Living with PseudokarstWilliam R. Halliday6530 Cornwall Court

Nashville, Tennessee 37205(615) 352-9204

bhawrh@webtv.net

Abstract

Urbanization is rapidly increasing in some sparsely inhabited “substan-dard” subdivisions on Hawaiian pseudokarst. Because of conduit flow ofgroundwater in lava tubes and lava tube caves, an increasing threat ofcontamination and pollution exists. Yet conduit flow of water in suchpseudokarsts is omitted from conceptual diagrams and models of localhydrology and dye tracing is an alien concept.

The extent of the problem in Hawaii is unknown. In Terceira (Azores,Portugal) much of the water supply of a sizeable town is obtained fromconduit flow through a lava tube cave; municipal water works have beenconstructed in the cave. A “boiling” freshwater spring in the harbor of Hilo,Hawaii, is among several phenomena suggesting similar flow. Some Hawai-ian lava tube caves contain still-water clay deposits; others have sorted tounsorted heterogenous streamfill. Thus, both steady state and flood pulseflow must be considered.

Kaumana Cave is suggested as a model site for study. It contains garbagedumps including automotive wastes and pesticide containers in an area thatperiodically floods to the ceiling. The resurgence of its floodwaters is unknown,and input and output through various feeder cracks is highly dependent onvolume of rainfall. A piping conduit may exist beneath the cave.

Introduction

Public health aspects of groundwater flow inkarstic conduits are a common topic at nationalcave and karst management symposia. Recentinvestigations in Hawaii and elsewhere indicatethat conduit groundwater flow in volcanicpseudokarsts is a cause for similar concern.This is contrary to conventional wisdom, that

is, that the flow of lava tube caves is flowinglava, not flowing water (Halliday, accepted forpublication). Even a notably authoritative re-cent overview of groundwater tracer dyesmerely commented that “dye transport has ap-parently occurred both through fractures andthrough paleosoil zones (in basaltic lavaflows)” (Aley, 1997).

This mindset has been universal, however.Long ago, the noted geologist James A. Dananoted the essential nature of volcanicpseudokarst, with water “to be found only incaves” (Dana, 1849). Decades ago on the islandof Terceira (Azores, Portugal), municipal wa-terworks were constructed in a lava tubestream cave which drains a small caldera (Fig-ure 1). In Mauritius, “Womens’ Washing Cave”is at the downslope end of a pseudokarsticwindow. In both Utah and Hawaii, local ranch-ers have dammed streams in lava tube caves fordomestic and livestock use.

Stream Downcutting Into Lava Tube Caves

Only a moment’s reflection is needed torecognize that ordinary stream downcutting

Figure 1. Municipal waterworks in a lavatube cave on Terceira, Azores. Photo by

author.

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across the course of a lava tube cave will chan-nel streamflow into the cave it intersects. Fur-ther, that the tubular downslope patterncharacteristic of lava tube caves may be evenmore conductive to conduit flow of water thanthat of karstic caves.

In volcanic pseudokarsts, surface streamstend to sink into cracks before they have anopportunity to cut down into lava tube cavesbut increasing numbers of examples of down-cutting piracy into lava tube caves now are onrecord. Perhaps the most spectacular is in theheadwaters of the Rogue River, Oregon, USA(Figure 2). In Hawaii, the upper level of well-known Turtle Cave (Kau District, HawaiiCounty) is truncated by downcutting by astream which crossed it diagonally. Its lowerlevel contains extensively sorted deposits of atypical turbulent stream.

Downslope Lava Tube Swallets

Numerous other lava tube caves in Hawaii,Korea, and elsewhere contain sorted or un-sorted stream or pond deposits resulting from

surface water naturally channeled into a pre-existing cave entrance. Some of these havebeen incised subsequently by downcuttingwithin the cave. Near Hilo, Hawaii, Pukamauiis a lava tube cave opening on the bank of theWailuku River on the northeast edge of a verylarge pseudokarstic complex. Until it waswalled up, this cave periodically capturedmuch of the water supply of Hilo (Stearns andMacdonald, 1946). The lower kilometer of ApeCave, Mount Saint Helens, Washington, USA,contains two successive tephra “mudflow” de-posits from an eruption about 1,800 years be-fore present; each is about one meter thick.Nearby, some smaller caves carry snow runoff.A few served as conduits for tephra “mudflows”after the 1980 eruptions and at least one “mudresurgence” was observed.

