown in the chamber were collected for Uranium Series analysis.

Fourteen guano crust samples were also collected to extend the collection from the Southern Hills.

Exploration, Surveying and Photography

Teams followed up leads from previous expeditions, exploring, surveying and photographing a significant number of new passages in existing caves and locating some new entrances from surface searching. In total the expedition surveyed 8660m of new passages. The survey work was carried out in a very accurate and detailed manner, as numerous connections and loops from known passages were found. Some use was made of the digital DistoX devices and “in cave” drawing on a Personal Digital Assistant device via “Pocket topo” software.

Most of the newly explored and surveyed passage was in Whiterock Cave, part of the Clearwater system in Gunung Api. The total added to Whiterock was 7947.44m*, which has increased the total length of the Clearwater system to 197.077km – moving it up from 10th to 9th place in the ranking of the world’s longest caves.

The other main cave explored was Deliverance in the Northern end of Gunung Benarat. 596m were surveyed in this cave, including a bolt climb of 103m vertically.

Whiterock Cave, Gunung Api (part of the Clearwater System)

The extensive length of Whiterock Cave meant exploration has been split into three main areas:

  • The North
  • Central area
  • The South.

The North

The postulated northern entrance to the system from the Melinau Gorge has not been found from inside the cave system or outside (see Doline sink later). Numerous underground passages in the area of the Melinau gorge ended in chokes of boulders, some of these were sandstone in the alluvial sediments below the aggrading Melinau river level. Teams camped at the “Flying Monkey” underground camp to explore the northern area. Inlets and climbs into side passages from the Whiterock River passage were surveyed to a conclusion, including Swiftwater Inlet and Cascade Inlet. The most significant side passage Midnight Express was surveyed for 717m.

cascade inlet, whiterock cave, mulu

The Cascade Inlet to the Whiterock River | photo: Jeff Wade

Central Area

A pitch in Out of Africa led to an extensive series of passages, well decorated chambers and a streamway in the lower levels. Camping in the Africa part of the cave provided access to this area, which was named the Exodus Series. A total of 3540m was surveyed in Exodus.

Exodus Series, Whiterock Cave, Mulu

A passage in the Exodus series | photo: Tony White

The South

A team went down to Api Chamber, camping at “Hotel California” underground camp, to study the formation and geomorphology of the chamber and passages en route. An investigation into the Firecracker passage of Blackrock Cave was carried out, which identified some possible climbs into new territory for a future expedition. A pitch and a side passage off Big Issue were explored, which both led into a large main passage heading north/south – Chance Encounter was surveyed for 500m. This passage continues to the south as a lead for a future expedition.

Highland passage , Whiterock Cave, Mulu

Highland Passage at the choke up to Api Chamber | photo: Andy Eavis

Deliverance – North Gunung Benarat

This cave in the northern tip of Gunung Benarat had been surveyed by the American expeditions in 1997 and 2000. A number of leads remained, and the cave looked good for possible continuations to the south, being on the same geological bed and altitude as some caves in the south of Benarat.

A low impact satellite camp was established close to the cave, near the banks of the Medalam River, in order to access this cave.

forest camp near Deliverance, Mulu

Forest camp near the Medalam River | photo: Jeff Wade

Most of the leads left by the Americans were climbs requiring “aid climbing” techniques, using bolts in holes made by battery drills. The hoped for continuation to the south did not materialize and the biggest shaft above Civet Hall was climbed for a further 103m, where it is still continuing up, but time and resources prevented further progress. Only short sections of horizontal passage were found off the main shaft. Other leads in the cave were short loops back into the main cave or ended in collapse chokes.

Red Tip Racer Cave (Melinau Gorge south side)

The location of this cave is interesting as it is much further east than any of currently known Whiterock and the geomorphology is very similar to Tiger Cave and parts of Whiterock – a large passage with lots of alluvial fill, detached wall flakes and corroded calcite. A bolt climb from the previous expedition was completed in the cave to reveal a passage 12.4m up, which was completely blocked by calcite. However, a possible high level lead remains in the large passage near the entrance.

Surface Searching

Helicopter flight

A helicopter flight was organized by Andy Eavis with Liang Liang Helicopters, through Richard Hi of Tropical Adventure. This transported some bridge making equipment to Camp 5 for the National Park and gave all the team members a “fly around” to see various areas of Gunungs Api, Benarat and Buda and the Deer Cave Massif from the air. The National Park manager and wife were given a fly around as well. The flight showed several features of speleological interest for investigation by future expeditions.

cave entrance, Mulu

A large entrance on the lower slopes of Gunung Api | photo: Andy Eavis

Doline sink (Melinau gorge south side)

Doline sink on the surface was explored and some rocks removed to make downward progress that was tantalising, but with no breakthrough. The survey showed that the lowest point of Doline sink is still 30m higher and 230m horizontally away from any known parts of the Whiterock Cave.

Gawai Doline (North G. Benarat area)

Recent expeditions have searched for the entrance to the Gawai Cave, explored by the Japanese team in 1997 (for which no survey has been drawn up). The doline reached by the 2011 team (and thought to be the location of the Gawai Cave) was explored during the 2013 expedition. A cave entrance was found, but it is thought to be a high window into “The Casting Vote” passage of Blue Moonlight Bay Cave. The helicopter flight identified another potential entrance feature further east, but the team was unable to reach it during the expedition.

Half Moon Penguin Cave (G. Benarat cliff, Melinau gorge)

An airy abseil was rigged down the full 300m height of the Benarat cliff, in order to access this cave entrance visible at half height in the cliff. The cave was blocked after 30m and thought to be associated with part of the Benarat Caverns system. The name is derived from a radio communication from the team, describing how they were “huddled like penguins” in the entrance, whilst a thunderstorm raged during the descent.

Other sites

A cave entrance was reached high on the northern flank of G. Benarat (circa.500m altitude), which is an interesting feature for a future expedition.


The expedition has explored and accurately surveyed numerous cave passages in the complex Whiterock Cave, to extend the Clearwater system and move it up in the world rankings. Deliverance cave has been extended with no major ways on discovered, but with one of the tallest underground aid climbs yet undertaken in Mulu. The utility of a satellite forest camp to access this remote cave has been proven.

The scientific work will continue to provide new information on the geomorphology and ages of the caves, past climate reconstruction, and geochemistry of the sediments.

The team identified and recorded a good number of underground and surface leads for future expeditions to continue with.


From Sarawak:

The Chief Minister of Sarawak
The Sarawak State Secretary
The Director of Forests, Sarawak
Protected Areas & Biodiversity Conservation Unit, Sarawak Forestry Corporation
Gunung Mulu National Park Management & Staff
Local organisers and assistants
Oswald Braken Tisen
Rambli Ahmad
Veno Enar
Richard Hi (Tropical Adventure)

The expedition is very grateful for the support of the following sponsors and organisations:

Ghar Parau Foundation
Leica Geosystems Ltd
Makita (UK) Ltd
Mark Wright Training Ltd
Andy Eavis

A full list of acknowledgements will be published in the final report