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Understanding paths of magma propagation is fundamental to infer how magma is transported from magma reservoir to the surface during eruptions. Here has been investigated the 2020 circumferential eruption that occurred on the upper east flank of Fernandina volcano (Galápagos), using Interferometric Synthetic Aperture Radar (InSAR) data and geodetic modelling. Results show that most of the deformation is related to a radial intrusion that propagated southward, evolving from sill-like intrusion beneath the caldera to radial and dike-like lower on the volcano flank. No deformation in the coherent area immediately to the east of the 2020 circumferential eruptive fissures is spatially correlated with these fissures, which might be associated with an ephemeral circumferential dike that have shared with the radial dike the same intra-caldera intruded sill. This eruption is the first documented event in the Galápagos where circumferential and radial dikes were intruded simultaneously, suggesting that magma in these volcanoes can propagate from the same intrusion in two different directions, with distinct geometries at the same time. The volume of the radial dike is higher than the inferred erupted volume. This fact suggests that magma mainly flowed into the radial dike, potentially explaining why the circumferential eruption only lasted for 9 h. [ABSTRACT FROM AUTHOR]

Previous work at Fernandina, the most active volcano of the Western Galápagos (Ecuador), revealed evidence for both a shallow and a deep magma reservoir, but the relative contribution of the two reservoirs to eruptions remains unclear. Here we investigate the September 2017 circumferential eruption and the June 2018 radial eruption using interferometric synthetic aperture radar data and geodetic modeling. Our results show that during the 2017 eruption magma was simultaneously withdrawn from the deep reservoir, injected upwards through the shallow reservoir, and then fed the circumferential feeder dike to the SW of the caldera. Two episodes of inflow of new magma occurred in both the deep and shallow magma reservoirs in the inter‐eruptive period from December 2017 to May 2018. During the 2018 eruption, both reservoirs fed two radial feeder dikes below the north flank, probably interacting with an underlying peripheral melt pocket, and an inclined sheet below the NW sector of the caldera. Our results highlight the primary role of the deeper reservoir which accumulates most of the magma before eruptions. Both eruptions were characterized by rapid magma transfer from the deeper to the shallower reservoir. This is similar to what is observed at the nearby Wolf volcano, but unlike nearby Sierra Negra, where a shallower reservoir accumulates higher volumes of magma before eruptions. These differences in the pre‐eruptive role of the deeper and shallower reservoirs might be related to the different evolutionary stages of Fernandina and Wolf with regard to the more mature Sierra Negra. Plain Language Summary: Fernandina is the most active volcano of the Western Galápagos (Ecuador). Two magma reservoirs at different depths below the volcano trigger eruptions both near the caldera rim (circumferential eruptions) and lower on the volcano flanks (radial eruptions). The role played by the two reservoirs in the eruptions is poorly understood. Here we studied the 2017 and the 2018 eruptions that occurred at Fernandina by using deformation data derived from radar satellites to investigate the inputs and outputs of new magma into the two reservoirs when eruptions occurred. The 2017 eruption had similar characteristics to the 2005 eruption, while the 2018 eruption had more complex mechanisms of shallow magma transfer, with magma transported in multiple directions below the north flank of Fernandina. We found that rapid magma transfer from the deep to the shallow reservoir provided most of the magma for both eruptions, similar to the nearby Wolf volcano, and unlike nearby Sierra Negra, a feature that may be due to the evolutionary stage of the volcanoes. Key Points: The 2017 circumferential eruption at Fernandina shows similar characteristics to the 2005 eruption, occurred in the same areaThe 2018 eruption is connected to the propagation of multiple dikes and sills, with most of the magma remaining intrudedBoth eruptions were characterized by rapid magma transfer from the deeper to the shallower reservoir, similar to what is observed at Wolf [ABSTRACT FROM AUTHOR]

