Caving Expedition on Borneo

Entrance of The Cathedral and Gua Tung Hap



Caves of Tabin Wildlife Reserve

Louise Korsgaard1 and Torben B. Redder2
1Institute of Geography
Copenhagen University
Oestervoldgade 10
DK-1350 Copenhagen
Denmark

2Vognborgvej 5, 1.
DK-2400 Copenhagen NV
Denmark

Abstract

The biggest limestone outcrop in Tabin Wildlife Reserve was explored with the aim of finding caves. The search resulted in the finding of 36 cave entrances and the mapping of 23 caves, most of which were located near the northern summit. All these caves most likely formed part of an ancient cave system. A total of 1200 meters of this system was explored during the expedition and it included caves as well as canyons and dolines. Due to unstable boulders, not all of the caves were entered and surveyed. The biggest chambers found were Gua Tung Hap (width x length x height=15m x 30m x 30m), The Cathedral (10m x 25m x 10m) and The Shaft (20m x 20m x 30m).

The ancient cave system was probably formed by an underground river prior to the uplifting of the limestone hill relative to the surrounding area. The present topography cannot explain the formation of such cave systems.

The old cave system is now fractionated by numerous collapses, most of which have taken place more than 300 years ago. However, some recent collapses, less than a year old, were seen. They reflect the still ongoing weathering of the limestone and disintegration of the cave system.

A unique flora and fauna was found in the caves and sinkholes (collapses). Furthermore, the area might contain archeologically and paleoclimatic interesting sites. All this, along with several other factors, serves to justify the preservation of the area. If development of the area is to take place, eco- and adventure tourism will be highly suitable, given that all the necessary precautions are taken.

Introduction

Sabah has numerous small limestone outcrops containing caves. The most thorough description of these caves is found in the book `The Geology of Sarawak and Sabah Caves´ by G. E. Wilford (Wilford, 1964). Four limestone outcrops are believed to exist in Tabin (Ping and Kiew, 1997), but no caves have been described and scientifically investigated. However, the local people knew of some caves in Tabin, which had been visited by Ibans and Chinese in their search for the valuable birds nests. According to Haile and Wong (Haile and Wong, 1965), the Tabin limestone is of late miocene age, and thus old enough to have developed caves. It therefore seemed natural to include a cave research team in the Tabin Scientific Expedition II. Because of the limited time for research and the numerous caves found, research was concentrated on the biggest limestone outcrop. 

 The formation of caves.

Limestone consists mainly of calcite, CaCO3, which is highly soluble. Limestone caves are formed by the dissolution and removal of calcite by acidic water. Rainwater contains small amounts of carbonic acid and is capable of dissolving limestone. However, as rainwater infiltrates soils, the presence of organic acids and the high CO2 concentrations of soil air, greatly increases the acidity and thus the dissolution potential of the infiltrating water. (Gillieson, 1996).

Caves can be formed below the water table by the movement of groundwater (phreatic caves) as well as above the water table by the action of underground rivers and streams (vadose caves). The shapes of the cave passages as well as the structure of the cave systems is largely determent by the nature of the bedding planes, faults and joints present in the limestone. Furthermore the lithology (primary porosity, hardness, crystallization, purity) of the limestone controls the types of caves being formed. (Gillieson, 1996).

As the water table is lowered due to uplift of the limestone or to fall in sea level, many caves become dry and are termed fossil caves. In these caves extensive deposition of calcite in the form of stalactites, stalagmites and flowstone takes place. These calcite depositions can completely fill up a cave passage. Due to surface weathering of the limestone, the caves will get closer and closer to the surface. The roof of the caves will eventually be exposed to surface weathering resulting in a loss of strength and finally a break down of the caves. This creates more or less circular, steep sided holes called collapse sinkholes or collapse dolines (Ford and Williams, 1991).

Methods

The goal of our participation in the Tabin Scientific Expedition II was to find, map and survey the caves. Our team worked from October 15th to October 26th.

The cave entrances were located by visually searching the limestone and by the knowledge of the 3 locals participating in our team.

The cave entrances found were mapped by the use of a GPS. In most cases the reception was good, but in some cases the reception was very poor and it was not possible to get an exact position for the cave. 

