Tales from the Underground... by Andy Farrant

Looking up into the roof of Deer Cave,
home to 3 million bats
Deep beneath the jungles of Borneo are some of the worlds most spectacular cave systems and right now our intrepid geologist and caver Dr Andrew Farrant is exploring and surveying deeper than ever before...
It is dark when I wake up. Pitch dark. Above I can hear hundreds of swiftlets chattering in the dark, finding their way through this, one of the biggest cave systems in the world. Turning my light on, tell-tale glints of light down the passage mark the location of Huntsman spiders lying in wait for an unsuspecting cave-cricket, their eyes reflecting my light. Rising above is the huge void of Hyperspace, a massive chamber over 100 m across lying hidden beneath the tropical rainforests of the Gunung Mulu National Park in Sarawak. Today, we are heading out to daylight after a 3 day camp in Clearwater Cave. At around 200 km long, it is one of the top ten longest caves in the World.

Returning to daylight. At the entrance after 3 days
underground. L-R: Carl Clark, Tony Radmell, Professor
Peter Smart, Dr Andy Farrant (photo Fran White)

It has been 23 years since I last trod this spot, when I was a young postgraduate student at the University of Bristol, and today my former PhD supervisor (Professor Peter Smart) is in our team. Yesterday we had pushed a passage which led into 1.6 km of new cave, eventually emerging at a fine entrance high above the Melinau Paku valley, surveying as we went. Ancient gravels, long abandoned by the formative stream and now perched 300 m above the Clearwater River littered the passage floor, sometimes capped by stalagmites. The gravel composition, imbrication and cross bedding combined with dissolutional flow markings on the passage walls yield clues to the direction of water flow and the discharge of this ancient river. It is these stalagmites and sediments that provide the key to the age of these caves.

Weathered remnants of volcanic ash deposits; here
they once filled this passage, but have been subsequently
washed out, leaving remnants on the cave roof
Stalagmites can be dated by Uranium series dating and hence give a minimum age for the passage. Relict sediments in high level passages such as the one we had just found preserve evidence of palaeomagnetic reversals, the last occurring around 780,000 years ago. The data suggests that the highest caves are probably 2-3 million years old. Combining the Uranium series and palaeomagnetic chronology with observations of sediment and cave geomorphology enables a record of landscape evolution to be constructed in an area where all the surface evidence has long been destroyed. Elsewhere in Clearwater Cave, deposits of waxy white clay are remnants of volcanic ash deposits washed down into the cave (photo right). These bear witness to massive volcanic eruptions that periodically blanketed this part of Borneo with thick deposits of ash over the past few million years.

Looking out of the Secret Garden entrance to Deer Cave;
the immense size of the passage (nowhere less than 100m
high) can be gleaned by the rainforest trees in the entrance
This time, the research is focussed on investigating the swiftlet and bat guano upon which the rich cave ecosystem depends ['bottom' photo for those with strong stomachs- ed]. Faecal sterols within these deposits have the potential to act as geochemical markers, whilst the acidity generated by guano decay alters the limestone and contributes to cave enlargement. A key site for this study is Deer Cave. Over 3 million bats live in the roof of this huge void, which at over 100 m high and wide is the biggest passage in the World. Yet the guano piles are less than a metre deep, highlighting a rapid recycling rate by the myriad of insects that live in this twilight zone.

Back at the base camp at the National Park HQ, other members of the expedition return with tales of yet more kilometres of huge passage discovered; all providing additional clues about the tectonic, climatic and landscape evolution of this part of Southeast Asia.

Thanks to Andy Eavis and members of the Mulu Caves 2014 expedition, to the Gunung Mulu National Park and the Sarawak Forest Department.

More details can be found at http://www.mulucaves.org/
Andy Farrant

The guano from 3 million bats hosts a diverse ecosystem within Deer Cave, including cockroaches, spiders, centipedes, crabs and cave crickets