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Pre- & Syn-Eruptive Deformation and Seismicity at a Basaltic Caldera: Cascading Processes Leading to Eruption During the 2018 Eruption of Sierra Negra, Galapagos

Peter C. LaFemina 1,2, Andrew F. Bell3, Patricia M. Gregg4, Zilin Song5, Lillian Lucas4, Mario Ruiz6, Stephen Hernandez6, Yen Joe Tan5, Sofie Butcher3, Matthew Head4

  • Affiliations: 1Alfred Wegener Institute, Helmholtz Center for Polar & Marine Research, Bremerhaven, Germany; 2Department of Geosciences, Universitat Bremen, Bremen, Germany; 3School of Geosciences, University of Edinburgh, Edinburgh, UK; 4Department of Earth Science & Environmental Change, University of Illinois Urbana-Champaign, Urbana, IL, USA; 5Department of Earth and Environmental Sciences, The Chinese University of Hong Kong, Hong Kong S.A.R., China; 6Instituto GeofĂ­sico, Escuela PolitĂ©cnica Nacional, Quito, Ecuador

  • Presentation type: Poster

  • Presentation time: Friday 16:30 - 18:00, Room Poster Hall

  • Poster Board Number: 47

  • Programme No: 2.3.33

  • Theme 2 > Session 3

Abstract

The June 26 2018 eruption of Sierra Negra volcano, Galapagos Islands provides an opportunity to investigate volcano-tectonic interactions and magmatic processes in a basaltic caldera, including eruption triggering and caldera resurgence. Geodetic and seismic observations for the eruption cycle (2005 to 2018) provide new observations of dynamic caldera processes including: 1) the largest historically recorded pre-eruptive inflation (>6.5 m) and co-eruptive deflation (~8.5 m) without displacements on the ring fault; 2) correlation of uplift (inflation) and subsidence (deflation) rates with intra-caldera seismicity rates; 3) a reversal in slip polarity on the intra-caldera Trapdoor Fault system (TDF) from uplift during pre-eruptive to subsidence during co-eruptive events; 4) co-seismic displacements of >1.8 m due to a Mw5.4 earthquake on the TDF ~8 hours before eruption; and 5) net uplift (resurgence) of ~2.0 m of the Sinuous Ridge along the TDF. Here, we focus on geodetic and seismic observation of the ~9 hour period between the Mw5.4 TDF earthquake and eruption initiation. Repeating long period (LP) seismicity started ~3 hours and magma migration ~8 hours after the earthquake. The repeating LP earthquakes indicate failure and/or fluid processes along fault and fracture systems in regions of positive Coulomb Failure Stress change. Vertical and horizontal displacement of 2 cGNSS stations ~8 hours after the earthquake are best-fit by contemporaneous passage of a near vertical intrusion from a 2 km deep sill to eruptive fissures and deflation of the sill. These observations suggest a series of cascading process related to stress changes on the TDF.