March - 2019

Discovering Mulu’s longest river passage
by Hugh St.Lawrence

Tim gave me one of his weary looks – the one which is tinged with faint exasperation. I’d just announced that I wanted to go back into Whiterock to polish off some small leads, and with his imminent departure to chase bigger fish in Blackrock there was little he could do but silently fume at the Dark Lord’s waste of expedition resources on some little ramp that would probably just connect to the Northern Line. I think, like most people, he probably felt that Whiterock was pretty much worked out, or at least that ‘gains would not be commensurate with effort’. Fixing me with his ‘do you really have to’ stare, his mouth finally formed the words: “Well, if you can get a team together…”.

The team was soon assembled. Rambli, our Malaysian friend, had just joined the expedition and was keen to go caving. Gina had spent most of her trips doing scientific work and wanted some exploration. Adam, recuperating from a mystery illness, felt strong enough to accompany us. Loaded with the usual Mulu essentials like cake and cheese, we set off through the humid, humming forest. Three hours later we were at Propellor Camp, the central camp in Whiterock, and with Adam not feeling too good we cancelled plans to carry the camp forward to 1954, the big northern fossil passage – instead we would have to do our exploration from Propellor Camp, with several kilometres journey there and back. Adam felt better without a load and after lunch accompanied us up to 1954 via the delightful Lemon Squeezy and Upwind passages.

Our objective was a downward ramp on the western side of 1954. It was a leftover from our discovery of this big trunk passage in 2007, something I’d thought we ought to check out but had had no great hopes for. But a few days before, on a trip back from the end of 1954 with the Saga Holidays team, I’d stopped to check the ramp and descended an ever diminishing passage to a narrowing. It was too steep to continue on my own, but a noticeable inward draught was evident. The next day Matt, Richard and Dick surveyed the ramp a little further to another steepening which needed a rope. Back at camp we crunched the survey data, and the line plot suggested the passage was passing beneath the Northern Line…to where?

Gysum 'cotton' on the Ski Wednesday ramp | photo ©Hugh St.Lawrence

On the 8th March, Gina, Rambli and I set off down the bright white tube to find out. Leaving a still slightly crook Adam at the top, we picked up the survey, hung a rope on a short, loose scramble and continued down the inexorable 40º slope, powder dry and crystalline from wall to wall. In a side alcove we found the most amazing ‘cotton wool’ formation of gypsum needles and spent some time photographing this unique formation before continuing down the ramp. 120m vertically below 1954, ‘Ski Wednesday’ (the slope was so white and it was a Wednesday!) finally levelled out in passage appearing to run north on the strike. It did so as pleasant walking for 200m to a dead end, and an active side passage dropped down a 15m pitch to a choke. After surveying and photographs we returned to the bottom of Ski Wednesday for a chocolate break and then, ‘just for completeness’, surveyed into a flat out crawl going south. But we had hardly gone 5m into this before we knew we were on track again; we had the draught. It opened up only to lower into another sharp crawl, but finally the way rose into dry sandy tubes which progressed nicely for 100m before sloping down to a broad low junction. Passages went off in several directions, but from a steep ramp down to the right issued the sound of water.  It was too steep to get a proper look, but some wall of sediment appeared visible at the back, maybe a small pit with a shower? We didn’t at the time really think it could be more. There was only one way to find out and that was to come back with a rope and see. We trudged the weary kilometres back to Propellor Camp, contriving to get lost a mere 100m from camp! But tired as we were some of us didn’t get much sleep for thinking. What if?….

Ski Wednesday, the white ramp down from 1954 | photo ©Hugh St.Lawrence

Pleasant walking in Winterflora | photo ©Hugh St.Lawrence

The ramp with the sound of water | photo ©Hugh St.Lawrence

Gina, Hugh and Rambli at the bottom of Ski Wednesday | photo©Hugh St.Lawrence


After the great early discoveries in Clearwater Cave, the magnificent river passage had been followed northwards on subsequent expeditions to reoccur as fragments of streamway separated by sumps. Numerous sumps are bypassed by complicated and arduous routes deep into the far reaches of the cave to access Clearwater 5, then Clearwater 6 and 7, where the strong river rises from yet another sump. Northwards a fragment of the river is seen in Blackrock Cave as the Black Magic River with sumps at upper and lower ends. And that is very much that. Firecracker probably feeds the river via Black Silk sump, but this is a relatively small misfit stream. Where, the question has always been, does the bulk of the water come from?

