Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 65 Number 1: 53-67 April 2003

A publication of the National Speleological Society

The Kukaiau Cave, Mauna Kea, Hawaii, Created by Water Erosion, a New Hawaiian Cave Type
Stephan Kempe and Marlin Spike Werner

Abstract

In 2000 and 2001, two large (each ca. 1000 m long) cave systems have been surveyed on the eastern, heavily eroded, flank of Mauna Kea: The Pa’auhau Civil Defense Cave and the Kuka‘iau Cave (at first called ThatCave/ThisCave System). Both caves occur in the Hamakua Volcanics, 200-250 to 65-70 ka old. They are the first substantial caves documented for lavas of Mauna Kea and the first caves on Hawaii showing extensive morphological signs of water erosion.

The Pa’auhau Civil Defense Cave is a lava tube, as attested by the presence of the typical morphological elements of lava tubes, including secondary ceilings, linings, base sheets, stalactites and lava falls. Subsequently, the cave was modified erosionally by a stream which entered upslope and traversed much, but not all, of the cave, leaving waterfalls, waterfall ponds, scallops, gravel, rounded blocks and mud (Kempe et al. 2003). In contrast the Kuka‘iau Cave – a still active stream cave with a vadose and phreatic section - is essentially erosional in origin. This is concluded from the geology of the strata exposed in the cave and from its morphology: At the upper entrance the cave is situated in a thick series of aa and the lower section was created by removing aa and diamict layers, therefore excluding the possibility that the cave developed from a precursor lava tube. Also, in its phreatic section, the cave makes several right angle turns and moves upward through a series of pahoehoe sheets, unlike any lava tube. Furthermore, a base layer can be followed along which the major section of the upper cave has developed. Allophane and halloysite – minerals produced by weathering - helped in sealing the primary porosity of this base layer causing a locally perched water table. Water moving along this base layer on a steep hydraulic gradient through the interstices of aa and through small pahoehoe tubes exerted a high pressure on the porous diamict of the lower cave, causing its erosional removal. Our observations of water erosional caves in lavas of Hawaii offer a new perspective on deep-seated water courses in volcanic edifices.

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