The Underground World of Mulu

by Kevin Dixon through rattan and vines; climbing through roots, dense undergrowth, and limestone pinnacles; wad- When the Internet seems to have all the answers ing through streams and mud; and frequent tropical and the earth is revealed in ever more detail, it storms. Most people stay fully covered, despite the is refreshing to find a part of the planet that is heat and humidity, so as to avoid cuts and scratches still being discovered, even after thirty years that can quickly become infected. It also provides of exploratory expeditions. In Mulu, , some protection against the leeches, horseflies, and , what was created over millennia by mosquitoes. water pushing through the limestone bedding and faults to find the quickest route to the sea The success of early expeditions conducted by the is now a crystal underground world inhabited “Mulu Project” depended to a large extent by bats and swifts. Surveying has been essen- upon good surveying. The surveys were needed not tial to the continuing discovery, providing maps only to illustrate the amazing discoveries being made to guide the explorers back to their starting but also because much of the scientific program point; showing potential new entrances as they relied upon accurate surveying. Nearly all the approach the surface; and hinting at new discov- passages were surveyed as they were discovered by eries as cave passages follow major faults, bed- small teams of two or three surveyors. The instru- ding planes, and drainage horizons. But what sur- ments typically used were compasses and clinom- veying technology and methods have survived eters with 30 m (100 ft) fibron tapes. Back at camp, this harsh environment to map this 3D maze? survey drawing was limited to transferring notes onto graph paper with the help of a protractor and Conditions within Mulu are not ideal for surveying ruler. Later, programmable calculators made the task equipment, or people for that matter. The humidity much easier. Field drawings were always limited to is typically 100 % and the temperature 30 °C (86 °F). graph paper and were drawn up in ink and Letraset Getting to the caves still requires machete work only after returning to the UK. >>

The Global Magazine of Leica Geosystems | 15 Surveying Today – with Leica DISTO™ targets. By surveying extra long legs, we expected Laser Distance Meters the accuracy to be improved compared to more tra- The 2011 expedition had a number of ambitious ditional, shorter survey legs. goals over the scheduled six weeks, many of which were surveying related. Teams of 2 – 4 people did It was the first time we used the Leica DISTO™ DXT. the surveying with one designated note-taker field Its higher IP rating (IP65) meant greater resistance to sketching the cave and tabulating the readings on a mud and water. This was an advantage as we could waterproof notepad. A second person operated the keep the DISTO™ DXT slung around our necks, ready instruments, shouting the readings to the note-taker. to use for quick measurements of passage dimen- sions – usually left and right walls, ceilings and floors Leica DISTO™ DXT and DISTO™ D8 laser distance in the direction of surveying. We used the same meters from Leica Geosystems were taken on the equipment and techniques for surface traversing Mulu 2011 expedition in addition to compasses and to connect cave entrances to fixed control stations. clinometers. The DISTO™ D8 with a built-in clinom- A feature of both laser distance meters that was eter meant we could reduce the number of clinom- greatly appreciated was the internal memory, which eters used plus it had the advantage of greater allowed the note-taker to check results and avoid inclination accuracy and could measure up to 200 m transcription errors. (656 ft). We had to avoid water and mud with the Leica DISTO™ D8 but it was worth it as we measured Establishing Controls distances of up to 186 m (610 ft) to reflective targets, A dual frequency GPS receiver, a Leica SR530, was often using the Leica DISTO™ D8 digital pointfinder taken on the expedition to determine a set of consis- with our high-powered headlamps to identify distant tent control points across the Mulu area, with partic- ular emphasis on accurate height determination. Sta- tions were determined by the availability of a clear sky for good satellite visibility, which in primary jungle is difficult to find. Some stations were set in clear- ings that had been made within the park by the local authorities for emergency evacuation by helicopter. One location, just outside the park boundaries, had been recently cleared by the indigenous population. Thankfully, satellite visibility was good and the sur- vey did not have to be repeated. The static 30 sec- ond GPS data was Precise Point Positioned (PPP) by the Jet Propulsion Laboratory, using their free online service. The resulting absolute position accuracies ranged from 0.02 to 1.09 m (0.8 to 42.9 in), with the majority at the 0.1 m (4 in) level or better. The 1.09 m (42.9 in) result was not unexpected. It was from the worst site for visibility at the Terikan River Resur- gence with a narrow field of view above the river and a large cliff immediately to the east.

Expedition Summary A total of 15.2 km (9.4 mi) of new cave passages were explored and surveyed, which included adding 13.4 km (8.3 mi) to the Clearwater System, making it 189 km (117.4 mi) long and the 8th longest cave in the world. Two new caves were found and surveyed. Eight geodetic GPS points were surveyed. A total of 26.2 million laser scan data points were collected Robbie Shone drawing up the Mulu Caves. from Deer Cave and Sarawak Chamber, traversing

16 | Reporter 66 3.4 km (2.1 mi) with 36 setups. Sarawak Chamber, crystal speleothems, the formation of which is not the world’s largest underground chamber, was pho- yet understood. Large areas of Mulu limestone have tographed using Megaflash bulbs and a Panorama no known cave. This is sure to spur future expedi- setup. tions.

What takes people half way round the world to suf- About the author: fer, survey, and pay for the privilege? Curiosity and Kevin Dixon is a Fellow of the Royal Geographical wonder seem to play a large part, knowing that you Society, a Land Surveyor with a Degree in Computer are the first person to explore and survey a place, Science and Mathematics from the University of York, finding out what is round the corner and discovering UK, where he is based. ([email protected])

The Mulu Caves Project and Gunung Mulu National Park

The Mulu Caves Project is a collaboration between guides are also available, starting from the recently UK and Malaysian speleologists and the Sarawak renovated park headquarters. Camp 5 is in a beauti- Authorities in Malaysia. The expeditions are largely ful setting and is used as a base camp for viewing the self-funded by the members and usually take place razor sharp blades of the Limestone Pinnacles, some biannually. Preparations are lengthy and involve con- reaching higher than the rainforest canopy nestling siderable assistance from the Sarawak Authorities, between them. Much of the wildlife is nocturnal, a Sarawak Forestry Corporation officials, and National slow walk along a jungle trail at night is often well Park management. rewarded. Mulu has its own airport with regular flights from and Kuching. (www.mulupark.com) Gunung Mulu National Park is well worth a visit, espe- cially taking a walk through Deer Cave before watch- A good collection of photographs for the Mulu region ing the evening exodus of the estimated 3 million including caves and wildlife can be viewed at bats. Several adventure cave trips with experienced www.shonephotography.com.

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