Hawaiian Pseuodokarsts and Their Significance

More than 9,000 square kilometers of “theBig Island” of Hawaii consists of a complex ofvolcanic pseudokarsts. One consists largely ofthe Ailaau Flow Field of Kilauea Volcano,mostly 300 to 500 years old. It contains Kazu-mura Cave (the world’s longest known lavatube cave) and many others. In this largepseudokarst, a total of about 100 kilometers ofcave passages has been mapped to date, withmuch remaining. It is generally considered theworld’s leading area for the study of lava tubecaves. Other speleoiferous pseudokarsts existon Mauna Loa and other volcanos throughoutHawaii. On the islands of Mau and Oahu, tun-nels drilled to tap perched bodies of waterincidentally intersected lava tube caves withrunning streams at considerable depth.

The Ailaau Flow Field Pseudokarst is close tothe city of Hilo, and is the location of increas-ingly populated “substandard” subdivisions,which lack city water, sewers, and other normalinfrastructure. Some wells exist, but mosthomes depend on rooftop water catchment.Many homes lack even septic tank disposal,with pipes conducting raw sewage directly intocracks and lava tube caves. An even denserpopulation with a more fully developed infra-structure lives atop a narrow tongue ofpseudokarst funneling downslope into the cityof Hilo from the northeast side of Mauna Loavolcano.

The most recent flow here (containing Kau-mana and some smaller caves) was in 1881.Nearby caves in older flows are know to extenddown to sea level in Hilo. So do other caves inthe town of Kailua-Kona on the other side ofthe island.

Figure 2. Piracy by downcutting of the RogueRiver into a lava tube cave, Oregon, USA.

Photo by author.

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Unlawful Disposal in Hawaiian Lava Tube Caves

Large dumps of unlawful waste exist inKazumura Cave, Kaumana Cave, LowerUilani Cave, and others throughout Hawaii.Automobile wastes are especially conspicu-ous, but partially emptied pesticide cans andmedical wastes also have been identified.The garbage dumps in Kaumana Cave areespecially troubling. Multiple dumpsitescontaining pesticide cans and medicalwastes are present in a section which floodsto the ceiling, and floodwaters have distrib-uted some of the waste downflow. Further,raw sewage has been reported in a remotersection of the cave beneath Kaumana Village(an up-slope suburb of Hilo), as in severalother “Big Island” lava tube caves. Duringextreme flood pulses, groundwater burstsfrom the lower entrance of this cave andinvades a subdivision built atop what wasonce the lower 500 meters of the cave. Atother times, the resurgence of its floodwa-ters is unknown.

Basic Hydrogeology of Hawaii Island Pseudokarsts

Several recent investigations indicate thatthe volcanic pseudokarst of Hawaii divergeconsiderably from the traditional Ghyben-Her-zberg freshwater lens concept (Izuka and Gin-gerich, 1998; Fischer et al., 1966; GeorgeWilkins, quoted in Hastings, 1989; Smith,1999; Doty, 1980 et al.). Where no conduitexists, the porosity of various volcanic bedsresults in considerable compliance with thismodel. Several types of impervious structures,however, form local barriers to groundwaterflow, both horizontally and vertically. Espe-cially important horizontal barriers are dense,unfractured expanses of pahoehoe basalt witheffects somewhat comparable to those of chert,shale, and sandstone layers in limestones. Asfor vertical or steeply tilted barriers, more orless impermeable dikes trap discrete bodies ofmeteoric water on the flanks of various vol-canos. All these structures are unrelated toconduit flow unless piping has occurred longthe upper surface of dense pahoehoe basalt.The islands are tectonically and isostaticallyactive, however. Cracks up to one or two me-ters wide are locally very important in directingand expediting underground flow at velocitiesapproaching those of conduit flow. Compara-tively small tectonic cracks serve as feeders anddrains for streams in lava tubes.

Further complexity in groundwater flow onthe Big Island is evidenced by two major con-fined aquifers of considerable thickness. Bothconduct large volumes of rainfall from pointshigh on Mauna Loa volcano. They extenddownslope beneath Hilo and some of its south-ern suburbs to deep, ill-defined submarine re-surgences. The lowermost was discovered onlyrecently, at a depth of nearly 300 meters. Whenit was intersected by a test well, hydrostaticpressure caused an artesian flow of 10,000liters/minute (Smith, 1999). The degree ofmissing of groundwater carried in lava tubeconduits with these deep aquifers is unknown.

