Rapid Cooling of Volcano Nislhinoshima-shinto, the Ogasawara Islands (Part1) : Observational Results

Abstract

Various geothermal measurements were conducted during and after the eruptive activity of a new volcano Nishinoshima-shinto, the Ogasawara Islands. Ground temperature at 1Ocm depth was 580℃ at four months and 178℃ at seventeen months after the eruptive activity. Maximum surface temperature was 90゜～100℃ at thirteen months and 54゜～66℃ at seventeen months after the eruptive activity. Heat discharge decreased from 2.7x10⁷ cal/sec at the eruptive stage (Sekioka and Yuhara, 1976) to 3.3×10⁶ cal/sec at seventeen months after the eruptive activity. Thus, all the thermal data show rapid cooling of the Nishinoshima-shinto. The reason of the rapid cooling may be explained by two manners. 0ne is that the heat source (solid magmatic body) in the ground after the eruptive activity is very small. Another is that the sea water affects essentially on the cooling of the heat source. Such rapid cooling may be one of the typical features of submarine volcanic activities.