February - 2019

Mulu Caves 2014 was the 22nd Anglo-Sarawak Expedition to Gunung Mulu National Park and operated in the field between 13th April and 17th May 2014. Based at National Park headquarters, the team was led by Andy Eavis and included a total of twenty two cavers from the UK and Australia, together with a number of participants from our hosts at Sarawak Forestry. The expedition was further assisted by National Park Management, staff and local people.

The expedition continued its scientific programme, with studies of the genesis and geomorphology of the caves supported by collection of samples for analysis and uranium dating. The expedition also focused on exploration, mapping and diving objectives, with considerable success in all three departments.
During the course of the expedition the length of the Clearwater System surpassed 200 kilometres, promoting it to 8th longest cave in the world. And the discoveries made during the expedition suggest that Clearwater could easily climb further up the world rankings.

The 'Moai' formation, Easter Cave | photo © Chris Howes

Scientific programme

The expedition continued its scientific programme with further study of notable features which will help with understanding the formation of the Mulu caves. In places samples were collected for analysis and uranium series dating. (details of all samples collected are given in Table of Scientific Samples Mulu 2014).
The exposure of volcanic ash previously reported by Lundberg and McFarlane (2012) from Clay Hall, Cave of the Winds was visited. Samples of the ash horizon and the adjacent sediments were taken for analysis and the wider sedimentology of the deposit reviewed. Contrary to the suggestion of Lundberg and McFarlane (2012) that the deposit is due to back-flooding from the main cave stream, the deposit appears to be localised in a depression excavated in the much earlier cave fill of sands gravels and cap muds. It appears to have derived by inflow from the opening leading upwards from Clay Hall to Disillusion (Clearwater Cave) to a small lake formed in the depression. There is however no evidence of similar material in the Disillusion Passage which contains only the earlier fill. Paleoflow indicators show that the earlier fill was emplaced by flow upwards from Clay Hall into Disillusion.
The ash exposure is very limited and consideration should be given to its protection eg by taping off the outcrop, even though it is not widely visited. A second site with probable volcanic ash exposure was found in Clearwater Cave at the head of the Streamway. A short passage leads up from the Streamway opposite the entrance to the Battleship and terminates in a tube partially excavated through a white waxy fill very similar in nature to that in Cave of the Winds. Samples were collected. Very much higher in the new Credence level of Clearwater Cave, samples were collected of a waxy chocolate coloured deposit, which may also be ash derived.
Several cores were taken from guano in Deer Cave to determine rates of turnover and test for biomarker evolution. A small number of additional samples of guano crust were also collected to supplement those previously taken.

Allophane deposits in Clearwater Cave | photo © A.Farrant

Additional observations were made of mechanical failure of roof and walls in several of the larger cave passages and chambers. This included photographic documentation of features in Lagangs Cave, and observations in Disillusion, Clearwater Cave. Here two phase collapse is occurring, with an initially stable arch being destabilised by collapse of one wall into an underlying cave passage. In Nasib Bagus a survey of the northwest wall of Sarawak Chamber was made, and indicated that undercutting and failure was occurring as a result of erosion by the cave stream which lies under boulders along this wall. A topographic survey of the south east area of the chamber where mudstone-derived deposits are present was made. Over 1 km of survey lines were completed over difficult terrain. The walls of the chamber in the south east alcove are of Mulu Formation mudstones and are actively failing bringing in a mix of mudstone and large scale failed limestone debris. At the head of this zone to the east in the chamber is a failure surface comprising a steep wall of mudstone 15 -20 m high. At this point huge limestone slabs fall from the ceiling and accumulate in the debris at the base of the slip surface. Proceeding to the north the mudstone wall lowers and is replaced by a slope of failed mudstone debris. This extends down to the base of the slope above the trench excavated along the north west wall from which the debris is evacuated by overflow of the stream. Further to the north the mudstone debris is replaced by partially cemented limestone breccias with a mud matrix. These have failed giving a slip surface at the rear of the gulley they infill. Further north still large scale limestone blockfall dominates, but this area was not studied on this trip, nor was the area above the shale cliff. These remain key mapping objectives for any future visit.
Samples of stalactites broken during roof fall, and of stalamagmites growing on fallen limestone blocks were collected for uranium series dating at Bristol. Over much of the central area of the chamber the current inflows do not deposit speleothem. This is also the case in the highest parts of Api Chamber.

Cave Exploration

Southern Api
Early in the expedition a local guide directed the team to a new entrance 20 minutes above the (currently closed) boardwalk between Park Headquarters and Cave of the Winds. Easter Cave provided a feast of exploration in an area where many thought there was little room for additional cave passage, and much of it was on a grand scale with large fossil passages on several levels.
The cave was able to absorb a lot of manpower in exploring and surveying, and was still going strong when a late team arrived in Mulu from the UK. They brought with them some temporarily mislaid survey data which showed that some of the new cave had in fact been previously entered, representing the upper levels of Racer Cave explored during 1991. Undeterred, the team continued their high grade surveying, covering both new ground in Easter Cave and re-mapping in detail the former discoveries in Racer Cave. Over 4 kilometres of new cave were explored and surveyed, and 2.5 kilometres of known cave was re-surveyed. And considerable efforts were made, unsuccessful as yet, to force connections with the nearby Lagangs Cave and Cave of the Winds. However, many leads still remain to be followed, and there is a high level of optimism that Easter/Racer will connect with Lagangs Cave in due time.
In Lagangs Cave efforts were made to climb upwards in a variety of leads that might connect with the overlying Easter Cave/Racer Cave system. Although a connection was not attained on this occasion, an additional 1.5 kilometres of passages were explored and surveyed in the process.
Considerable effort was also put into surface surveys to correctly tie in the positions of the relevant cave entrances, as this would have a great impact on the position of the caves relative to each other. In the search for a connection between the caves, accuracy of survey position will be a key factor for future expeditions, and a lot of work was carried out to ensure that the current understanding of the caves’ relationships is as accurate as it can be.

