Posteruptive Deformation Research Articles

New insights into the Jurassic polyphase strain partition on the patagonian back-arc; constraints from structural analysis of ancient volcanic structures

Located in the western Northpatagonian region, Argentina, the Lower Jurassic Cañadón Chileno Complex (CCHC) provides a remarkable opportunity to assess the roles of pre-, syn-, and post-eruptive faulting in felsic diatremes complexes evolution. The structural analyses of fractures, dikes, and folds allow recognition of the occurrence of four different strain partitions (SP1-SP4) developed during the Lower to Middle Jurassic. Recognized strain configurations show equivalent temporal and structural relationships throughout the Jurassic back-arc system of Patagonia and contemporary basins of southern South America. The stratigraphical criteria allow inferring an Upper Sinemurian to Lower Pliensbachian time interval for the initial strain configurations (SP1, SP2, and SP3). WNW, NNE, and NE-oriented extensional phases were defined and correlated with adjoining areas. Particularly, the third strain partition phase is characterized by a significant transpressive deformation. A NE contractional episode characterizes the post-eruptive deformation stage (SP4) during the Bajocian to Callovian interval. Tectonic interpretations were elaborated concerning subduction dynamics, continental drift, and rotation that controlled the regional and local stress configuration throughout the Jurassic Period of Patagonia and central Argentina.

Modeling the Posteruptive Deformation at Okmok Based on the GPS and InSAR Time Series: Changes in the Shallow Magma Storage System

AbstractBased on the unscented Kalman filter, we develop a time‐dependent inversion filter combining Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) time series observations for modeling volcano deformation. We use the Variance Component Estimation method as means to assign the relative weights for GPS and InSAR data. Then we use the inversion filter to model the posteruptive deformation at Okmok volcano, Alaska. We find that a Mogi source at 3–4 km depth fits the InSAR data well, while the best fit to the GPS data is an oblate spheroid source at about 2.5 km depth. Our final model consists of a shallow sill at ~0.9 km and a Mogi source at ~3.2 km depth, which well fit both the GPS and InSAR data simultaneously. We think the Mogi source obtained here is the same source account for the preeruptive deformation. The shallow sill is a new structure that was not seen before the 2008 eruption. From 2008 to 2019, we have observed five inflation episodes, each of which decays exponential in time. We find that the characteristic timescale of those inflation episodes decreases with respect to time. The total volume change from the two sources is 0.068 km3, which recovers 50–60% of the volume decrease during the 2008 eruption.

Posteruptive Thermoelastic Deflation of Intruded Magma in Usu Volcano, Japan, 1992–2017

AbstractSecular ground subsidence at Usu volcano (Japan) has been reported around the eruption vents following the four eruptions in 1910, 1943, 1977, and 2000. However, the mechanisms accounting for the subsidence have not been well understood. In this study, we systematically investigated the posteruptive deformation at Usu volcano using interferometric synthetic aperture radar based on 111 JERS, ALOS‐1, and ALOS‐2 images acquired from 1992 to 2017. We also calculated quasi east‐west and vertical ground displacements between 2006 and 2017. Our results show three localized deformation regions from west to east of Usu volcano with their locations corresponding to the 2000, 1977, and 1943 eruption vents, respectively. All the deformation sites show patterns of east‐west contraction and subsidence. The extent and rate of posteruptive subsidence declined dramatically at the vent of the 2000 eruption site from 2006 to 2017, decreased gradually at the 1977 vent, and show a steady pattern for the 1943 site during 1992–2017. We ascribed the observed posteruptive subsidence to thermoelastic contraction of a sphere intruded at the time of the eruptions to constrain locations, depths, and volumes of heat sources with the assumption of the spherical source shapes. Thermoelastic modeling reveals that the heat sources are embedded at shallow depths not deeper than 400 m below sea level with volumes of about (8.72 ± 0.19) × 106, (132.18 ± 5.21) × 106, and (49.51 ± 2.02) × 106 m3 for the 2000, 1977, and 1943 eruption sites, respectively. The modeling also highlights the importance of underground water in assessing the thermal diffusion process and the associated posteruptive deformation.

Co-eruptive subsidence and post-eruptive uplift associated with the 2011–2012 eruption of Puyehue-Cordón Caulle, Chile, revealed by DInSAR

The 2011–2012 eruption of the Puyehue-Cordón Caulle volcanic complex, southern Andes (Chile), was associated with complex surface deformation affecting an area of roughly 50 by 50km. We report here differential SAR interferometry (DInSAR) results of pre-, co- and post-eruptive deformation from ENVISAT ASAR, COSMO-Skymed, and ALOS-2/PALSAR scenes acquired between early 2011 and early 2017. No clear pre-eruptive deformation is observed during five months before the eruption, although some patterns could be interpreted as showing inflation occurring between April and May 2011. Co-eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe (120cm LOS lengthening) centered 10km NW of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent. Re-inflation began immediately after the end of the eruption. A first pulse lasted 3years between 2012 and 2015, accumulating ~70cm uplift. We detect here a second pulse, beginning in June 2016 and still ongoing in February 2017, reaching 12cm in half a year. Inverse modeling with spherical cavity and spheroidal sources locates re-inflation sources at a depth ranging between 8 and 11km under the surface. It suggests re-filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011–2012 eruption.

