Abstract
Caldera-forming eruptions of island volcanoes generate tsunamis by the interaction of different eruptive phenomena with the sea. Such tsunamis are a major hazard, but forward models of their impacts are limited by poor understanding of source mechanisms. The caldera-forming eruption of Santorini in the Late Bronze Age is known to have been tsunamigenic, and caldera collapse has been proposed as a mechanism. Here, we present bathymetric and seismic evidence showing that the caldera was not open to the sea during the main phase of the eruption, but was flooded once the eruption had finished. Inflow of water and associated landsliding cut a deep, 2.0–2.5 km3, submarine channel, thus filling the caldera in less than a couple of days. If, as at most such volcanoes, caldera collapse occurred syn-eruptively, then it cannot have generated tsunamis. Entry of pyroclastic flows into the sea, combined with slumping of submarine pyroclastic accumulations, were the main mechanisms of tsunami production.
Highlights
Caldera-forming eruptions of island volcanoes generate tsunamis by the interaction of different eruptive phenomena with the sea
Our new constraints on the mechanisms of tsunami generation associated with the Late Bronze Age (LBA) eruption arise from a multi-beam bathymetric study, supplemented by seismic profiling, of the three straits connecting the caldera to the sea
This rules out caldera collapse as a major mechanism of tsunami generation associated with the LBA eruption
Summary
Caldera-forming eruptions of island volcanoes generate tsunamis by the interaction of different eruptive phenomena with the sea. Recent seismic reflection profile studies have revealed three main stratigraphic units within the upper B200 m of the intracaldera fill, numbered 1 to 3 from the top-down[10]: flat-lying sediments from modern mass wasting of the caldera cliffs (unit 1), volcaniclastic sediments produced during the early submarine stages of Kameni Volcano (unit 2), and downfaulted material interpreted as the top of the LBA eruption products (unit 3). Other subdivisions of these same layers have been published[11]. We show by modelling that the main phase of caldera flooding cannot have taken more than 2 days to arrive at completion
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