OUCC Proceedings 11 (1983)

Borneo 1983 - Some Karst in the Penrissen area of Sarawak

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Martin Laverty

On the NE coast of the island of Borneo, one degree north of the equator, there is a sinuous band of limestone forming karst towers, hills, and plains. En the spring of 1983, a group of five cavers visited a part of this area adjacent to the Penrissen Road. This road is one of the oldest in Sarawak, having reached the longhouse village of Segu (alias Bunuk), 21 miles south of the capital, Kuching, in 1898. Despite this, only two caves were recorded as having been explored and surveyed (Wilford, 1964).

Geological background

The limestones of the Bau-Serian outcrop belong to the Upper Jurassic - Lower Cretaceous Bau Limestone Formation (Wilford & Kho, 1965; Wolfenden, 1965). They originated as reef limestones (Coo & Lau, 1-7) and have been the subject of several undergraduate field studies (Bait, 1980; Jantan, 1969) and of an intensive resurvey by Victor Hon of the Malaysian Geological Survey Department, whose new map and report are awaiting publication. Preliminary reports give son~ indication of the work involved (1-2; 1-3). Intrusive rocks appear to have had a considerable effect on the Bau area, but are not important in the Penrissen area. However, the debris of considerable extrusive volcanic activity in the form of large amounts of ashfall-derived allophane deposits is revealed in large amounts in the cave sediments. These very closely resemble those found in the two major karst areas of northern Sarawak, Niah and Mulu (Laverty, 1982). The source of this material is unknown, but there are several distinct possibilities:

  1. Sarawak is within reach of ash falls from volcanoes in both the Indonesian and Phillipine island arcs, and incidences of such falls have been recorded (e.g. Everett (1878) evidently records the Tambora eruption of 1815 as "..according to native testimony slight shocks are by no means rare, and a severe one is particularly held in remembrance, which took place seventy or eighty years ago, and was accompanied by a rain of ashes".). A problem could be that the prevailing winds would not always bring the ash over Sarawak, but there again, the winds may have been different at the time.
  2. During the late Pliocene and early Pleistocene, there were extrusive volcanoes in central Sarawak which could be the source (Kirk, 1963). Being nearer, this could be more likely.
  3. Harrisson (1961a; 1961b) began investigating volcanic ash beds in the Niah Caves, in association with Shell geologists. No further reference is made until, in 1-2, while discussing the radiocarbon dated lavas of G. Kinabalu, he refers to 'equivalent volcanic ash sills [sic] ...in the Niah Caves'. This correlation would appear unlikely. No supporting evidence on the stratigraphy is known, and Harrisson assumes the deposits to be aeolian whereas Wilford (1963, 173) points out that they are more likely to have been washed into the caves through cracks and fissures.

The solution of this problem will probably require chemical and mineralogical analysis, dating, and perhaps quantification of the deposit to determine whether any distribution pattern can be discovered.

The cave sediments as a whole also show a markedly similar sequence to those in Mulu (Bull & Laverty, 1981), with gravels overlain by silts and sands (the Cricket Muds of Mulu). The gravels are rarely seen, at least in part because corrosion has been so intense that they are now represented by mere ghost images and have physically become silts. With any disturbance their identity would be lost.

Geomorphological background

Climate undoubtedly has an effect on geomorphology. Today, the area has a wet tropical climate (about 4570 mm rain per annum at Kuching), with some monsoonal influence. During the Pleistocene, sea level changes exposed large areas of the nearby Sunda Shelf and are thought to have thereby caused a somewhat drier and more seasonal climate. The limestone surface takes several forms:

  1. Karst plains which tend to be very flat, but intensely corroded into deckenkarren blocks which are revealed when the soil is excavated manually, as at Bau, or naturally by rivers and streams. River beds often give the appearance of new plains at an early stage of development with prominent notches formed at the flood water level, where not obscured by...
  2. Debris slopes of blocks of assorted sizes, sometimes clearly derived from landslides which have left...
  3. Vertical rock faces, above which are...
  4. Intensely corroded bare rock surfaces, at all scales from rillenkarren to large karst depressions.

Directed phytokarst (Bull & Laverty, 1982) is found in this area, especially in the more inaccessible parts of cave entrances, where visiting feet have not crushed this most delicate and fragile land form into dust.

Biological background

There were no biologists on the trip, so only cursory notes are possible on the wildlife encountered in and around the caves. The vegetation on the limestone slopes can be assumed to be little disturbed, except by what appear to be not infrequent fires on the upper slopes and by cultivation on some of the less rugged and more soil-rich lower slopes. Progress through this natural limestone forest is generally fairly easy; indeed the vegetation more often assists than impedes progress. Virtually all non-limestone areas are either under cultivation or are occupied by secondary forest. These areas are veritable jungle. Little is to be seen alive by the casual visitor - we saw and despatched one snake (as it happens, a fairly harmless Wagler's pit viper) and not much else. Much more is to be heard, especially if a camp is made in the forest.

In the caves, granny frighteners are much in evidence. Rats caused the exploration of at least one passage to terminate early, and centipedes also caused considerable consternation when sighted. Whip scorpions (tailed and tailless) were not uncommon, but did not seem very menacing, being rather like the cave crickets in size and colour. Small white millipedes seemed common in some places, especially -around the rotting bamboo, swift and sometimes bat guano which accompany swifts' nesting areas. Small red-brown cockroaches are also sometimes to be found here. Bats were not present in very large numbers, the birds' nest swifts being more obvious by their loud clicking and sometimes poor navigation. Despite this, we saw no evidence of cave snakes.