During the 1980 expedition, Smart & Willis put dye in a sink (the ‘doline sink’) in the Melinau Gorge and this tested positive to the Clearwater resurgence 10.5 kilometres distant in 24 hours. The 1989 expedition repeated this experiment, introducing 2.5kg of flourescein into the doline sink. Again this tested positive to Clearwater resurgence, with positive samples also taken from the Clearwater 2 sump and the Black Magic river in Blackrock. Writing in Cave Science Volume 16 Number 2 (Aug ’89), Kirby concluded:

“From a study of the plan it seems probable that after entering the Silk Black sump the Firecracker streamway will swing to the south to reappear as the Black Magic River. Whether another streamway joins during this distance can only be speculation, however observations showed Black Magic to be in high flow conditions on a day when Firecracker was not, and vice versa, suggesting a tributary to exist which would take its feed from higher up the gorge.”

As a Mulu virgin in 2007 I visited the doline sink with Matt Kirby, and the thought that this small sink ran all the way to Clearwater was enticing if rather improbable. Indeed, we had visited the sink again on a surface survey just a few weeks ago, and John Palmer and I had wormed our way into a chaos of boulders with not a hint of passage in sight.  It wasn’t pleasant and was left for better things. But I suppose the thought was always at the back of my mind: the doline sink drains to Clearwater.


Whether from excitement or sleep we were revitalised the next morning, breakfasted quicky and set off with ropes and SRT gear. Adam had not been down the ramps with us yesterday so didn’t know the lie of the land, but I think Gina was excited at the prospect of something. I know I was. But I tried to put it out of my mind, it doesn’t do to premeditate cave! After a couple of sweaty hours commuting we were back at the broad junction. Leaving Gina and Adam to investigate the down ramp, Rambli and I set off to survey some tubes. An hour later we found a disconsolate duo waiting for us – Rambli had the extra rope in his bag! Once again we went off surveying and returned a second time an hour or so later. This time only Adam was waiting, and his grin told us all we needed to know. “Big river passage, going both ways”.

And what a spectacular way to enter it! The 40º tube angled down a rope’s length and then just burst into the roof of a 40m diameter passage. In my excitement I bungled the knot pass but it didn’t matter – the free-hanging 20m pitch was an awesome entry into what we had hardly dared believe could exist – the Whiterock River. The pitch landed on an expanse of boulders 20m above the river. North or south, we had to choose? We went north, traversing a large slope of boulders to reach the river where there was more boulder hopping for several hundred metres in roomy passage of the 20m to 30m variety. Eventually the boulders gave way to easy walking on sediment banks in an arched tunnel 20m wide, the crystal clear river flowing in a trench to the side. 700m from base Gina and I left the survey near a prominent inlet. Downstream we didn’t even touch.

One of the quick 'snaps' to prove what we'd found! | photo ©Hugh St.Lawrence

Spectacular entry to the river passage | photo ©Robbie Shone

Adam, Gina and Hugh after first exploration of the river | photo ©Hugh St.Lawrence

Survey graphic of the river area | ©Hugh St.Lawrence


All the while we had to keep pinching ourselves – was this for real? Our excitement was palpable but suffused in a strange,  awestruck silence, broken only by Gina shouting out the survey numbers. We’d look at each other in bemused amazement, hardly daring to say anything in case we broke the spell of this magical moment – there’s something so special about finding river cave deep in a mountain, and we were being treated to a very special section of river cave indeed. It was so evidently big and ‘going’ that we worried that no one would believe us if we told them. “Oh yes, miles of river cave, yeah yeah yeah, pull the other one it’s got bells on”…we could already feel the piss being taken! So we spent another hour taking some photos with our one and only small camera – it was at least some evidence! The next day we bounced out of the cave and Gina more or less ran all the way back to Camp 5 to announce the news, grinning like the proverbial Cheshire!

