LAVA TUBES AS GROUNDWATER CONDUITS

The role of lava tubes in groundwater conduits has barely been mentioned in recent geological literature. Lava tube conduits differ significantly from karstic conduits because they commonly are surrounded by permeable lava and/or other material in which the piezometric surface rises and falls precipitously. Within such media, lava tubes function as leaky pipes. Elsewhere, however, lava tubes are floored by or underlain by dense, impermeable basalt or by volcanic ash which hydrolizes to clay. In such locations, lava tube caves have been observed to carry high-velocity flow for significant distances.

This process is of special importance on Hawaii Island, Hawaii. No groundwater tracer studies are on record on this large island even though human and animal wastes and other toxic and hazardous materials traditionally have been dumped in skylights and entrances of lava tube caves. To date, no human impact from this problem is documented, but with increasing urbanization of large pseudokarstic areas, it can no longer be ignored. Also in question is a possible role of tube-transmitted pesticides and herbicides in the recent decimation of the island's marine fisheries.