Subaqueous Pyroclastic Flows from Krakatau and Tambora Volcanoes, Indonesia

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The historic explosive eruptions of Krakatau (1883) and tambora(1815) volcanoes in Indonesia discharged over 40 km 3 of pyroclastic material into the sea, mostly as voluminous gravity flows. With previous funding samples have been obtained of the submarine deposits areound Krakatau volcano by a diver.deployed coring system. The study focussed on the origin of two ephmeral islands, Steers and Calmeyer, that formed to the nortwest of Krakatau as a result of the catastrophic 1883 eruption. Underwater geologic mapping and preliminary examination of sediment cores indicate that the two islands were formed by the entrance of subaerially.generated pyroclastic flows into the sea. The findings have shed new light on the controversy surrounding the origing of devstating tsunamis associated with the eruption and the fate of Krakatau island during the paroxymal stage of the event. New funds for as additional will be used to carry outstudies on the samples collected in 1990 and existing samples of the tambora 1815 deposits. Thermal demagnetization studies on pumice and lithic clasts from the subaqueous pyroclastic flow deposits will be made to determine emplacement temperatures and investigate the role of seawater as colling agent during subaqueous transport and deposition. Detailed grain size, component abundance, and image analysis will also be carried out to evaluate the nature of hot, pyroclastic flow interactions with seawater. These result will be significant in terms of understanding the eruptive processes of these event sand providing modern analogues of volcaniclastic sedimentation that can be applied to ancient convergent margin sequences in the geologic record.