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.

The 2015 eruption of Wolf volcano was one of the largest eruptions in the Galápagos Islands since the onset of routine satellite‐based volcano monitoring. It therefore provides an excellent opportunity to combine geophysical and petrological data, to place detailed constraints on the architecture and dynamics of subvolcanic systems in the western archipelago. We present new geodetic models that show that pre‐eruptive inflation at Wolf was caused by magma accumulation in a shallow flat‐topped reservoir at ~1.1 km, whereas edifice‐scale deformation during the eruption was related to a deflationary source at 6.1–8.8 km. Petrological observations suggest that the erupted material was derived from both a subvolcanic mush and a liquid‐rich magma body. Using a combination of olivine‐plagioclase‐augite‐melt (OPAM) and clinopyroxene‐melt barometry, we show that the majority of magma equilibration, crystallization, and mush entrainment occurred at a depth equal to or greater than the deep geodetic source, with little petrological evidence of material sourced from shallower levels. Hence, our multidisciplinary study does not support a fully transcrustal magmatic system beneath Wolf volcano before the 2015 eruption but instead indicates two discrete storage regions, with a small magma lens at shallow levels and the major zone of magma storage in the lower crust, from which most of the erupted material was sourced. A predominance of lower crustal magma storage has previously been thought typical of subvolcanic systems in the eastern Galápagos Archipelago, but our new data suggest that this may also occur beneath the more active volcanoes of the western archipelago.

Forecasting future activity and performing hazard assessments during the reactivation of large andesitic volcanoes remain a great challenge for the volcanological community. On August 14, 2015 Cotopaxi volcano erupted for the first time in 73 years after approximately four months of precursory activity, which included an increase in seismicity, gas emissions, and minor ground deformation. Here we discuss the use of near real-time petrological monitoring of ash samples as a complementary aid to geophysical monitoring, in order to infer eruption dynamics and evaluate possible future eruptive activity at Cotopaxi. Twenty ash samples were collected between August 14 and November 23, 2015 from a monitoring site on the west flank of the volcano. These samples

After eight years of quiescence, Fernandina volcano experienced two short-lived eruptions, on 4 September 2017 and 16 June 2018. The eruptions were characterized by very short periods of unrest that started a few hours before the initiation of the eruptive activity. On the other hand, Sierra Negra volcano (Isabela Island) began a new eruptive period on 26 June 2018, after almost one year of persistent unrest characterized by an increase in the magnitude and number of seismic events and more than 5 meters of uplift since its last eruption in 2005. The Sierra Negra and Fernandina eruptions were located in remote zones where access is extremely complex. Thus, satellite images complement the continuous monitoring data of the Instituto Geofísico (IG-EPN) with remote observations and allow rapid response mapping in order to identify the areas affected by the lava flows. Finally, the aim of this Report is to encourage other scientists to investigate the behaviors of both pre-eruptive and eruptive periods registered during these eruptions. ResumenDespués de ocho años de reposo, el volcán Fernandina experimentó dos periodos eruptivos de corta duración, el 4 de Septiembre del 2017 y el 16 de Junio del 2018. Dichas erupciones se caracterizaron por etapas muy cortas de agitación que iniciaron pocas horas antes de la erupción. Por otro lado, el volcán Sierra Negra, localizado en la Isla Isabela, inició un nuevo periodo eruptivo el 26 de Junio del 2018, después de casi un año de persistente agitación caracterizada por el incremento en la magnitud y número de eventos sísmicos y más de cinco metros de levantamiento del piso de la caldera desde su última erupción en 2005. Las erupciones de Sierra Negra y Fernandina se localizaron en zonas remotas, donde el acceso es extremadamente difícil. Es así que, imágenes satelitales complementaron el monitoreo continuo realizado por el Instituto Geofísico (IG-EPN) y permitieron identificar las zonas afectadas por los flujos de lava. Finalmente, uno de los propósitos de este reporte es alentar a otros científicos a investigar el funcionamiento de estos volcanes durante las etapas pre-eruptivas y eruptivas registradas.

No abstract