LITTORAL HYDROVOLCANIC EXPLOSIONS - A CASE-STUDY OF LAVA-SEAWATER INTERACTION AT KILAUEA VOLCANO

A variety of hydrovolcanic explosions may occur as basaltic lava flows into the ocean. Observations and measurements were made during a two- year span of unusually explosive littoral activity as tube-fed pahoeho e from Kilauea Volcano inundated the southeast coastline of the island of Hawai'i. Our observations suggest that explosive interactions requ ire high entrance fluxes (greater than or equal to 4 m(3)/s) and are m ost often initiated by collapse of a developing lava delta. Two types of interactions were observed. ''Open mixing'' of lava and seawater oc curred when delta collapse exposed the mouth of a severed lava tube or incandescent fault scarp to wave action. The ensuing explosions produ ced unconsolidated deposits of glassy lava fragments or lithic debris. Interactions under ''confined mixing'' conditions occurred when a lav a tube situated at or below sea level fractured. Explosions ruptured t he roof of the tube and produced circular mounds of welded spatter. We estimate a water/rock mass ratio of 0.15 for the most common type of littoral explosion and a kinetic energy release of 0.07-1.3 kJ/kg for the range of events witnessed.