Human and Historical Background

The Sarawak River delta has been shown by archaeological work to have been in trading contact with the ancient oriental civilisation for well over a millennium. The basis of this trade was the produce of the hinterland now known for administrative purposes as the First Division: the first part of Sarawak taken over by the Brooke dynasty in 1841. The produce included bird's nests, so it is certain that some caves must have very long histories of exploration. The cave entrances have also provided shelter, as shown by excavations and also by observation of shell middens of freshwater snail shells broken for eating. It is probable that these caves have been explored over a longer time span than perhaps any others, with the possible exception of the European painted caves.

The earliest recorded explorations date from 1842 when James Brooke and his associates, like Capt. Mundy, visited a cave in C. Tubband (Keppel, 1846) (Mundy (1848) refers to it as C. Tabong), and from other explorations by Brooke's officers such as Hugh Low. Low's exploration of a cave in Gunong Rumbang in 1845, near a place he called Sempro, is of particular interest here, as the first group of three on our trip tried to find and survey this cave from the village of Emproh. Low (1848) records how the cave passes right through the mountain, and carries a stream from the far entrance. Later, probably in 1852, Spenser St John (1862) appears to have visited the same cave and also succeeded in visiting an upper bird's nest cave, which Low couldn't reach due to the poor state of the route which 'only a Dyak can climb' and which was said to be booby trapped to deter nest robbers. Wilford (1964) records St John's, but not Low's, visit, but did not survey the cave or visit it himself. This is probably because the approach to the closed depression is much easier through the cave from the natural highway of the river than from the new road and an ancient path which, after passing through rubber and fruit groves, patches of vegetables and bananas, ended in a near-vertical padi field. Without, at that stage, a hefty parang, we beat a retreat.

In 1879, A.H. Everett was encouraged by A.R. Wallace and by C. Lyell, who had discussed such a project with Beccari in 1865, to explore the caves of Sarawak in search of the 'missing link'. He was funded by the Royal Society and the British Association for the Advancement of Science. Of course, he didn't find it, although he might have collected what later became the 'Piltdown jaw' (Matthews, 1981); neither of his published reports (1879; 1880) give a detailed indication of where he looked.

Little has been written of local traditions, ownership, or activity in the caves. The local people seem to give loose ownership of the right to collect bird's nests to a few people, but do not mind others if they do not interfere. As for tradition, the traditional religion is animist and so some form of sacrifice to the spirit of the cave is in order on entering it. Cigarettes seemed popular, and we gave bananas. These seemed quite acceptable, and disappeared quickly.

Speleological background

Local cavers, as has been indicated above, have known parts of many, if not all, of the caves for many years. Evidence of visits by literate cavers is abundant in the graffiti - some in English, but most in Chinese ideograms, plus assorted arrows and pictures. Glass bottles are quite common and some appear to be quite old: square -sectioned bottles originating from Rotterdam were the most distinctive. The other evidence of past visits is in the various aids left in the caves. Bamboo is the commonest material and is used both to assist on climbs and to probe for bird's nests. In one place, steps had been hacked out of a stal boss, and in another a projecting flake of rock had been broken off to provide an easier route through a section of cave.

Lighting today is usually by hand-held electric torch, but a flaming torch generated by wicking paraffin up a rag stuffed into a bottle is not uncommon. A more ethnic version of this is to use a bamboo cylinder as the paraffin container. The records of the Sarawak Museum show that an attempt was made to introduce carbide lamps at the Niah Caves in the 1920s, but the recipients preferred to use resin or beeswax candles tied on to a bamboo in the caves and reserve the bright carbide lamps for nocturnal hunting trips in the forest outside. Nowadays carbide is increasingly hard to obtain (we spent several days not finding any in Kuching and eventually located a small supply in a hardware store in Bandar Sri Aman), and the lamps are advertised for sale to rubber tappers, or Thai tin miners. Geological survey investigations seem to have used torches and paraffin lamps for illumination, judging by the photographs in Wilford's (1964) book. Future visitors might be best advised to use electric lighting; mains electricity may not always be available, but generators are not uncommon, and some modern lamps can be charged from car batteries which can be found powering TVs even in areas without roads (e.g. at Temurang).

Medical aspects

An important part of our early plans had been to carry out some medical projects concerned with caving in the area. All but one of the 1978 Mulu cavers had suffered some form of fever which was not fully diagnosed. In 1980/81, four cavers suffered fevers and one a severe allergic response, apparently to guano. Literature references were also found to a case of leptospirosis (attributed to bat and swift guano) affecting a European in a cave at Bau (Harrisson, 1968), and another reference indicated the presence of the histoplasmosis fungus in Sarawak, though not in caves (Harrisson, 1965). Together with the possibility of rabies and the danger of falls and cuts by sharp or jagged limestone, there seemed to be abundant material for further investigation. Do the bird -nesters suffer from problems not affecting their fellows who remain outside the caves? Is everyone histoplasmin-positive through permanent exposure? Could foreigners be exposing themselves to specific medical hazards by visiting the tourist caves at Bau, and if so, were the authorities aware of the danger? Without the assistance of local medical staff we did not attempt to pursue these questions, except for supplying Dr T.W. Tinsley of the NERC Institute of Virology at Oxford with a guano sample from T Baan. This proved devoid of rhabdoviruses, an encouragingly negative epidemiological result, but all the questions remain very relevant. As to the health of the participants on this trip, one member suffered from a depressing allergy to all the antimalarial drugs he tried; one endured oditis externa (earache), probably due to too much swimming; and another returned to the UK not only with typhoid, but also dysentery (probably not originating in Sarawak, where there was a cholera outbreak). He also left the UK with diarrhoea!


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