CURRENT STATUS OF THE EWA KARST, HONOLULU COUNTY, HAWAII

William R. Halliday

(Pre-printed from The Cave Conservationist - a future issue with a past date that will be out in late February 1998)

Ewa Karst Map

Figure 1. Map of Ewa Karst, base geology by Stearns and Vaksvik, 1935 modified by unpublished data of Board of Water Supply, courtesy Chester Lao. Cartography by Carlene Allred.  To see where this fits into the region, look at these maps from the Web.

Contents

1) Introduction

The Ewa Karst is the largest of several karsts on the well-populated island of Oahu, yet one of the least known (Halliday, 1994). Its exact dimensions are uncertain because geological maps show considerable upslope areas as alluvium and some shore areas as sand. However it clearly covers at least 50 km2 in the southwest corner of the island of Oahu (Figure 1). It is a semitropical littoral karst formed on porous, permeable algal and coralline reef deposits formed during at least three high stands of sea level (Figure 2), perhaps with a higher content of sand-sized clasts of foraminifera than contemporaneous Caribbean deposits (Chester Lao, written communication, 1997). The type locality is at Waimanalo, at the east end of the island (Stearns and Vaksvik, 1935). From present sea level these calcareous formations rise to an altitude of about 20 m. Tidal fluctuations extend inland from the shore line but freshwater at least 10 m deep has been found within 2 km of the shore, floating on salt water in the form of a Ghyben-Herzberg lens. Hillsides and mountains upslope from the karst are volcanic (Figure 3). Presumably their runoff is acid, but no dissolution conduits are known in the upslope part of the karst. Some artesian flow is said to be present, confined by clay layers (Chester Lao, oral communication, 1997). The U.S. Geological Survey Ewa Quadrangle shows numerous sinking streams and closed depressions within the Karst. Some of the former are artificial: the result of past water diversion for farming, ranching and domestic use. Some of the depressions are manmade also. Most of the land surface of the karst has been subjected to more than a century of extensive reworking by man.

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Figure 2. Stratigraphy of carbonate formations near barge harbor, exposed in quarry wall. WRH photo, July 1997.

Figure 3. Eva Karst near barge harbor in 1977, looking north toward south end of Waianae Mountains, with vegetation and karstic surface bulldozed. Photo by Ben Atnoi, courtesy Alan Ziegler.

2) Environmental history

Despite its impressive extent and archaeological and palaeontological values, the Ewa Karst is almost entirely unknown to karstographers and speleologists. The late James Quinlan, former hydrogeologist of Mammoth Cave National Park, served as consultant on one project, but my conversation with him shortly before his death led me to believe that he evaluated his study area in terms of classical karst, not sea level karst. His report is not generally available, but he is understood to have noted nothing of significance. In 1955, the late Harold S. Palmer (Professor of Geology at the University of Hawaii) told me he had seen a meter-long stalactite said to have come from a cave in the Ewa Karst (Halliday, 1955, 1958). Extensive bibliographic and some field investigations have yielded no information about this cave and it is not known if it still exists. In 1970, Macdonald and Ahhott mentioned the presence of small caves in calcarenite and aeolianite in this and several other karstic localities (Macdonald and Abbott, 1970) but did not amplify. In July and August 1977 Morganstein and Child conducted a "geological and geo-archaeological reconnaissance in the form of examination of several sinkholes (sic) at Barbers Point" (Hawaii Marine Research, Inc., 1978). They recognized the existence of karst, but their report contained such statements as:

With regard to land utilization, karst regions are generally unfavorable today because of their undulating and dangerous topography...

Their term for a sizeable phreatic dissolution cave accidentally opened in 1973 during quarrying operations ("Site B6-139") was ''unmodified wet sink-cave". Quarry operators deliberately tried to fill this cave before 1977 archaeological and palaeontological salvage studies (Sinoto, 1978, p. 45) but it was too large.

Prior to World War II, the principal use of the karst was growing and processing sugar cane, with only small residential communities. Ranching was a smaller industry, in drier areas. For both purposes, native vegetation was destroyed until only tiny remnants remain. Keawe (thorny acacia) was planted as cattle feed. Where not bulldozed in turn, it persists as the dominant vegetation of unurbanized areas. Recent stripping techniques utilize a chain stretched between two bulldozers.

