Sundaland is the currently partially drowned continental landmass that encompasses Borneo, Sumatra, Java, and the Malay Peninsula. It has episodically been reclaimed by the sea during successive Quaternary glaciations, and is commonly thought to be vertically stable. Combining geomorphological observations with numerical simulations of coral reef growth and shallow seismic stratigraphy, we show that the Sunda shelf is subsiding, and that the intermittent regime of transgressions only prevailed over the past 400,000 yr. Prior to that time, Sundaland was permanently exposed. We relate these drowning events to transient dynamic topography in the Indo-Australian subduction zone. Because the Sunda shelf is very shallow, these new data provide important insights into Pleistocene paleogeography, with implications on the interactions between the solid Earth and climate, oceanography, and dispersal of species, including hominids.
Over the last decade, studies of natural hazards in Sumatra have focused primarily on great earthquakes and associated tsunamis produced by rupture of the Sunda megathrust. However, the Sumatran Fault and the active volcanic arc present proximal hazards to populations on mainland Sumatra. At present, there is little reliable information on the maximum magnitudes and recurrence intervals of Sumatran Fault earthquakes, or the frequency of paroxysmal caldera-forming (VEI 7-8) eruptions. Here, we present new radiocarbon dates of paleosols buried under the voluminous Ranau Tuff that constrain the large caldera-forming eruption to around 33,830-33,450 calender year BP (95% probability). We use the lateral displacement of river channels incised into the Ranau Tuff to constrain the long-term slip rate of two segments of the Sumatran Fault. South of Ranau Lake, the Kumering segment preserves isochronous right-lateral channel offsets of approximately 350 ± 50 m, yielding a minimum slip rate of 10.4 ± 1.5 mm/year for the primary active fault trace. South of Suoh pull-apart depression, the West Semangko segment offsets the Semangko River by 230 ± 60 m, yielding an inferred slip rate of 6.8 ± 1.8 mm/year. Compared with previous studies, these results indicate more recent high-volume volcanism in South Sumatra and increased seismic potency of the southernmost segments of the Sumatran Fault Zone.
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