Karst in Arid Australia Nicholas White

123 Manningham St, Parkville, Victoria, 3052 AustraliaTel/FAX: 61 3 9328 4154

nicholaswhite@netspace.net.au

Abstract

This paper presents an overview of some of Australia’s arid and semiaridkarst and its management. Australian climatic conditions are characterizedby exceptionally high rainfall variability especially in areas of irregular lowrainfall. Definitions of arid are an important component when discussingsuch karst development and management.

The areas discussed include the arid karsts of the Nullarbor Plain andCape Range. The arid monsoonal areas of Northern Australia, include theChillagoe Karst, the Camooweal Karst, the Katherine Karst, the Bullita Karstof Gregory National Park, which contains Australia’s longest cave, and thekarst of the Western Kimberley Region.

This paper discusses the effects of arid climates on the processes of karstdevelopment and the effects on present cave biota. Australia is a Federationof States. The States each have their own legislation governing the use,protection, and ownership of land. The effects of this will be discussed inrelation to land tenure and karst protection in these remote and sparselysettled areas of Australia. In particular, many of the caves and karst areashave traditional aboriginal uses such as for occupation and for spiritualpurposes. Some caves and many shelters and overhanging cliffs have rockart engraving and painting. In recent time, Native Title and indigenous landuse have had to be taken into account by management agencies and by cavegroups desiring access to sites for recreation or scientific purposes.

Introduction

Australia is a drycontinent with ex-treme variability inrainfall. Many of itskarst areas reflectthis aridity. The aridkarsts of NorthernAustralia all exist inwhat is known as theWet Dry Tropicscharacterized by aSummer Monsoonfrom December toMarch. Travel andcave exploration isprecluded duringthe wet season.These areas have in-tense but variablerainfall during thiswet season but prac-tically no rainfall forthe balance of theyear with a very high

Figure 1: Australian karst areas, showing climatic zones. Zone IIMonsoonal wet-dry tropics; Zone III Arid; Zone IV Mediterranean-

winter wet/ summer dry.

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evaporation potential. In contrast, Cape Rangeon Northwest Cape in Western Australia andthe Nullarbor Plain are arid with less than 250millimeters of rain per annum. This paper willrestrict itself to the karst at Bullita in GregoryNational Park, Northern Territory, and thesemi-arid karst of the Nullarbor Plain whichbridges the Western Australia and South Aus-tralia borders on the Southern Coast of Austra-lia (Figure 1). These two karst areas will be usedto exemplify some of the contrasts in manage-ment of karst areas in Australia and also be-cause they have very active speleologicalinvestigation programs.

Gregory Karst

The Gregory Karst is located within the Gre-gory National Park and is some 45 kilometerssouth of Timber Creek. The karst is on theboundary of the desert to the south and thewetter area to the north, which is subject to atropical monsoon season from December toMarch. Most of the rainfall occurs during thisperiod and total annual rainfall is about 600millimeters. The evaporation potential is about2,500 millimeters per annum. The GregoryKarst is in PreCambrian dolomite that has beenexposed since the Tertiary as a result of thedown cutting of rivers across the Victoria RiverPlateau. The karst is exposed along the EastBaines River. The only macrofossils in the for-mation are stromatolites. Caves occur in theSupplejack Member of the Skull Creek Forma-tion. They are network maze caves in grikefields with numerous entrances at both theedges of the limestone and there are manyskylights along thegrikes (Figure 2).The relief of the lime-stone is about 60 me-ters.

Modern knowl-edge of caves in thearea followed a Brit-ish led expedition in1988 (Storm andSmith, 1989). Fol-lowing this trip, theCanberra Speleologi-cal Society has con-ducted trips to thearea for two or threeweeks each year dur-ing June and July, thewinter period. Localcavers from the TopEnd SpeleologicalSociety also conduct

trips and have explored and mapped numer-ous caves. The karst extends for some 20 kilo-meters north-south and up to one kilometerwide. There are many outlying exposures,which have not been investigated to date andexposures along other rivers outside the Gre-gory National Park. The total length of knowncaves now exceeds 150 kilometers. The BullitaCave System is currently the longest cave inAustralia at 81 kilometers. Each year the ex-plored and surveyed length of this cave systemis increased in length by three to ten kilome-ters.