Cave of the Winds
A frustration for expeditions dating back to 1980/84 has been the difficulty in bridging the gap between Cave of the Winds and the Lagangs/Racer caves in the southern toe of the mountain. It appears that the Cave of the Winds streamway forms some kind of impasse to any further southwards extension of Clearwater, even though some 20 kilometres of cave passage lies only a few hundred metres to the south. Although the streamway had reportedly been ‘well looked at’ by previous expeditions, it was nevertheless decided to search it once again. Three small extensions were discovered, one which headed south into the blank area between Cave of the Winds and Racer Cave, and one which draughted well and entered a short section of substantial passage. However, none of the leads provided the hoped for link, and more work will need to be done in this difficult area to overcome what looks like a formidable geological fault separating Clearwater from the caves to the south.
Parties also scoured the walls in the large high level passages of Babel and Disillusion, looking for possible connections across the divide to the south. Once again, little was found in the way of promising or ongoing passage. The Cave of the Winds – Lagangs/Racer connection remains a conundrum.

Clearwater Cave
A clear objective of the expedition was to try and advance exploration in Clearwater Cave itself. Whilst being the best known and original cave of the Clearwater System, it had received very little direct attention since 1991, with successive expeditions visiting Hidden Valley, the Benarat caves, and then the recently discovered labyrinth of Whiterock Cave in northern Api.
A revisit was made to a passage discovered late in the 2012 expedition off Hyperspace Bypass. This produced 1.3 kilometres of new cave to add to the map, including a new entrance. It was noted that the passages had been previously used by nesters.
A key area for examination was the environs of Scumring and the huge shaft of Ronnie’s Delight. Investigation proved very worthwhile. Over eight kilometres of new cave passages were discovered, boosting the length of the Clearwater System to some 207 kilometres and elevating it to 8th longest cave in the world. But perhaps of greater significance was the fact that these discoveries were made at two new levels in the cave system, at heights where hitherto no cave was known. This is seen as a game changer; if these new levels of cave development also exist above the Whiterock/Blackrock areas of the cave system in northern Api, then the potential length of the Clearwater System is vastly increased.

A pitch head in the Creedence series | photo © Tony White

This will not necessarily be an easy undertaking, however. Exploration of the new high levels, named Creedence, required a determined assault by a very competent team who climbed up many shafts to access cave passage which is among some of the hardest going underfoot in Mulu. Long trips of several days with lightweight bivis were required to forge deep into the mountain, with a lack of water in the upper levels (partly due to very dry conditions) proving a major factor in the pace of exploration.
Nevertheless, most of the newly discovered passages were only left due to lack of time; open leads and strong draughts exist in many places, hinting at great possibilities ahead.
Due to the success of exploration in the Scumring area, other locations and leads originally identified for investigation remain unexamined. The potential in Clearwater is thus significant.


The sump at the upstream end of the Nasib Bagus streamway beyond Sarawak Chamber was identified as a good diving objective, and several days were spent with a large team assisting the porterage of compressed air bottles and diving equipment to a camp in Sarawak Chamber, and then up to the dive site itself. The dive turned out to be relatively short and shallow and led to 600 metres of clean washed canals and stream canyons, totally devoid of the usual swiftlet or bat life. The new passage ended in further small sumps and chokes under the edge of Hidden Valley, but there was very little in the way of side passages and the prospects for further extension here are small.
The water is assumed to derive from sinks at the start of Hidden Valley, rather than from the flood sinks or Damocles Cave area, whose streamway is believed to feed Cobra Cave but which remains to be followed. It had been hoped to put a team into Hidden Valley for this purpose, but the success of ventures in Clearwater and Easter Cave precluded a visit.
Several sumps in Lagangs Cave were also visited but were found either to be silted up or to have outlets which were too small to pursue.

Summary of surveys undertaken

Cave Surveyed length:
Lagang’s Cave 1554m
Easter Cave 4127m
Racer Cave (re-survey) 2850m
Cave of the Winds 397m
Nasib Bagus 603m
Total: 19139 metres (16289m new exploration)

NB these figures are provisional and will be confirmed in the expedition final report.


Members of the Mulu Caves 2014 expedition are very grateful for the support of the following
individuals and organisations:

From Sarawak:
The Chief Minister of Sarawak
The Sarawak State Secretary
The Director of Forests, Sarawak
Protected Areas & Biodiversity Conservation Unit, Sarawak Forestry Corporation
G.Mulu National Park Management & Staff
Local organisers and assistants
Oswald Braken Tisen
Rambli Ahmad

From UK:
Dick Willis
Commendium Ltd.
Makita (UK) Ltd.
Leica Geosystems Ltd.
Mark Wright Training Ltd.
Lyon Equipment Ltd.
Ghar Parau Foundation

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