CALDERA ACTIVITIES IN NORTH BALI, INDONESIA

Abstract

One of the most serious natural hazards is largescaled Plinian eruption that forms caldera. Although the probability to have such large-scaled eruption is very low, the result will be catastrophic if it happens. Thus, it is important to clarify features of caldera system including eruption timing, scale of eruption, precursor activity, etc. With enough scientific information, we may be able to mitigate such very rare but extremely large-scaled geohazard. In Bali Island, Indonesia, there are two caldera systems; Batur caldera and Buyan-Bratan caldera. Batur caldera was previously well studied (e.g. Sutawijaya, 2009), whilst Buyan-Bratan caldera’s geological and volcanological features have not been examined at all. The Buyan-Bratan caldera is about 6 km × 11 km in size and contains three caldera lakes. Wellformed several post-caldera cones are covered by thick soil and vegetation and developed from central to southern part of the caldera. BuyanBratan caldera and post-caldera cones are thought to be older than Batur caldera activities. Geothermal manifestation is confirmed within the caldera. Geological features of the Buyan-Bratan caldera and post-caldera cones were clarified by petrographic and petrochemical analyses. Also, KAr ages were obtained for each volcanic edifice in Buyan-Bratan caldera system.

Keywords: Caldera, Plinian eruption, Buyan, Batur, volcano hazards