Caves of Sabah and Sarawak are mostly horizontal and therefore normally do not require specialized caving techniques using rope. However surveying the caves found in Tabin sometimes required the use of rope, harnesses and other specialized caving equipment in order to enter shafts of up to 30 meters deep. Some places the ropes could be secured to trees, but other places it was necessary to put expansion bolts (Petzl, 8mm). The survey of the caves was done with compass, clinometer and measuring tape. The surveys are of grade 1 (Ellis, 1995).

Some of the caves were given names. This was done only to ease communication and navigation. The names are by no means official.

Results 

During the expedition 36 entrances were found, leading to a total of 23 caves. Most of these were found in big collapse sinkholes located near the northern summit of the limestone hill and they had very steep or vertical access. These are referred to as system 1, 2 and 3 in the following. One cave was found near Sungai Burung at the foot of the southwestern end of the hill and another was found in the limestone cliff, 10 meters above the main trail from the base camp to the hilltop. A lot of big cavities were encountered in the boulders at the western base of the hill. These are not caves, but merely spaces between big blocks of dislodged limestone, and will not be included in this report.

Location

Positions of caves (GPS, WGS 84)

N 5º **,***'

E 118º **,***'

Bat Cave

18,718

44,931

Big Sink

18,761

44,968

Camp

18,862

44,701

Gua Bau

18,722

44,952

Gua Harapan

18,585

44,764

Gua Tung Hap

18,806

45,028

Gua Tung Hap (shaft)

18,813

45,023

Gua Tung Hap (shaft)

18,816

45,016

Lunch Doline

18,747

44,963

Northern Shaft (1)

18,887

45,112

Northern Shaft (2)

18,891

45,115

Silo

18,762

44,926

Small entrance

18,658

44,798

Small entrance

18,666

44,814

The Cathedral

18,774

44,987

The Cathedral (10m shaft)

18,785

45,007

The Shaft

18,766

44,990

Tree Doline

18,673

44,859

View Point

18,768

44,923

Gua Sg. Burung*

17,860

44,046

Kuala Sg Burung / Sg Tabin (reference point)*

17,885

43,934

Stream*

18,540

44,802

* not shown in the map

Caves in the northern part of the limestone hill

System 1:

The biggest cave chamber and the northern most cave explored is Gua Tung Hap with its 15m x 30m sized floor and 30 m height. This cave is connected to thesouth to a 120m long, 4m wide and 20m deep canyon, which prior to break down must have formed part of a big cave system. Both ends of this canyon are blocked by boulders, as is the case with nearly all of the caves found. Another big canyon, that used to be a cave, connects the northern end of Gua Tung Hap to The Cathedral, which is a picturesque 25m long tube formed passage of 10m width x 10m height. As in Gua Tung Hap, some stalagmites, stalactites and flowstone have been formed in The Cathedral, none of them, however, of any impressive size. In the canyons very big stalactites were seen, often decorated with one-leaved plants and ferns. The southwestern end of The Cathedral gives way to a beautiful circular green garden. In the southern end of this garden, a shaft connects to The Shaft, a chamber 30m high, 20m wide and 20m long. The Shaft is connected to a long passage (60m) running southwest, but unfortunately also blocked by boulders and flowstone. A weakness in the surface above this passage leads to Lunch Doline, and a connection is thus very likely. In Lunch Doline, which is easy entered through a nice arch cave, four small caves were explored but none of them continued for more than 10 meters. One of the caves, however, proved to be connected to Big Sink, an impressive 25m x 25m and 30 m deep hole northwest of Lunch Doline. In Big Sink two chambers were explored and a connection to the garden southwest of The Cathedral was confirmed. A shaft below this connection was not explored due to the unstable nature of the surrounding boulders, but it did look quite promising.

This system thus consisted of at least 500 meters of connected passages and chambers

System 2:

Another system, including Gua Bau, Bat Cave, Gua Babi and all the shafts towards Tree Doline and Tree Doline itself, had a length of 250 meters. Most of the caves in this system were also separated by collapses, but the caves were smaller and spaced closer together than the caves in the previously described system. Most of the caves were inhabited by thousands of bats.

