Mastin, L.G., and Witter, J.B., 1996, A New Database on Eruptions ThroughLakes and Shallow Water Bodies, in "Crater Lakes, Terrestrial Degassingand Hyper-acid Fluids in the Environment," Proceedings of a ChapmanConference at Crater Lake, Oregon, September 4-9, 1996, J. Varekamp and G.L. Rowe, convenors, p. 34.
Hundreds of volcanoes worldwide contain caldera or crater lakes, or liebelow shallow seawater. The potential for violent mixing of water withmagma presents a special hazard at these volcanoes, yet the degree ofhazard is difficult to evaluate. Mixing of water with magma has clearlymade some eruptions (e.g. Surtsey, 1964; Taal, 1965) more explosive thanthey otherwise would have been. Yet during other eruptions (e.g. currentinflux of lava into the sea at Kilauea, Hawaii), magma and surface water mix relatively non-violently.The factors that affect the violence ofmixing presumably include magma type, mass eruption rate, degree ofinitial magma fragmentation, and water depth, among other things. Somethermodynamic and eruptive models (e.g. Wohletz, 1986, Bull. Volc.,48:245-264; Koyaguchi & Woods, 1996, JGR, 101:5561-5574) have attempted toidentify conditions (mainly water/magma ratios) under which mixing is mostviolent. However no study has yet attempted to systematically relate theviolence of observed eruptions with known hydrologic and magmatic conditions. We are compiling a worldwide data base of eruptions throughshallow water to address this question. At this early stage of study,more than 100 eruptions have been catalogued from more than 30 volcanoes.The magma type, eruption rate, erupted volume, water depth, and verbaldescriptions of eruptive phenomena, where available, have all beenincorporated. Some preliminary observations are that: (1) the mostviolent mixing seems to occur during moderate rates of magma injection(e.g. Taal, 1965). (2) During very high magma injection rates (e.g.Krakatau, 1883) water/magma ratios are frequently (though not always) toolow to significantly affect explosivity, while for low flux rates, (e.g.dome growth, subaqueous lava flows), magma does not intimately mix withwater. (3) hydromagmatic eruptions that breach the surface generally risefrom water depths of tens of meters or less. However a few have beenrecorded from depths of hundreds of meters. High gas content, or highmass flux, may affect the ability of magma to erupt through deep water.
Submitted by Larry G. Mastin.
An online version of the database described in this article is inprogress. For more information contact:
L G Mastin
- U.S. Geological Survey, 5400 MacArthur Blvd.,
Vancouver, WA 98661; 360-696-7518;
- Dept. of Geology & Geophysics, Univ. of Hawaii, 2525 Correa Rd.,
Honolulu, HI 96822; 808-956-2561;