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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.