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Front. Earth Sci. | doi: 10.3389/feart.2019.00122

Biased Volcanic Hazard Assessment due to Incomplete Eruption Records on Ocean Islands: An Example of Sete Cidades Volcano, Azores

  • 1Department of Geological and Environmental Sciences, Ludwig Maximilian University of Munich, Germany
  • 2Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA), Portugal
  • 3Instituto de Investigação em Vulcanologia e Avaliação de Riscos (IVAR), Portugal
  • 4ETH Zürich, Switzerland
  • 5Dipartimento di Fisica e Geologia, Università di Perugia, Italy

Sete Cidades is the westernmost central volcano of São Miguel Island, Azores. Although currently dormant, it has been the most active volcano on the island in the past 5 ky, with at least 17 trachytic intra-caldera explosive eruptions, some of which of sub-Plinian. The last paroxysmal explosive eruption took place ~16 ka, enlarging the summit caldera to its present dimensions, and is recorded by the Santa Bárbara Formation. It is well known that explosive eruptions pose serious hazards to local communities and may have worldwide impacts. However, the products of explosive eruptions on volcanic islands are almost inevitably incompletely preserved, thereby impeding our ability to precisely determine eruptive source parameters. These constraints are frequently observed on volcanic ocean islands, such as the Azores islands, where it is estimated that a significant portion of the erupted material is deposited into the sea. We here present evidence of a distal deposit (>25 km from the vent) that can be correlated with the pumice fall deposit of the Santa Bárbara Formation based on deposit characteristics, textural features and geochemistry. This is the first evidence of a decimeter-thick distal deposit of Sete Cidades volcano in the central part of São Miguel Island, which allows to constrain eruptive source parameters and wind conditions. The predominant winds blowing from westerly directions makes Sete Cidades the most hazardous volcano for the entire island of São Miguel with its current population of >137,000 inhabitants. Most critically, the main harbor, only airport and hospital are located in the capital city of Ponta Delgada, ~12 km SE from Sete Cidades caldera. In case of a future explosive eruption, under westerly-blowing wind conditions, the impact on São Miguel will be catastrophic, with long-term economic consequences.

Keywords: Ocean island volcano, incomplete eruption record, Explosive eruption, Eruptive scenarios, São Miguel Island, Tephra fallout, inverse problem, volcanic hazard

Received: 20 Nov 2018; Accepted: 07 May 2019.

Edited by:

Roberto Sulpizio, University of Bari Aldo Moro, Italy

Reviewed by:

Dario Pedrazzi, Instituto de Ciencias de la Tierra Jaume Almera (ICTJA), Spain
Federico Lucchi, University of Bologna, Italy  

Copyright: © 2019 Kueppers, Pimentel, Ellis, Forni, Neukampf, Pacheco, Perugini and Queiroz. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Ulrich Kueppers, Department of Geological and Environmental Sciences, Ludwig Maximilian University of Munich, Munich, Germany,