Stress Triggering of the 2005 Eruption of Sierra Negra Volcano, Galápagos

Extensive vertical deformation (>4.5 m) observed at Sierra Negra volcano Galápagos, Ecuador, between 1992 and the 2005 eruption led scientists to hypothesize that repeated faulting events relieved magma chamber overpressure and prevented eruption. To better understand the catalyst of the 2005 eruption, thermomechanical models are used to track the stress state and stability of the magma storage system during the 1992–2005 inflation events. Numerical experiments indicate that the host rock surrounding the Sierra Negra reservoir remained in compression with minimal changes in overpressure (~10 MPa) leading up to the 2005 eruption. The lack of tensile failure and minimal overpressure accumulation likely inhibited dike initiation and accommodated the significant inflation without the need for pressure relief through shallow trapdoor faulting events. The models indicate that static stress transfer due to the Mw 5.4 earthquake 3 hr prior to the eruption most likely triggered tensile failure and catalyzed the 2005 eruption. Plain Language Summary Tracking the stability of a magma system in the lead up to a volcanic eruption requires investigating both the pressure state of the magma reservoir and stress accumulation in the host rock. New coupled conduit flow‐magma reservoir pressurization models are used to evaluate the evolution of the magma reservoir of Sierra Negra volcano, Galápagos, in the lead up to its 2005 eruption. Stress calculations indicate that the magma reservoir was stable prior to the 2005 eruption and that the eruption was likely triggered by a Mw 5.4 earthquake that occurred 3 hours prior to the event. The new modeling approach has important implications for tracking the stress evolution of magma systems to evaluate future unrest and eruption triggering mechanisms at volcanoes worldwide. Key Points New thermomechanical models provide an estimation of magma system stability in the lead up to the 2005 eruption of Sierra Negra Models suggest that Sierra Negra's magma system was in stable storage prior to eruption with minimal overpressure and no tensile failure Coulomb static stress calculations indicate that a Mw 5.4 earthquake likely triggered the 2005 eruption