Basal springs of Hawaii Island especially di-verge from the simple Ghyben-Herzberg lensmodel. Instead of diffuse resurgence at sealevel, bubbling springs are numerous (Stearnsand Macdonald, 1946). Many discrete freshwa-ter plumes extend seaward atop the ocean, asfar as 400 meters (Fischer et al., 1966). Somecomparatively small plumes are approximatelyaligned with Kaumana Cave, but much largerresurgences exist about one kilometer farthersouth, in the Waiakea Pond-Wailoa Streamcomplex. This complex discharges approxi-mately 500 million liters/day into one section

Figure 3. Garbage dump in Kaumana Cave,Hawaii. Photo by author.

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of Hilo Bay—a first magnitude spring. In itsouter channel is a large upwelling “boil” ofwater, which appears to emerge from themouth of a conduit of some type. Also impres-sive is Ninole Springs at Punaluu, downslopefrom a speleoliferous pseudokarst of MaunaLoa volcano. This spring complex is estimatedto have a discharge of 60 to 75 million liters/day(Martin and Pierce, 1919). Here, the largestsprings emerge from lava tubes (Stearns andClark, 1930; Stearns and Macdonald, 1946). Atsea level, discharges downslope from theAilaau pseudokarst, volumetric estimates aremore difficult, but large volumes clearly re-surge here also. It is surprising that conceptualdiagrams and models of regional hydrogeologyomit lava tube and other conduit forms ofgroundwater flow. References to dye tracinghere apparently are nonexistent.

Hydrology of Kaumana Cave

Kaumana Cave is an extensive, largely uni-tary lava tube cave located on a moderate slopein the upland suburbs of Hilo. About 2,200meters have been mapped to date. An addi-tional 500-meter section is known to have beendestroyed by subdivision constructiondownslope from Edita Street. Considerablymore cave exists upslope from the mappedsection, partly underlying Kaumana Village.Raw sewage has been reported entering thissection of the cave. Much as in the case ofdendritic karstic cave systems, still fartherupslope is a recharge area, typical in the ohiarainforest at this elevation (Doty, 1980). In theupper end of the mapped section, floatabledebris is stuck to the ceiling, indicating exten-sive flooding of this part of the cave. In aroomier area just downslope from this area,running water often is heard just beneath theapparent floor of the cave. A piping cave likeChristmas Canyon Cave, Mount Saint Helens,Washington may exist here.

During heavy rainfall (10 to 12 centime-ter/day for three days) several small waterfallsjet out into the cave passage two to threemeters above the floor. They are located a fewhundred feet downslope from the sectionwhich floods completely. They spurt into thecave through cracks in its accreted lining, andappear to emerge from a perched aquifer in-cised by the lava flow containing the cave. Theyform a shallow stream which flows downslopefor about 300 meters, passing beneath the mainentrance sink through a lower level passageformed by a secondary ceiling. Its flow is aug-mented by smaller insurgences through othercracks, near floor level. Loss into other cracks

diminishes its volume and, except during maxi-mum flood pulses, it finally disappears into thecave’s floor. Similar augmentation and lossthrough tectonic cracks have been observedand photographed in Mauritius and in Utah.Except for the maximum flood pulses men-tioned above, resurgences of this stream areunknown.

Significance of Conduit Flow in Hawaiian Lava Tube Caves

In the drier parts of Hawaii Island, conduitflow in lava tube caves some day may providesignificant municipal or agricultural supplies ofwater. Deep confined acquifers, however, cur-rently appear more promising for these. Thepresent focus, therefore, is on public healthaspects of conduit flow—just as in the case ofsimilar flow in karsts.

It thus is obvious that unlawful disposal sitesand raw sewage are potential threats to groundwater quality in parts of Hawaii Island. Also itis obvious that these threats will increase withincreasing population density in certainpseudokarstic areas unless present practicesare altered drastically. But it is not certain thatthese practices are actually causing unaccept-able harm to Big Island residents. Nor is itcertain that even today’s uncontrolled popula-tion growth will inevitably impact groundwaterquality to an unacceptable level. The dilutionfact in the Ailaau pseudokarst and the MaunaLoa deep aquifers is enormous. Admittedly,Hilo Bay is polluted, and swimming is discour-aged. Where swimming is common in otherfreshwater plumes such as Ninole Springs,there are anecdotal reports of a high incidenceof otitis externa and its complications. But theincidence of leptospirosis actually seems to belower from well water than from rooftop catch-ment. Perhaps it is fortunate, however, that the

Figure 4. Waterfalls, Kaumana Cave,Hawaii. Photo by author.