Understanding volcanic unrest is crucial to forecasting eruptions. At active mafic calderas unrest culminates in eruption more frequently than at felsic calderas. However, the mafic caldera of Alcedo Volcano (Ecuador) has experienced repeated episodes of unrest without erupting, since at least 1992, when geodetic monitoring began. Here we investigate the unrest that occurred between 2007 and 2011 using interferometric synthetic aperture radar (InSAR) data and geodetic modeling. We observe an initial asymmetric uplift of the southern caldera floor (~30 cm of vertical motion) from 2007 to 2009, followed by subsidence of the uplifted area and contemporary uplift of the northwestern caldera rim between January and June 2010. Finally, from June 2010 through March 2011, caldera uplift resumed. The first uplift episode is best explained by inflation of a sill and the activation of an inner ring fault. Successive caldera subsidence and rim uplift are compatible with the withdrawal of magma from the previously inflated sill and its northwestern migration. The resumption of uplift is consistent with the repressurization of the sill. This evolution suggests episodic magma emplacement in a shallow reservoir beneath the caldera, with aborted lateral magma migration, probably due to the discontinuous supply from depth. This short‐term deformation pattern matches well geological observations showing a longer‐term (hundreds of years at least) asymmetric uplift of the caldera floor, culminating in a weak resurgence of ~30 m. We propose that the monitored episodes of uplift represent short‐term stages of the rarely observed incremental growth of a resurgent basaltic caldera. Key Points: The 2007‐2011 noneruptive unrest at Alcedo was caused by shallow emplacement of new magma with limited lateral intrusionUplift during unrest is similar in location and shape to the longer‐term weak resurgence of the calderaThis unrest provides the rare opportunity to document the incremental growth of a basaltic resurgent caldera [ABSTRACT FROM AUTHOR]

Calderas are impressive volcanic depressions commonly produced by major eruptions. Equally impressive is the uplift of the caldera floor that may follow, dubbed caldera resurgence, resulting from magma accumulation and accompanied by minor eruptions. Why magma accumulates, driving resurgence instead of feeding large eruptions, is one of the least understood processes in volcanology. Here we use thermal and experimental models to define the conditions promoting resurgence. Thermal modelling suggests that a magma reservoir develops a growing transition zone with relatively low viscosity contrast with respect to any newly injected magma. Experiments show that this viscosity contrast provides a rheological barrier, impeding the propagation through dikes of the new injected magma, which stagnates and promotes resurgence. In explaining resurgence and its related features, we provide the theoretical background to account for the transition from magma eruption to accumulation, which is essential not only to develop resurgence, but also large magma reservoirs. [ABSTRACT FROM AUTHOR]

Understanding volcanic unrest is crucial to forecasting eruptions. At active mafic calderas, unrest usually culminates in eruption, and does so more frequently than at felsic calderas. However, the mafic caldera of Alcedo Volcano (Ecuador) has experienced repeated episodes of unrest without erupting, since at least 1992, when geodetic monitoring began. Here, we investigate the unrest occurred between 2007 and 2011 performing a multi-temporal InSAR analysis of ENVISAT and ALOS-1 data, using the Small Baseline method. Then, we inverted ALOS-1 data to constrain the sources of deformation, using the GBIS software. We observe an initial asymmetric uplift of the caldera (~30 cm of vertical motion) from 2007 to 2009, followed by subsidence of the uplifted area and contemporary uplift of the north-western caldera rim between January and June 2010. Finally, from June 2010 through March 2011, caldera uplift resumed. The first uplift episode is best explained by inflation of a sill and the activation of an inner ring fault. Successive caldera subsidence and rim uplift are compatible with the withdrawal of magma from the previously inflated sill and its north-western migration. The resumption of uplift is consistent with the re-pressurization of the sill. This evolution suggests episodic magma emplacement in a shallow reservoir beneath the caldera, with aborted lateral magma migration, probably due to the discontinuous supply from depth. This short-term deformation pattern matches well geological observations showing a longer-term (hundreds of years at least) asymmetric uplift of the caldera floor, culminating in a weak resurgence of ~30 m. We propose that the monitored episodes of uplift represent short-term stages of the rarely observed incremental growth of a resurgent basaltic caldera. [ABSTRACT FROM AUTHOR]