March - 2019

Mulu Caves 2018 Expedition was the 26th Anglo-Sarawak Expedition to Gunung Mulu National Park and operated in the field between 12th and 29th of January 2018.  The expedition was to investigate airflow within the caves, search for cave entrances in the Melinau Gorge using a camera drone and commence a re-survey of parts of Clearwater Cave where early data had been lost. The expedition was based for the first week at Park headquarters then moved up to Camp 5 for the final week.  The team was led by Hugh St.Lawrence and included a total of six members from the UK, one from the USA together with one from our hosts at Sarawak Forestry.  The expedition was further assisted by National Park Management, staff and local people.

Wind Logging
Wind (or draught) logging had not been carried out in Mulu before this expedition so these trials were the early stages of what could become a long term project. here has been a great deal of anecdotal evidence about draughts but little hard evidence regarding direction or strength or when the draughts are at their maximum. Considering that draughts have been heavily relied on for finding new cave entrances this study is long overdue. Indeed it can not be certain that entrances have been missed simply because the draught was at its minimum at the time the explorers passed by.

Windsonic anemometer on tripod

The expedition brought two ‘Gill Instruments’ anemometers to the Park together with pressure/temperature/humidity loggers. Loggers wereplaced in positions where strong draughts are known to exist. These include:
• In Cave of the Winds they were installed in Overtime and Illusion passages. It had been hoped to install a logger in the wet/lower entrance to Cave of the Winds, however, owing to heavy rainfall and high river levels there was concern over the safety of a logger in this position.
• In Clearwater Cave they were installed close to the Scumring bivouac site in the Snow Slopes and Ronnies Delight passages.
• In Whiterock Cave a single logger was installed at the Midnight Entrance and left to run for three days.
• In No Country for Old Men a single logger was installed at the entrance to the first squeeze and left to run for three days.
Wind logger in position at the Snow Slopes site in Clearwater Cave 15-16 Jan 2018
Graph showing wind speed and reversal at the Snow Slopes site
Initial results confirmed that there are reversals of air movement within the caves. This was clearly demonstrated at the Snow Slopes which normally supports a huge draught in a relatively large passage. Peak air flows of 2.5m/s (peaking to 3m/s) were experienced with a reversal of -0.75m/s (peaking at -1m/s).
When installing the logger in the Midnight entrance to Whiterock Cave it was noted that the airflow at the logger site was inwards whereas 400m further into the cave the airflow was outwards. The logger revealed that reversals of flow occurred with an inflow during the day time and outflow during the night. Further work with multiple loggers is required here to better understand the air flow dynamics in this part of the cave.
In addition to the wind loggers, pressure loggers were also used to determine the atmospheric pressure, temperature and relative humidity at the test sites. These revealed a fairly constant temperature of 23.7 ºC and a relative humidity of 100%.
In conclusion, the results indicate that the draughts do indeed vary with time and can reverse in certain circumstances and that they are at their strongest around 17.00. In general further work is required to determine what drives the draughts and in particular whether there is an optimum time to search for new entrances which require an outward flow of air to be located.

Camera Drone Work

Above the clouds in the Melinau Gorge

A DJI Mavic Pro camera drone was used to search for new entrances on the Api side of the Melinau Gorge in areas which are difficult to access due to the nature of the terrain. It was hoped that new drone technology would allow a view of potential sites without the need for ‘feet on the ground’.
One existing ‘entrance’ which has eluded explorers for many years is known as Canopy Cave. Many expeditions have tried unsuccessfully to gain access to this prominent feature and there has always been some doubt whether it is in fact a cave entrance or simply an alcove of rock. The drone was flown from the heli pad at Camp 5. This gives a good line of sight along the gorge, however, Canopy Cave entrance is not visible from the launch pad so the risk of loss of communication with the drone was considered a high possibility. A ‘return to home’ from that location could result in a collision with high ground on the return route. Therefore close inspection of the entrance was not possible.