A large naval air station was one of the earlier modern developments on the karst.  Currently it is scheduled for closure. Since World War II, industrial parks, quarries, oil refineries and storage tanks, a barge harbor dredged out of an especially cavernous area, the new, growing city of Kapolei, a controversial lead-cadmium dump (Alan Ziegler, oral communication, 1997) and other developments have replaced the sugar cane which no longer is a profitable crop in Hawaii) (Figures 2,3). Most of this development has occurred without recognition of the special qualities of littoral karat, or appreciation of it. Dredging for the new barge harbor destroyed the most notable cave known in the Ewa Karst without it even receiving a name (Figures 4,5). For unclear reasons, it was rarely even termed a cave and was variously referred to as a "flooded sink", a "wet sink(cave)", etc. It quickly became famous in palaeontological circles because of its content of bones of extinct birds (Figure 6). Then it was destroyed in order to construct the farthest reaches of the barge harbor. "None of the researchers has suggested that the proposed $100 million harbor should be cancelled to save the sites", the Honolulu Star-Bulletin and Advertiser noted (Benson, 1977), and none notified the American cave conservation movement, which was strong and active at that time. Although it contained no archaeological material, this cave is remembered today only by the Bishop Museum archaeological site number "B6-139". The American cave conservation movement learned of it two decades too late.

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Figure 4. Stalactites and stalagmites in destroyed cave B6-139. August 1977 photo by J.K. Obota, courtesy Alan Ziegler.

Figure 5. Swimmers in destroyed cave B6-09. August 1977 photo by Ben Obata, courtesy Alan Ziegler.

Figure 6. Subfossil bird bones from destroyed cave B6-139. August 1977 photo by J.K. Obata, courtesy Alan Ziegler.

3) Some features of the Ewa Karst

Morgenstein and Child (Hawaii Marine Research, Inc., 1978) noted:

. . . the west sink(cave) contains well-formed stalagtites (sic) and stalagmites, some of which are subsurface.

Algal coloration of the high cave aragonite skins indicate that the water levels were at one time elevated above the present mean water table. Various fossil birds are impregnated and cemented with aragonite on the rubble terraces of the cave. The cave was therefore actively precipitating aragonite prior to the birds; arrival, during their entrance into the cave, and during their departure.

They also noted water level fluctuations of 40cm (16 inches) even though the cave is almost 2 km from the shore. However it was left to archaeologist Aki Sinoto to provide details about the cave. He termed it "a unique flooded sinkhole'', and found that it measured 11 m in diameter. Fresh to brackish water filled 2/3 of parts of the cave. A nocturnal marine isopod, blue-green algae, and minute red shrimp (Holocaridinea rubra) were observed but the primary finding was the rich deposit of intact bones of subfossil and-extinct birds (Sinoto, 1978).

Morganstein and Childs examined and described several other karstic features in and near the harbor-to-be: ". . . representative sinkholes . . and two major sinkholes (B6-78 and B6-1OOC)" which they excavated (Hawaii Marine Research, Inc., 1978). B6-78 proved especially important for recent and subfossil mollusca which are excellent indicators of recent environmental conditions (Kirch, 1977). Review of their descriptions, photographs, and maps shows that none of these features were what karstographers or speleologists term sinkholes. Yet their term lives on today, probably with serious adverse environmental effect. Most of them are typical small dissolution pit caves (Mylroie and Carew, l995, p. 60). Nearby is a phreatic dissolution cave of the type called ''banana holes" in the Caribbean (Mylroie and Carew, p. 63). A short distance outside the Morganstein/Carew study area, it is an ovate, overhung cavity about 6 m deep and 10 to 20 m in diameter, partially open to the sky as a result of ceiling instability. It was a habitation site for ancient Hawaiians, with a tall, thin rockpile for entry and egress, a hearth containing a burned bone of an extinct giant goose, and other features. Its surroundings now are fenced off by its owner (Campbell Estate), and retain a near-natural state even if not a pristine one (Ziegler, l990b). On state-owned land nearby, another fenced area contains a much smaller dissolution cave of archaeological significance ("B6-137") (Ziegler, l990b). Unlike "B6-22", much of the land surrounding it appears to have been bulldozed recently.

