Timing, Rates and History of Post-YTT (<74ka) Resurgent Uplift of Samosir Island, Toba, Sumatra

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Large calderas like Toba, Sumatra are the sites of the most devastating natural events on Earth, supereruptions. With their potential to cause regional devastation and global disaster, understanding the processes and timescales of these supervolcanoes is crucial to being able to address potential hazards. While the climactic eruptions are the main event, these are just instances that punctuate long periods of relative calm. It is during these "resurgent" periods that supervolcanoes recover and readjust before the next eruption cycle. Critical information about the pre- and post-climactic activity of a supervolcano is encoded during this period, yet despite decades of research, resurgence remains poorly understood. This is of concern because most hazardous calderas today are in a resurgent stage. The goal of this project is to understand the timescale, rates, duration, and mechanisms that occur at large resurgent calderas through a case study of the Toba caldera, Sumatra, the Earth's most recent supervolcano.Since the climactic eruption of 2500 km^3 of magma 74 ka as the Young Toba Tuff (YTT), there is evidence of several small eruptions within the Toba caldera as well over 1 km of vertical uplift of the caldera floor to form the island of Samosir. The hypothesis that remnant magma left after the climactic eruption was the source of this resurgence will be addressed through a program of stratigraphic correlation and age dating to reveal the spatiotemporal pattern of eruptions and the rate and motivating force for the uplift. Post YTT lavas are to be dated using coupled U-series and (U/Th)/He age determinations in zircon to resolve eruption ages and the rate and duration of uplift of Samosir are to be investigated using a combination of C-14 age dating and time control through stratigraphic correlation using paleomagnetic properties of uplifted lake sediments on Samosir. Toba's relative youth is a unique advantage among large calderas and it is anticipated that this project will reveal unprecedented details of the post-climatic history and longevity of a large caldera and its magmatic system that can be used to inform more sophisticated numerical models of caldera mechanics than currently available. Furthermore, the serendipitous opportunity to address previously recalcitrant aspects of the region's geomagnetic field will attract further attention to Toba and this work. Graduate students will receive interdisciplinary training in modern caldera science and associated geochronology within an international collaborative framework with colleagues in USA, Germany, Australia, and Indonesia. The science conducted will give further impetus to efforts to develop a UNESCO Geopark at Toba.