The aboriginal inhabitants of the area knewcaves in the Gregory Karst. Shelters were usedfor occupation and many have associated caveart. In only one instance has rock art beenfound well within a cave, all other art is inoverhang, rock shelter, and entrance locations.The art consists of ochre paintings of animalsand mythical beings. Many of these sites haveimportant cultural and spiritual significance.Cave exploration has led to the discovery ofnumerous important sites, which are docu-mented, but the locations are made knownonly to National Park personnel. Many of thesesites are vulnerable to damage, particularlynatural weathering. Only one or two sites arevisited frequently by tourists. No photographsof these are included in the paper due to re-spect for aboriginal sensitivities.

The caves have not been investigated bio-logically although bats are known to roost insome of the caves during the wetter times ofthe year. Vertebrate fossil deposits have notbeen found. Many of the caves flood in partduring the wet season. Given the richness of

Figure 2: Cave passage in Bullita Cave with fig tree roots.

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fauna found elsewhere, for example CapeRange and Chillagoe, there is potential for im-portant biological work.

The area was a leasehold cattle station fromthe 1920s until the 1980s when it was gazettedas the Gregory National Park which is adminis-tered by the Northern Territory ConservationCommission. To date, development of the Parkhas been limited; access is by a two-wheel driveroad from Timber Creek to Bullita but all otherroads require four-wheel-drive vehicles. Caveexploration has been conducted with permis-sion from the Conservation Commission. Cas-ual cave exploration is not encouraged sincethe karst is rugged and remote and climaticconditions are harsh. As yet there is not anoperational management plan for the Park al-though the two caving clubs have contributedinformation and advice for planning purposes.

Nullarbor Plain

The Nullarbor Plain is one of the largestlimestone regions in the world at about200,000 square kilometers in area. It is a flat-ly-ing, shallow marine plain of Miocene age over-lain with some Pleistocene dunes particularlynear the coast. It is so named because of thelack of trees (null arbor). All the northern partof the limestone is virtually without trees andonly has saltbush and grasses up to one meterin height. The climate is arid to semi-arid withrainfall of 260 millimeters per annum close tothe coast but only 180 millimeters per annumat the railway on the northern edge of theexposed limestone. The Nullarbor Plain has no

surface streams and little relief. A number ofdeep caves exist. These occur at the bottom oflarge collapse dolines and a number of thesecaves intersect the watertable at about 90 me-ters (Figure 3). It was not until 1970 that suc-cessful cave diving trips were undertaken withmodern scuba gear. Cocklebiddy Cave is 6,260meters long; with about 5,200 meters under-water, the longest cave dive in the world. Otherlong caves include Mullamullang Cave (12,000meters) and Old Homestead Cave (8,000 me-ters). The other feature of the plains are the“blowholes” so named because they breathe inand out depending on atmospheric pressure.There are currently about 1,000 of theseknown. Many are very short but some are quiteextensive. They are generally less than 20 me-ters deep. They are mainly concentrated on thebroad, low ridges (two to five meters) about theplain. A recent innovation has been to locatethese using an ultralight aircraft to positionsites by GPS and then systematic explorationusing the GPS locations to find entrances. Mostof the deep caves have probably been discov-ered as these were known from local informa-tion followed by systematic visiting of all siteson aerial photographs of the area in the late1950s to early 1960s (Dunkley and Wigley,1967).

Numerous troglobytes have been found inthe caves. Some of the caves have extensivevertebrate fossil assemblages, which have onlybeen minimally examined to date. There hasbeen considerable geomorphic investigation ofthe Plain and its caves. Aboriginal use of theplain involved hunting and travelling routes.Caves were used as a water source (high inMgSO4), for occupation, for mining of flintnodules, and for cultural purposes. Some ofthe caves have etched engravings and othersochre paintings.

The Nullarbor forms part of Australia’s my-thology. It was the barrier between WesternAustralia and the eastern states and was notcrossed until 1840 to 1841. It was not until thetelegraph line was constructed (1877) close tothe coast and the railway further north that theplain became more accessible. Both WesternAustralia and South Australia leased the landfor sheep and cattle grazing. In South Australia,all the leases have been revoked and the lime-stone portions are now in National Park or onaboriginal land. In Western Australia, a numberof grazing leases have lapsed but on the richer,higher rainfall areas near the coast there arestill leasehold cattle properties. Some years agoplanning to have the whole of the Plain putforward as a World Heritage Area was initiatedbut this lapsed due to the politicization of such

Figure 3: Lake in Weebubbie Cave withwater supply pipe, subsequently removed.

