Pre-eruptive conditions and triggering mechanism of the ~ 16 ka Santa Bárbara explosive eruption of Sete Cidades Volcano (São Miguel, Azores)

  • Kathrin Laeger
  • Maurizio PetrelliEmail author
  • Daniele Morgavi
  • Michele Lustrino
  • Adriano Pimentel
  • Joali Paredes-Mariño
  • Rebecca L. Astbury
  • Ulrich Kueppers
  • Massimiliano Porreca
  • Diego Perugini
Original Paper


The Santa Bárbara trachytic eruption (~ 16 ka) was one of the major eruptions of the Sete Cidades Volcano (São Miguel Island, Azores), recording the last phase of caldera formation. Here, we report and combine geochemical, mineralogical, and petrological constraints on natural samples with time-series experiments to describe the pre-eruptive conditions of the Santa Bárbara plumbing system. The trachytic pumice clasts are notably characterized by the presence of hawaiitic enclaves, banded textures (~ 60–67 wt% SiO2) and high variability in mineral phases, occasionally rounded and partially resorbed. The hawaiitic enclaves contain quench textures such as sharp contacts with the trachytic groundmass, as well as acicular and skeletal growth of several minerals, pointing to a high-temperature gradient between the hot hawaiitic magma and the colder trachytic reservoir. Distinct phenocryst rim compositions in both magmas exclude significant chemical diffusion. We suggest that the hawaiitic enclaves represent an intrusion that triggered the eruption, but was only partially involved in the mixing process that generated the banded groundmass textures. These textural heterogeneities are interpreted to be related to a self-mixing event induced by convection within a compositionally zoned reservoir, with trachytic and mugearitic magmas at the top and the bottom, respectively. In detail, the model requires the likely arrival of hawaiitic magma to the base of the reservoir, inducing mixing by reheating of the resident mugearitic magma and volatile transfer. These processes produced a thermo-chemical destabilization (i.e., convection) of the shallow reservoir and mixing between the mugearitic and the trachytic magmas. We reproduced the observed chemical signatures performing time-series mixing experiments and calculated the concentration variance decay during mixing. Estimated timescales indicate that the hawaiitic intrusion took place ~ 41 h before the onset of the eruption.


Azores Fractional crystallization Homogenization Mafic enclaves Magma mixing Time-series experiments 



This study has been funded under the European Union’s Seventh Framework Programme FP7 “FP7-People-2013-ITN”, grant agreement number 607905 (VERTIGO). DM and MP acknowledge the University of Perugia (Progetti Ricerca di base MORGABASE 2015 and CHALLENGE) for financial support. ML acknowledges Sapienza Università di Roma (Progetti Ricerca Ateneo 2015, 2016 and 2017) for financial support. UK acknowledges financial support during field work from Project M1.1.2/I/009/2005/A of the Portuguese foundation Fundação Gaspar Frutuoso. DP acknowledges the European Research Council with the Consolidator grant CHRONOS (612776) and PRIN n. 2010TT22SC 004. We gratefully acknowledge the help of H. Lohringer, D. Müller (both LMU), M. Serracino and M. Albano (CNR, Rome) and D. González-García (Perugia) for the help during sample preparation and chemical analyses. The authors acknowledge Mickael Laumonier and an anonymous reviewer for the constructive comments that allowed improving the manuscript significantly.

Supplementary material

410_2019_1545_MOESM1_ESM.xlsx (133 kb)
Supplementary material 1 (XLSX 132 KB)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Kathrin Laeger
    • 1
  • Maurizio Petrelli
    • 1
    Email author
  • Daniele Morgavi
    • 1
  • Michele Lustrino
    • 2
    • 3
  • Adriano Pimentel
    • 4
    • 5
  • Joali Paredes-Mariño
    • 1
  • Rebecca L. Astbury
    • 1
  • Ulrich Kueppers
    • 6
  • Massimiliano Porreca
    • 1
  • Diego Perugini
    • 1
  1. 1.Department of Physics and GeologyUniversity of PerugiaPerugiaItaly
  2. 2.Dipartimento di Scienze della TerraSapienza Università di RomaRomeItaly
  3. 3.Istituto di Geologia Ambientale e Geoingegneria, CNRRomeItaly
  4. 4.Instituto de Investigação em Vulcanologia e Avaliação de Riscos (IVAR)Universidade dos AçoresPonta DelgadaPortugal
  5. 5.Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA)Ponta DelgadaPortugal
  6. 6.Department of Earth and Environmental SciencesLudwig-Maximilians-Universität (LMU) MunichMunichGermany

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