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apparent drainage of the Aillaau pseudokarst isto a section of coast unsuitable for swimmingand lacking in wells.

Management of Conduit Flow in Big Island Pseudokarsts

The usual laws for the protection of ground-water exist in Hawaii, but the General Plan forHawaii County (1990) does not include protec-tion of groundwater (nor caves) and these lawsare generally unenforced.

The Hawaii Chapter of the National Spe-leological Society has proposed two ap-proaches to this problem. On one hand, it hasproposed a series of new provisions in the2000-2009 General Plan. These new sectionswould provide a priority for protection ofcaves, pseudokarst, and groundwater, withzero tolerance of raw sewage and toxic andhazardous wastes. Further, it has proposed aconference to bring together human resourcesin the relevant fields to clarify actual threats topublic health and to recommend solutions.

In September 1999 the Commission on Vol-canic Caves of the International Union of Spe-leology commended the Hawaii Chapter for itsleadership in this important area.

Conclusions

Conduit flow of water in some volcanicpseudokarsts differs only quantitatively fromthat in karstic terrains and has the same publichealth implications. Studies of types long estab-lished in karstic terrain need to be imple-mented in large areas of Hawaii. Both steadystate and flood pulse flow must be considered.Titles of symposia on management of caves andkarst should be expanded to include this addi-tional area of concern.

References

Alley, Thomas. 1997. “Dyes Don’t lie: PracticalKarst Hydrology.” In: Tamin Younos et al.,editors. Proceedings, Karst-water Environ-mental Symposium, October 30-31, 1997.Roanoke, Virginia. Virginia Water ResourceResearch Center, Virginia TechnologicalUniversity, Blacksburg, Virginia.

Dana, James D. 1849. United States ExploringExpedition during the years, 1838, 1839,1840, 1841, and 1842, under the command

of Charles Wilkes, USN. Volume X: Geology.Philadelphia, printed by C. Sherman. p 160.

Doty, Robert D. 1980. “Groundwater Condi-tions in the Ohia Rainforest, Near Hilo.” In:Clifford D. Smith, editor. Proceedings of theThird Conference on Natural Sciences, Ha-waii Volcanoes National Park, June 4-6,1980. Cooperative National Park ResourcesStudy Unit, University of Hawaii at Manoa,Department of Botany, p 101.

Fischer, William A. et al. Fresh-water Springs ofHawaii From Infra-red Images. U.S. Geo-logical Survey Hydrologic Investigations At-las HA-218.

Halliday, William R. (accepted for publication)“Conduit Flow of Water in VolcanicPseudokarsts.” In: Giuseppe Licitra, editor.Proceedings of the IX International Sympo-sium on Vulcanspeleology, Catania, Sicily,September 1999.

Hastings, Barbara. 1989. “Untapped Big IslandWater Believed Flowing into the Sea.” Hono-lulu Sunday Star-Bulletin and Advertiser,December 20, p A-1, c. 1.

Izuka, Scot K. and Stephen B. Gingerich.1998."Estimation of the Depth of the Fresh-Water/Salt-Water Interface From VerticalHead Gradients in Wells in Coastal and Is-land Acquifers." Hydrogeology Journal, Vol-ume 6, p 365.

Martin, W. F. and C. H. Pierce. 1919. WaterResources of Hawaii, 1909-1911. U.S. Geo-logical Survey Water Supply Paper 318, p355.

Smith, Dave. 1999. “Research Well Unearths aFew Unexpected Discoveries.” Hawaii Trib-une-Herald (Hilo, HI). May 25, p 1, c 5.

Stearns, Harold T. and William O. Clark. 1930.Geology and Water Resources of the KauDistrict, Hawaii. U.S. Geological SurveyWater Supply Paper 616, p. 176.

Stearns, Harold T. and Gordon A. Macdon-ald. 1946. Geology and Groundwater Re-sources of the Island of Hawaii. Bulletin 9,Territory of Hawaii Division of Hydrography .p. 363.

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