FY 2003

Observations and sampling of an ongoing subsurface eruption of Kavachi volcano, Solomon Islands, May 2000

Baker, E.T., G.J. Massoth, C.E.J. de Ronde, J.E. Lupton, and B.I.A. McInnes

Geology, 30(11), 975–978 (2002)

A serendipitous encounter with an erupting, shallow submarine volcano in the Solomon Islands provided a rare opportunity to map and sample the dispersal of volcanogenic emissions into the surrounding water column. Kavachi, episodically active since at least 1939, is a forearc volcano located on the Pacific plate only ~30 km northeast of its convergent boundary with the downgoing Indo-Australian plate. During 14 May 2000 we observed explosive phreatomagmatic eruptions at several minute intervals, creating a complex distribution of plumes of volcanic glass shards throughout the water column at a distance of ~1.5 km from the summit. At distances of 4-5 km, shallow-water (<250 m) plumes had dissipated, but deeper plumes were ubiquitous down to seafloor depths of 1500 m. Only 2 of 22 water samples (at 14 and 237 m depth) showed evidence of hydrothermal and magmatic enrichment. These samples were elevated in δ³He, Fe, and Mn (one sample only), but not in CO₂. We infer that the volcano flanks were essentially impermeable to fluid emissions and that the observed particle halo was created by magma shattering and resuspension. Most magmatic and hydrothermal fluids were thus discharged directly from the summit into the atmosphere.