Drone shot looking into Canopy Cave

• Cliffs to the west of Canopy Cave
A line of cliffs lies to the west of Canopy Cave between it and the Pinnacles track ridge. This is in ground which would be very difficult to access on foot. Once again the risk of loss of signal was considered high so close inspection was not possible although a clear view was obtained from the Benarat side of the gorge.
• Cliffs to the rear of Camp 5
The northerly trending passages of Whiterock Cave all end in calcite blockages extremely close to the cliffs behind Camp 5. Unlike the Benarat cliffs, where entrances are obvious against the white limestone face, on the Api side of the gorge the slopes are heavily vegetated and it has been impossible to find any entrances which may connect into the Whiterock system. Some photographs taken during helicopter fly-bys have hinted at entrances behind the trees but it has been uncertain whether these are indeed cave entrances or just shadows. The use of a camera drone to gain close up images has been seen as essential to determine whether the dark shadows are cave entrances which require further investigation by climbing. Unfortunately close up photography did not reveal any new entrances.
• Benarat Cliffs
Two possible entrance sites had been seen using binoculars from Camp 5. The drone confirmed that these do appear to be cave entrances, although 400m above ground level.
• Canopy Cave

Clearwater Re-survey

Fixed station marker

All the original survey data from the ’78 and ’80 expeditions for Clearwater Cave, Cave of the Winds and Benarat Caverns have been lost. At that time the data was used solely to draw the surveys and once completed there was no further use for it. However, times have moved on and we are now in the ‘digital’ age. Modern surveying methods input field data to computer based programmes to produce centre line surveys onto which passage detail is added. During 2005 all available data was input to the ‘Survex’ programme to produce a master dataset. Unfortunately this did not include Clearwater, Cave of the Winds or Benarat Caverns, three of the most important caves in park.
Fortunately a solution was at hand, to re-work the original paper plans and elevations to produce Cartesian x, y and z coordinates which could be input to the Survex model. The downside of this process was that it produced a single cave file (named Clearwater Fake or Benarat Fake) for the whole of the three great caves which was in a different format to that of all the other data. Although a Cartesian file works well in Survex it is extremely difficult to connect new passages into it as there are no fixed stations or marker cairns in the cave.

The only long term solution to this was to resurvey all the ’78 & ’80 passages.

Installing the tag at Clearwater entrance

The method would be to run centreline survey lines through the main passages and install fixed survey markers at key junctions which could be used at a later date to continue the work. This expedition ran a survey line through Cave of the Winds to the Hyperspace Bypass area of Clearwater and installed fixed stations at

• Cave of the Winds upper entrance
• Seven Pillars of Wisdom Junction
• Bable Junction
• Start of Wan Way Street (Clearwater connection)
• Base of Hyperspace Bypass
• Clearwater Cave main entrance
• Clearwater Cave main passage below the Balcony Series
An attempt was made to run a survey line up the Clearwater river, but owing to high water conditions this was abandoned at the second rope crossing and a survey marker installed at the junction with the Balcony Series. This can be easily picked up at a later date.

As with all Mulu expeditions exploration was high on the agenda but this took second place to the principal aims. With the loggers in place and running there was opportunity to have a look for new leads.
• Moonmilk Cave
Moonmilk Cave is the small cave through which the Clearwater plank walk passes. A previous walk through this cave suggested there was more to the cave than the original survey indicated. A small team explored approximately 180m of new passages which revealed two new entrances overlooking the Melinau River
• Cave of the Winds
During a resurvey in the entrance series of Cave of the Winds a side passage was surveyed to the previous end point but a draughting tube was seen heading upwards. This was followed for approximately 70m to a short rope pitch and a series of small interconnected rifts below. These were not pushed to a conclusion but this area appears to be under the floor of Not Before Time Passage.
• Quatermass Series
This passage lies approximately 100m east of the Scumring bivouac site just off the Snow Slopes. Initial exploration was carried out during the 2017 Easter expedition ending in two vertical drops.

Mark Jones with mighty stalagmites in the Road to Hell

This expedition explored the pitches to conclusion with 168m of passage explored.

• Armistice and Red Dwarf Chamber
Whilst the Scumring loggers were running a party visited Red Dwarf Chamber at the far end of Armistice North Passage. This large boulder-filled chamber, at the very north of Clearwater Cave, had only ever been entered by two people in 1989. At the time of original exploration no draughts had been detected and no obvious leads left unexplored, however, there was always a question whether a second look may reveal a way on or a draught which had been missed. Unfortunately the re-visit did not reveal any new leads. This is a very beautiful part of the cave with many splendid formations, now only ever seen by five people.
It is unlikely that this part of the cave will be visited again in the near future, if ever.

Expedition Members

The 2018 Team

Related Articles

2018 Preliminary Report

Diary of a New Recruit, by Mark Jones