System 3:

An up to 7 meters deep and 6 meters wide canyon was followed for 450 meters. It started near Bau Cave and ended in the cliff face. A few caves were explored in the canyon of which the biggest was Gua Harapan, 5m wide 10 m long and 6 m high. A small passage continued another 10 meters. No collapse had occurred in this end of the cave, but the passage was totally blocked by flowstone. A few shafts in the canyon were not entered as the collapses that had revealed the caves were very new and thus unstable. Furthermore, due to the extensive collapses, that once formed the canyon, a big cave was very unlikely to be found in the canyon. 

Although not proven, it is highly possible, that these three described systems are connected, and that the Northern Shafts, The Silo, The Amphitheater (near View Point) and several observed canyons forms parts of the systems as well. The entire system would then consist of 1200 meters of connected passages and chambers.

Other caves:

First Cave located near the main trail, was a small 2mx2m tube that could be followed for 20 meters before it was filled in with sediments. The limestone in which the cave was found was very soft and unconsolidated.

The southern part of the limestone hill

Gua Sg. Burung was the only cave found in the southern end of the hill. The cave was 20m long, 5 meters wide and 4 meters high and located approximately 2 meters above Sg. Burung. The floor was covered with fine fluvial sediments, and it is likely, that Sg. Burung enters the cave during floods.

Cave biology

Many of the caves were inhabited by thousands of bats (see article in this monograph). The bats sometimes made the exploration very uncomfortable. Large amounts of guano supports whole ecosystems in the caves and make them very smelly. No swiftlets were seen in the caves. This corresponds well with the earlier findings by eager birds nest hunters. Many snakes were spotted in the cave entrances and their sloughs were a common sight. Most of the snakes were harmless cave racers, which are extremely good climbers and feed mainly on bats. Footprints of wild boars and deer were seen in some entrances. In Gua Babi the mud floor was entirely covered with footprints.

Discussion

The entrances and caves near the northern summit of the limestone hill seems to be the remains of an impressive cave systems running more or less parallel to the ridge and maybe representing the major fault lines. This big system has been disintegrated by numerous collapses leaving only fractions to be explored by this expedition. 

Most of the collapses have occurred more than 300 years ago judging from the big trees growing in the sinkholes. Some of the collapses, however, appeared to have taken place less than a year ago, and many of the boulder slopes were extremely unstable. Furthermore the roofs of many caves were thin and dissected by fractures. This indicates, that the area is still undergoing large geomorphological changes due to the weathering processes. Soil is virtually non-existing in the cave areas and the ground vegetation is sparse. Only a few trees have survived the unstable, dry and nutrient poor conditions. Some lush gardens, for example the one immediately southwest of The Cathedral, were found in sinkholes covered by a thin layer of soil. These sinkholes are probably the eldest in the area. A few rare (new?) species was found among the plants collected in the sinkholes.(see elsewhere in this monograph).

Only a few and mainly small stalagmites, stalactites and flowstone were seen. The reason for this limited deposition of calcite in the caves may be due to the fact that the percolating water only contains very little dissolved calcite as the roofs are very thin (limited source of calcite) and the acid generating soil layer is more or less absent (low dissolving potential of water).

The canyon like shapes of the caves indicate, that they were formed under vadose conditions, that is after the limestone was lifted above the watertable. As the roofs of the caves are very weathered or collapsed it is not possible to state whether the caves were initiated under phreatic conditions prior to uplift or are purely vadose. An exception to this is First Cave. Its tube-like shape is very typical of a cave formed under phreatic conditions.

The present topography cannot explain the formation of the caves, as the amount of water needed for the formation of such big caves cannot be gathered from the limestone itself (autogenic drainage). A much larger catchment area is needed. Limestone is much more resistant to weathering than the surrounding mud and sand stone, which explains the current topography. But a long time ago, the limestone was located in the lower parts of the relief, thus receiving water from a greater area, maybe even including the catchment area of Sg. Tabin. As the limestone was uplifted, the underground rivers carved deep canyons and cylindrical pools. At one stage, rates of uplift have forced the river to find new ways and old passages were left fossil. These new ways could be in the limestone below the explored systems, or the river could have entirely abandoned the limestone due to its increasing height above the surrounding area. The big boulders found at the foot of the hill, could indicate major undercutting of the limestone by the river.

