Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 65 Number 1: 76-85 April 2003

A publication of the National Speleological Society

Pa'auhau Civil Defense Cave on Mauna Kea, Hawaii - A Lava Tube Modified by Water Erosion
Stephan Kempe, Ingo Bauer, and Horst-Volker Henschel

Abstract

In 2000 and 2001, 2 large (1000 m long) cave systems were surveyed on the eastern, heavily eroded flank of Mauna Kea: The Pa‘auhau Civil Defense Cave and the Kuka‘iau Cave. Both caves occur in the Hamakua Volcanics, 200-250 to 65-70 ka old. They are the first substantial caves documented for lavas of this volcano and the first caves on the island of Hawaii showing extensive morphological signs of water erosion.

All observations lead to the conclusion that the Kuka‘iau Cave is erosional in origin (Kempe & Werner 2003). These observations include: missing lava tube features, a graded hydraulic profile, a base layer along which the major section of the cave seems to have developed, and allophane and halloysite that sealed the primary porosity causing a locally perched water table.

In contrast to this feature, the Pa‘auhau Civil Defense Cave originated as a lava tube. This is attested to by the presence of the typical morphologic elements of a lava tube, such as secondary ceilings, linings, base sheets, lava stalactites, and lava falls. Nevertheless, the cave was heavily modified by a stream that entered upslope and traversed much, but not all, of the cave. It left waterfall walls, large plunge pools, stream potholes, scallops, flutes, gravel, rounded blocks, and mud.

The finding of water-erosional caves in the lavas of Hawaii offers a new view on deep-seated water courses in volcanic edifices.

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