A geological record of highly explosive eruptions from Sumatra (Indonesia)

Explosive volcanism on the island of Sumatra (Indonesia) has produced infrequent, yet destructive calderaforming eruptions such as those from the well-known Toba caldera. Although the Toba ignimbrites have been studied extensively, pyroclastic deposits from other highly explosive eruptions in the region have received much less attention. Here, we present a comprehensive characterization of proximal pyroclastic deposits associated with highly explosive eruptions across the western Sunda volcanic arc. We use a multifaceted approach that integrates literature with original proximal stratigraphic data, along with detailed geochemical and geochronological investigations. Although the compositions of the studied pyroclastic deposits are predominantly rhyolitic and estimates of intensive parameters indicate similar pre-eruptive storage conditions across the different sectors of the Sumatran arc, their characteristic geochemical signatures, combined with mineral assemblages, allow for the distinctive fingerprinting of the individual volcanic sources. Our geochronological data reveal that between ~ 7.3 Ma and 33 ka, the Sumatran region experienced multiple highly explosive eruptions (VEI ≥ 6) often associated with caldera collapses, as well as moderately explosive eruptions (VEI ≤ 5) from stratovolcanoes. The apparent frequency of highly explosive eruptions increased gradually during the Quaternary and peaked in the last 48 ky. These findings substantially redefine the regional frequency of highly explosive eruptions from Sumatra. Additionally, given that most information regarding explosive Sumatran eruptions are derived from deep-sea tephra layers with unknown sources, our results provide a strong underpinning for robust tephra correlations along the western Sunda volcanic arc and the wider Southeast Asia region.