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Far-travelled ash megaturbidite fed by shoreline-crossing pyroclastic currents from the Kos Plateau Tuff eruption. IODP Expedition 398, Hellenic Arc Volcanic Field

Tim Druitt 1, Abigail Metcalfe1, Katharina Pank2, Steffen Kutterolf2, Jonas Preine3, Karim Kelfoun1, Christian Hübscher4, Paraskevi Nomikou5, Thomas Ronge6, and IODP Expedition 398 scientists.

  • Affiliations:  1University Clermont-Auvergne, Laboratoire Magmas et Volcans, Clermont-Ferrand, France; 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany; 3Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole MA, USA; 4Institute of Geophysics, University of Hamburg, Hamburg, Germany; 5Department of Geology and Geoenvironment, National and Kapodistrian University of Athens, Athens, Greece; 6International Ocean Discovery Program, Texas A&M University, College Station TX, USA. 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 79

  • Programme No: 6.2.15

  • Theme 6 > Session 2

Abstract

Explosive eruptions from island volcanoes deliver huge quantities of ash to the marine environment. While many of the transport pathways are understood, those from shoreline-crossing or submarine pyroclastic currents, and the water-supported gravity flows into which they transform, are not. We report the discovery during IODP Expedition 398, of an ash megaturbidite up to 200 m thick buried deep in the rift basins of the South Aegean Volcanic Arc. The 80 cubic km of ash derives from the 161 thousand-year-old Kos Plateau Tuff (KPT) caldera-forming eruption 120 km to the east, as shown by offshore-onshore chemical correlation of glasses and minerals. The marine ash forms a chemically homogeneous graded bed that lacks internal bioturbation. This implies an emplacement time of less than the several months to years typically required for seabed re-population by burrowing organisms. We propose that the ash bed sedimented from a stream of eruption-fed turbidity currents that travelled westwards 120 km from the Kos eruptive center down arc-parallel slopes to the rift basins. These basins at the time were deep bathymetric troughs that captured the Kos-derived turbidity currents, allowing great thicknesses of ash to accumulate far from the eruption source. The megaturbidite increases the total erupted volume of the KPT eruption to >200 cubic km (uncompacted), suggesting that eruption volumes for other island or coastal explosive eruptions may also be underestimated. The study highlights how large volcanic eruptions re-mould sea floor landscapes, lay down ash megabeds, and destroy seafloor biota on island-arc-wide scales in short-lived, catastrophic events.