Caldera resurgence during the 2018 eruption of Sierra Negra volcano, Galápagos Islands

Abstract

Recent large basaltic eruptions began after only minor surface uplift and seismicity, and resulted in caldera subsidence. In contrast, some eruptions at Galápagos Island volcanoes are preceded by prolonged, large amplitude uplift and elevated seismicity. These systems also display long-term intra-caldera uplift, or resurgence. However, a scarcity of observations has obscured the mechanisms underpinning such behaviour. Here we combine a unique multiparametric dataset to show how the 2018 eruption of Sierra Negra contributed to caldera resurgence. Magma supply to a shallow reservoir drove 6.5 m of pre-eruptive uplift and seismicity over thirteen years, including an Mw5.4 earthquake that triggered the eruption. Although co-eruptive magma withdrawal resulted in 8.5 m of subsidence, net uplift of the inner-caldera on a trapdoor fault resulted in 1.5 m of permanent resurgence. These observations reveal the importance of intra-caldera faulting in affecting resurgence, and the mechanisms of eruption in the absence of well-developed rift systems.

Moment Tensors of Ring‐Faulting at Active Volcanoes: Insights Into Vertical‐CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands

“…The Sierra Negra caldera renewed its eruption activity at ~19:40 on 26 June 2018 (UTC), which lasted until 23 August (Global Volcanism Program, 2018;Vasconez et al, 2018;Bell et al, 2021). The activity included eruptions from several fissure vents along the northern part of the caldera rim and on the…”

“…northern side of the volcanic flank, and large surface deformation with increased seismicity along the intra-caldera fault system (Bell et al, 2021). Prior to and during the eruption, two vertical-CLVD earthquakes with Mw > 5 were reported near the Sierra Negra caldera: a vertical-T earthquake with Mw 5.3 at 9:15 on 26 June, about 10 h before the initiation of the eruption, and a vertical-P earthquake with Mw 5.1 at 0:30 on 5 July.…”

“…We compare our estimations with geodetic observations by Bell et al (2021), who used GPS data recorded on the caldera floor. The authors reported that the vertical-T earthquake caused large co-seismic uplift of 1.8 m and 1.4 m at GPS stations GV09 and GV06, respectively (Figure 5b), which supports our estimation of the vertical-T earthquake along the southern fault.…”

“…Before and during the eruption, two vertical-CLVD earthquakes with M w > 5 were reported near the Sierra Negra caldera: a vertical-T earthquake with M w 5.3 at 9:15 on June 26, about 10 h before the initiation of the eruption, and a vertical-P earthquake with M w 5.1 at 0:30 on July 5. Bell et al (2021) analyzed GPS records at the caldera and attributed the two earthquakes to trapdoor faulting events on the intra-caldera fault structure. This indicates the ring-faulting origin of the earthquakes.…”

“…The black curve indicates the fresh vertical scarp identified byGeist et al (2008) during a field survey in June 2006; the part represented by the solid curve was clearly identified, whereas those along the dotted curves were less clearly defined. The red circles represent the locations of GPS stations used byBell et al (2021). The gray dotted curve indicates a possible geometry inferred in this study for the 2018 vertical-P earthquake (see Section 3.4).…”