Potential for further findings

Caves

Due to the limited width of the limestone hill and the apparent absence of entrances along the foot of the hill, the potential for finding more caves is limited. However, the existence of a cave system running parallel to but below the explored system is possible and the potentials for further findings lies in the exploration of the unstable vertical shafts to the north and south of the main cave area, as well the shaft below the connection between Big Sink and The Cathedral. Furthermore, a thorough investigation of the cliff in a southwestern direction from the main trail could reveal some entrances. This will require climbing techniques.

 The big amounts of debris covering the western foot of the hill may hide many entrances to a lower system. Some indications of this were found in a small entrance, which had a cave-like appearance, but was totally blocked by boulders and flowstone. Finding these will require lots of digging and good luck.

 Some caves, for example First Cave and Gua Sg. Burung, could be further explored by digging out the sediments.

The three other limestone outcrops reported present in Tabin were not visited during the expedition. They may contain caves, although these caves will be of limited extension due to the small size of the outcrops.

Sites of archeological interest

Some of the big chambers with flat mud floors could contain archeological information. As the area and the caves are rather inaccessible and the caves have been affected by large collapses in recent time, big findings are not very likely. The most promising caves would be Gua Tung Hap, The Silo, The Amphitheater, The Cathedral and the canyon west of The Cathedral.

Paleoclimatic indicators

Cave formations and sediments are being regarded as some of the most valuable indicators of past climates in the tropics (Gillieson, 1996). They hold records of for example sea level change, temperature and rainfall variations and vegetation composition (pollen).

In the Tabin caves no significant mud deposits were encountered, and only a few stalagmites and stalactites were big enough to contain sufficient information. This, as well as the unstable conditions of the caves, does not place the Tabin caves among the most promising sites for paleoclimatic research.

Potential for Tourism development

The caves could be used for tourism, despite the fact that they are not impressively big. Some of the caves are very beautiful and found in picturesque settings and some contains thousands of bats and insects. The big shafts are very suitable for mild adventure and rappelling. Some unstable boulder slopes, however, have to be stabilized prior to any tourism development in the area. None of the caves are easily reached and therefore cannot be visited by weak or elderly people. To make plank walks or in other ways improve the accessibility of the caves is not feasible. 

Due to the absence of edible birds nests, the caves have no economic value at present, and a future development should be able to avoid major confrontations with the locals regarding this matter.

Conclusion

Most of the caves found were located near the northern summit of the limestone hill. They all seem to be part of a once impressive cave system. Numerous collapses have split the system into fragments. This breakdown, which is typical of the final stages in cave development, is a still ongoing process and therefore parts of the area are very unstable. The potential for finding more caves is minimal.

The caves and sinkholes support a unique fauna and flora and should be protected. Furthermore, some caves could hold valuable archeological or paleoclimatic information, and therefore should be left intact for future exploration. Adventure tourism is an option for development. However, precautions have to be taken due to the unstable nature and remote location of the limestone. 

Acknowledgement

We would like to thank all the people from Universiti Malaysia Sabah, Wildlife Department, Kg. Tidong and Kg. Dagat for their logistical support throughout the expedition. Furthermore, we would like to dedicate special thanks to Nasrah, Johan and Osman for their patience, helpfulness and invaluable trail cutting and navigation skills. We are very grateful to DANCED, represented by Dr. Axel Poulsen, for making our participation in this expedition possible.

References

Ellis, B.M. (1995) Making a simple cave survey. In: Caving Practice and Equipment, edited by Judson D.. Menasha Ridge Press. Alabama.

Ford, D. and Williams, P. (1989). Karst Geomorphology and Hydrology. Chapman & Hall. London.

Gillieson, D. (1996). Caves: Processes, Development, Management. Blackwell Publishers. Oxford.

Haile, N. S. and Wong, N. P. Y. (1965). The Geology and Mineral Resources of Dent Peninsula Malaysia. Government Printing Office, Kuching, Sarawak.

Ping, L. S. and Kiew, R. (1997). Gazetteer of Limestone Localities in Sabah, Borneo. Gardens’ Bulletin Singapore 49 (1997) 111-118.

Wilford, G. E. (1964). The Geology of Sarawak and Sabah Caves. Brunei Press Limited, Brunei.

 

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