LAVA-SEAWATER INTERACTIONS AT SHALLOW-WATER SUBMARINE LAVA FLOWS

Hydrothermal plumes associated with nearshore lava flows from Kilauea Volcano, Hawaii were studied on five occasions during 1989-1990 to address the current lack of data on direct lava-seawater interactions. The following enrichments were found in the sea-surface hydrothermal plumes above the active underwater lava flows: H2, 15,000x ambient seawater concentrations; Mn, 250x; and Si, 20x. Water temperatures reached 46-degrees-C. Lower concentrations and temperatures were observed in the plumes with increasing distance from shore, with H-2, Si, and Mn concentrations linearly related to seawater temperature. Unlike deep sea spreading center hydrothermal plumes, no CH4 enrichment was observed. The elevated H-2 is likely to be from water-rock reactions, rather than from the release of magmatic gas. The plume mass/heat ratios presented here suggest that submarine flood basalts, although aerially large, should be relatively small immediate contributors to oceanic geochemical cycles compared to hydrothermal circulation through the crust.