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Giant phreatic eruptions at Milos Island (Greece)

Roverato M. 1, Lucchi F.1, Massaro S.2,3, Natale J.2, , Sulpizio R.2, Tranne C.A.1, Ventruti G.2, Vougioukalakis G.4

  • Affiliations: (1) Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Bologna (Italy) (2) Dipartimento di Scienze della Terra e Geoambientali, Università di Bari (Italy) (3) Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna (Italy) (4) Hellenic survey of Geology and Mineral Exploration 

  • Presentation type: Poster

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

  • Poster Board Number: 71

  • Programme No: 3.14.5

  • Theme 3 > Session 14

Abstract

Phreatic eruptions rank amongst the most dangerous and enigmatic volcanic phenomena on Earth. These events are typically associated with the rapid vaporization of hydrothermal waters within geothermal systems due to hot fluids and heat from, among others, magma intrusions, suddenly converting thermal energy into mechanical work. Hydrothermal system host-rock fragmentation and the subsequent ejection of particles allow for the accumulation of deposits with no fresh juvenile material involved. Milos Island (Greece), located in the central part of the Hellenic Volcanic Arc, hosts extensive geothermal systems in its southeastern part, where favourable conditions for phreatic explosions occur. The island underwent several phases of phreatic activity during the Pleistocene. Our preliminary results have revealed that at least two exceptional gigantic phreatic eruptions of unknown age (100ka<>1Ma) occurred within the Mesozoic/Palaeogene metamorphic basement. This activity emplaced several eruptive units up to 50 m thick, consisting of extremely poorly sorted deposits of clast-supported angular lithic lapilli and blocks (up to 1 m in size), mainly formed by schists. We primarily interpreted the eruptive units as extensive pyroclastic density currents with subordinate very proximal fallout deposits, which overall, cover a minimum area of 15km² (on land) with a maximum runout of 7 km from the inferred source. We believe that this represents one of, if not the greatest, phreatic events known worldwide. Further analysis is needed to better understand the main factors controlling the preparatory state of both fluids and the host reservoir, as well as the priming mechanisms leading to such large-scale eruptive events.