Noneruptive Unrest at the Caldera of Alcedo Volcano (Galápagos Islands) Revealed by InSAR Data and Geodetic Modeling

Abstract

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 , 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.

Using Conceptual Models to Relate Multiparameter Satellite Data to Subsurface Volcanic Processes in Latin America

“…The uplift is classified as magma intrusion (Figure b) and is followed by a short period of rapid subsidence we attributed to local tectonic processes ( T ). This correlates well with the seismicity in the area observed by Davidge et al (), and the observations are consistent with the results of an InSAR and modeling study performed by Galetto et al (), which similarly identified intrusion and attributed the rapid episode of subsidence to rapid withdrawal and lateral magma migration.…”

The 2017 Noneruptive Unrest at the Caldera of Cerro Azul Volcano (Galápagos Islands) Revealed by InSAR Observations and Geodetic Modelling

“…Based on previous research in the Galápagos Archipelago, the Cerro Azul volcano has an irregular soup-bowl-shaped caldera, and the younger structure here produced a type of caldera similar to those of other volcanoes in the western Galápagos, which have deep trapdoors and potential ring faults with surrounding radial rifts [6,14,16,20,43,73]. Above all, magma systems with small volumes and great depths occur in these structures [6,20,30]. According to the joint deformation model in Section 5.1, Cerro Azul tends to possess a peculiar structure with two composite causal deformation sources at the similar depth on Galápagos Archipelago.…”

“…Repeated unrest events without eruption occurred in Alcedo from 1992 to 2011, where three of the events were all interpreted by the magma intrusion of platform-shaped sill deformation sources underground. A sill source model was adapted in the magma system, whose inflation was the origin of two events; the third was explained by the magma propagation from the current deflation sill to a new one [6]. The uplift event in the Fernandina volcano, on Fernandina Island, was presumed to be related to an inflation of a pipe-shaped magma chamber in 2012-2013 [46].…”

“…Volcanic tectonic activity can lead to a series of volcanic eruptions and deformation events, and so understanding internal magma sources is crucial for explaining the deformation and dealing with the disaster risks [1][2][3][4][5]. Volcanic unrest events, including seismic activity and degassing-frequently causing surface deformation-reflect unrest patterns and disturbances from internal pressure sources [6,7]. In a conceptual model, magma sources exist under volcano craters where surface deformation rates occurring with the activity largely depend on magma supply rates and storage depths [1, [8][9][10][11][12].…”

Bridging the Gap From Caldera Unrest to Resurgence

“…However, for a few other calderas, high resolution deformation time series spanning the last two or three decades are also available, providing a shorter but still valuable dataset. These resurgent calderas are felsic (Ischia, Italy; Long Valley, California; and Iwo Jima, Japan; Hill, 2006;Manzo et al, 2006;Ukawa et al, 2006;Ueda et al, 2018) or mafic (Sierra Negra and Alcedo; Galapagos) (Galetto et al, 2019, and references therein).…”