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initiatives. The caves are thus inadequately pro-tected and there is little management on theground. This is despite the Plain and its cavesbeing outstanding in a national and interna-tional context.

Most caving is conducted responsibly andonly a couple of the caves receive very manyvisitors. Amongst these is Mullamullang Cavewhere damage in the Easter Extension to theSalt Cellars and “Coffee and Cream” sections isexcessive. The rare troglobitic spider, whichonly occurs in and around the “Dome,” 4.5kilometers into the cave, is extremely vulner-able to disturbance and collecting. At onestage, it was thought that it was extinct butmore recently active webs have been observed.This spider is at the end of a very tenuous foodchain at the far end of the cave.

Caving trips to the Nullarbor are generally ofan expedition nature for several weeks. Caversneed to be self-sufficient for all needs includingwater. Rescue services are thousands of kilome-ters away. This is particularly relevant to divingparties where decompression chambers arevery long distances away.

Landscape Fragility

Australia has an old landscape. Its soils areshallow. There has been little or no rejuvena-tion through uplift and other mechanisms.Abuses of land from overgrazing and the in-troduction of exotic plants and animals havecaused regional extinctions of many species.On the Nullarbor rabbits, foxes, and cats havereduced the populations of many animals.Grazing by sheep and cattle have similarlyreduced the condition of native pastures. Ar-eas that are not now subject to sheep andcattle pressure are reverting to the originalcondition but there will remain a legacy of areduced number of vertebrate species on theNullarbor. It is not known whether thesechanges on the surface have endangered cavebiological populations due to changes infood chains. There appear to be a number ofbat roosts that have not been used for manyyears. It is not known whether these reflectthe changes of surface tenure and usage orare part of much longer term responses toclimate change.

Underground conditions on the Nullarborreflect the arid environment. Caving contrib-utes to damage, particularly surface trampling.Natural processes of rejuvenation such asflooding, as occur in higher rainfall karsts, aremost infrequent in arid karsts and, except forwind deposited sand and for fretting from thewalls, damage from trampling lasts a very long

time. Many calcite speleothems exhibit damagedue to salt wedging and it is not uncommon tosee piles of broken formations shattered by thissalt wedging. In some places quite magnificenthalite and gypsum speleothems occur (Figure4). There is no evidence of deliberate vandal-ism but problems of track widening and indis-

criminant tracking occur.In Gregory National Park, there are less

dramatic changes than on the Nullarbor;however, there are exotic weed infestationsand feral horses and donkeys continue toaffect vegetation recovery. The caves have nothad very many visitors and tracking or otherdamage is minimal. Visits to the cave art sitesare limited. Problems may emerge if caveusage were to go up. The greatest problemfaced by management would be if inexperi-enced cavers got lost in what are very exten-sive caves.

Conclusions

Arid karsts in Australia are very fragile andthe caves need careful management to preventtrampling of floors particularly. Mechanisms oftrack marking are in use in many sensitivecaves; however, the single most pressing needis for deliberate management of the deep caveson the Nullarbor Plain. The Nullarbor Plain inWestern Australia needs legislative protectionand more focussed management attention. Forthe South Australian section, more on-groundmanagement would prove beneficial. The Plainis now visited extensively, particularly to watchwhales at the Head of the Great Australian

Figure 4: Halite salt formation, EasterExtension, Mullamullang Cave.

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Bight. Also visitation by both cavers and cavedivers results in change within the caves de-spite subscribing to minimal impact cavingcodes.

At Bullita, some long term managementstrategies need to be formulated to contendwith people with karst interests, be they casualvisitors on “Round Australia” trips or moreserious speleological visitors. The present ac-cess through very restricted access permits can-not continue for long, given that the BullitaCave System is now the longest cave in thecountry.

Acknowledgments

Many thanks to Ken Grimes for the use ofFigure 1 showing karst areas in Australia.

References

Dunkley, J.R., and T.M.L. Wigley, 1967. Caves ofthe Nullarbor: A Review of Speleological In-vestigation in the Nullarbor Plain, SouthernAustralia. Published by Sydney UniversitySpeleological Society and Cave ExplorationGroup (South Australia), 61 pages.

Dunkley, J.R., 1993. The Gregory Karst andCaves, Northern Territory, Australia. Pro-ceedings 11th International congress of Spe-leology, Beijing, China pp17-18.

Storm, R. and D. Smith, 1991. The Caves ofGregory National Park, Northern Territory,Australia Cave Science 18, 91-98.

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