In addition to these fenced areas, a small plot on the seaward side of Malakole Road is fenced to preserve a small group of specimens of rare and endangered native plants. This area also is on private land; their protection was a specific requirement for approval of development of a large adjoining area of the karst (Alan Ziegler, oral communication, 1997). Coincidentally, this fence also protects a fine group of epikarst features and pit caves to 2 m in diameter. Some extend well below mean sea level. Their water is brown and fluctuates perceptibly with tides. Alan Ziegler has removed large quantities of rubble from some of them, under conditions of considerable difficulty. Some other examples have escaped development about 1 km farther north, between Malakole Road and the beach berm (Figure 7). They are largely filled with rubble, but are the only easily inspected examples of Ewa Karst pit caves. They have no protection at all.

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Figure 7. Tidal pit cave near barge harbor. July 1997 photo by WRH.

Figure 8. Typical landscape in "8 Acre Tract." July 1997 photo by WRH

4) Present conservation efforts

No part of the Ewa Karst thus has been set aside as an example of the karst per se  but various individuals and organizations have achieved protection of small areas for coincidental reasons. A similar effort has long been spearheaded by Alan Ziegler, formerly a Bishop Museum vertebrate zoologist. The present protection of "B6-137" is largely due to his efforts, including 1990 testimony to the Hawaii State Legislature on behalf of the Hawaii Audubon Society (Ziegler, 1990 ash). "B6-22" already had been fenced as a result of his persuasiveness. For more than a decade he has been reasoning with the Campbell Estate, the Hawaii Department of Land and Natural Resources and legislature and anyone else he can persuade to listen and/or come and look at another 8-acre parcel confining more than 100 pit caves (Figures 8 and 9). The caves of this area also are notable for their content of bones of extinct birds and land snails (Figure 10). In 1990 he testified:

During the past several years, with the kind permission of the Campbell Estate, several hundred people including students of elementary school through university graduate level have enjoyed group visits to these conveniently located sinkholes and have even had an opportunity to climb down into one and dig for a few fossil bones themselves (Ziegler, 1990a).

But only in 1996 did a few members of Hawaiian internal organizations of the National Speleological Society learn of his work and see what he has shown so many others. We came away convinced. The proposed zoning change that would destroy this area still is in abeyance after more than a decade. But protection of the caves and the 8 acres of karst is an uphill struggle. It may seem amazing that, until recently, the world of cave conservation knew nothing of Ziegler's efforts. But perhaps it would have done nothing even if requested. very few cave conservationists are interested in working to save sinkholes when so many caves need protection so urgently. Truly, seeing is believing here, and understanding that these so-called sinkholes are karstic pit caves -- important structures in their own right, not just collapses containing bird bones and snails (Figure 10). One of these caves -- "Coralloid Cave" is a little chamber nearly 5 m deep, formed by the confluence of three chimneys (Figures 11 and 12). "Rusty Wire Sinkhole" also is better described as a pit cave, and there are more than 90 other ''sinkholes"/caves not yet seen by speleologists in this little 8-acre tract.

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Figure 9. Small phreatic dissolution-cavities in "8 Acre Tract''. July 1997 photo by WRH.

Figure 10. Subfossil bird bones and land snails from cave in "8 Acre Tract". March 1997 photo by WRH.

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Figure 11. Interior of Coralloid Cave. July 1997 photo by WRH.

Figure 12. Coralloid speleothems in Coralloid Cave. July 1997 photo by WRH.

5) Conclusions and recommendations

Obviously these little caves aren't much for recreational caving, and the area was dragged by bulldozers, but its scientific values are exceptional. Speleologists and karstographers should support Ziegler's effort.

Further, other small remnants of the original karstic features may remain farther east, protected only by chance. A detailed inventory of such remnants is badly needed. The planned closure of Barbers Point Naval Air Station offers a special window of opportunity. In any event, it is time to save some of the Ewa Karst for its own karstic values, as an example for all Hawaii.

Acknowledgments

Alan Ziegler provided notable on-site guide service and explanations of the resources and values of these small parts of the Ewa Karst, together with much background information. Chester Lao, Board of Water Supply hydrogeologist, provided information on the extent and hydrogeology of this karst, and Hunter Johnson and Michael Kliks of the Hawaii Grotto of the National Speleological Society provided logistic and field support.

References


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