The find set the expedition buzzing and a frenzy of activity in the final days saw the river pursued south for 1.7 kilometres, mostly pleasant walking with the occasional wade, with a major sumped inlet from the east after 400m, and left wide open. Northwards from the inlet where we’d left the survey a further 1.1 kilometres of easy paddling were surveyed to a junction which turned out to be close to but 60+m below the Camp 5 area. Active inlets entered but were not pursued, a northerly passage was only briefly looked at, and a dry southerly passage was investigated down the strike for 400m without end. A further kilometre was surveyed in the prominent inlet and many open leads were observed. And perhaps of most significance, bats were seen flying in and out of a small passage near the top end of the river.

The Whiterock River was a fabulous discovery. There’s something special about river passage, the feeling of active cave, nature at work, the beauty and burbling of the crystal clear water. It was certainly a privilege to find it. And this was fairly special river passage, 3.5 kilometres of virtually uninterrupted walking from end to end, the longest open river cave section in Mulu. And still it hasn’t ended!

The Whiterock River in relation to Whiterock and Blackrock caves


Of course, the river discovery would never have happened without all the hard work put in by other teams who have pushed and paved the way into the mountain since the cave’s chance discovery in 2003. It also validates the theory by Kirby and others that a tributary stream from the Melinau Gorge joins the waters beyond the Silk Black sump before appearing in the Black Magic and thence Clearwater rivers.

But what next? Downstream is wide open but the survey data suggests an altitude very similar to the Black Magic upstream sump 2 kilometres south. If the data is right, one might expect a sump fairly soon, or long sections of wading or swimming in low gradient passage. There’s potential indeed, but it might be tempered by datum levels. The major inlet at the 400m downstream mark brings in maybe 30% of the total flow. This passage terminates in a sump, but looking for a bypass might be well worthwhile. Several other ramps up from the downstream river may lead to new passages or to connections into existing cave closer to the Whiterock entrance, which would cut out the long trek to the entry via 1954.

Upstream, the river has several tantalising possibilities. Inlets such as Swiftwater and Animal Track are not fully explored and open leads await in them. But near the top end of the river things get really interesting. Here the river passage cuts east across the beds to Pointless Junction. Just before here bats were observed flying in and out of a small passage on the north bank. This was investigated for 30m and was mostly crawling and inconclusive, but bats would seem to suggest the proximity of an entrance. At Pointless Junction itself a small 1m high passage brings in a good flow of water and was not followed. Also at the junction a larger broken passage heads north but only one survey leg was put into it to establish direction. To the east the passage enters a tall chokey area with large boulders, slippery calcite and an inlet waterfall. A passage behind the waterspout was not fully followed.

South from the junction rises to a platform and then descends gently into a shallow lake passage with 20cms of water on a cracked mud floor. Shortly beyond, a shingle bay appears to terminate the passage below massive boulders covered in slippery moonmilk. These repelled initial attempts at climbing but a big echo was noticeable at this point; whether this is the acoustics of the lake passage or something larger above is not known. Below the boulders a low stooping passage for 30m emerges in good going again and the cave continues in easy style southwards down the strike for at least 300m without end. This passage must be in one of the most easterly and oldest beds in the Clearwater system, who knows what it will bring.

The doline sink lies approximately 400m east of Pointless Junction and 75m above it. It is assumed that one of the active inlets here is from the doline sink and a dye test would probably quickly establish if this is so and which one it is. The other inlets are presumably from unknown sinks or river leakage through the alluvial gravels.

The real tantalus, of course, is whether any passage can be followed north from the junction under the gorge towards or even right on into Benarat itself. The northern terminus of the Whiterock River is at least 60m vertically below Camp 5, so probably well into the limestone and below the alluvial river gravels. A broken passage does appear to head north and has not been explored. This whole area is worth a thorough search, either for a northern entrance or for a sub-gorge connection with Benarat. The latter would be of momentous importance!

The River upstream of the entry point | photo ©Robbie Shone