Using ignimbrites to quantify structural relief growth and understand deformation processes: Implications for the development of the Western Andean Slope, northernmost Chile

Large-volume ignimbrites are excellent spatial and temporal markers for local deformation and structural relief growth because they completely inundate and bury the underlying paleotopography and leave planar surfaces with relatively uniform, low-gradient slopes dipping less than 2°. Using one of these planar surfaces as a reference frame, we employed a line-balanced technique to reconstruct the original morphology of an ignimbrite that has undergone postemplacement deformation. This method allowed us to constrain both the amount of posteruptive deformation and the topography of the pre-eruptive paleolandscape. Our test case was the unwelded surface of the 21.9 Ma Cardones ignimbrite, located on the western slope of the Central Andes in northernmost Chile (18°20′S). By reconstructing the original surface slope of this ignimbrite, we demonstrate that the pre–21.9 Ma topography of the Western Andean Slope was characterized by structural relief growth and erosion in the east, and the creation of accommodation space and sedimentation in the west. The paleoslope at that time was dissected by river valleys of up to 450 ± 150 m deep that accumulated great thicknesses (>1000 m) of the Cardones ignimbrite, and likely controlled the location of the present-day Lluta Quebrada as a result of differential welding compaction of the ignimbrite. Our reconstruction suggests that growth of the Western Andean Slope had already started by ca. 23 Ma, consistent with slow and steady models for uplift of the Central Andes. Subsequent deformation in the Miocene generated up to 1725 ± 165 m of structural relief, of which more than 90% can be attributed to fault-related folding of the ∼40-km-wide Huaylillas anticline. Uplift related to regional forearc tilting is less than 10% and could have been zero. The main phase of folding likely occurred in the mid- to late Miocene and had ceased by ca. 6 Ma.

Crustal deformation associated with the 2011 eruption of the Nabro volcano, Eritrea

We investigate the crustal deformation associated with the 2011 eruption of the Nabro volcano, Afar, Eritrea. The Nabro volcano erupted on the night of 12 June 2011. A seismic sequence started 5h before the onset of the volcanic eruption. It included 25M>3 earthquakes, of which one Mw 5.6 normal fault earthquake occurred on 12 June at about the same time as the onset of the eruption, and one Mw 5.6 strike-slip earthquake occurred at the end of the main sequence on 17 June. The deformation associated with the eruption and the seismic activity was resolved by Interferometric Synthetic Aperture Radar (InSAR) measurements of the TerraSAR-X and ENVISAT satellites. Interferograms were generated using ascending and descending track pairs. The Nabro caldera and the associated channel of magma flow are characterized by significant loss of coherence which limited our InSAR observations at the near field of the volcano. Therefore, detailed assessment of co- and post-eruptive seismicity and monitoring of post-eruptive deformation using continued InSAR observations were added to the co-eruptive analysis in order to better constrain the different magmatic and tectonic components and determine the final source model. We carried out tens of different inversion models. Our best-fit model includes a dike, a normal fault and a strike-slip fault, consistent with the mechanisms of the major earthquakes. Coulomb stress calculations based on our model are found to be in agreement with post-eruptive seismicity. Finally, the source mechanism and geometry of our model are found to be in accord with the major tectonic structures in this area.

Localization of magma injections, hydrothermal alteration, and deformation in a volcanic detachment (Piton des Neiges, La Réunion)

This contribution aims at understanding how magmatism, hydrothermal alteration, and deformation may have interacted to localize a detachment (a low-angle normal fault) in a basaltic volcano. Piton des Neiges, an inactive volcano of La Réunion Island, has been deeply cut by erosion, allowing its inner structure to be investigated. The deepest unit observed in the edifice is a kilometer-scale plutonic complex, the top of which is intruded by multiple sills. This zone of repeated sill intrusions has been interpreted as a detachment because it displays evidence of hydrothermal alteration in the greenschist facies linked to a brittle-ductile shear deformation. Deformation begins with cataclasis and is followed by mylonitization and chlorite crystallization, then by hydrofracturing and pumpellyite crystallization. Subsequent and post-deformation calcite crystallization occurs in voids such as fractures and vacuoles. Aluminium substitutions in chlorite suggest that the syn-deformation hydrothermal alteration did not exceed 250°C and peaked in the deformation zone. Comparison of bulk-rock major element analyses of fresh, altered and deformed rocks shows that the zone of sill intrusion and deformation localized increased concentrations of P and K otherwise depleted in the footwall and hangingwall rocks, suggesting that the detachment acted as a trap for fluids.In contradiction with proposed models of volcano spreading, it is apparent that the portion of Piton des Neiges accessible to observation did not deform by creep of a large hydrothermal system or a plutonic complex below its solidus. Instead, the interface between the already cooled plutonic complex and the host rock acted as a brittle failure zone and was repeatedly intruded by magma injections. This localized heat source promoted hydrothermal alteration and low temperature creep in and around the discontinuity. The same process of magmatism-related weakening might occur on active volcanoes; it may, for instance, explain the slow post-eruptive deformation of the eastern flank of Piton de La Fournaise (the active volcano of La Réunion) observed since the April 2007 eruption.

Post-Eruption Deformation Processes Measured Using ALOS-1 and UAVSAR InSAR at Pacaya Volcano, Guatemala

Pacaya volcano is a persistently active basaltic cone complex located in the Central American Volcanic Arc in Guatemala. In May of 2010, violent Volcanic Explosivity Index-3 (VEI-3) eruptions caused significant topographic changes to the edifice, including a linear collapse feature 600 m long originating from the summit, the dispersion of ~20 cm of tephra and ash on the cone, the emplacement of a 5.4 km long lava flow, and ~3 m of co-eruptive movement of the southwest flank. For this study, Interferometric Synthetic Aperture Radar (InSAR) images (interferograms) processed from both spaceborne Advanced Land Observing Satellite-1 (ALOS-1) and aerial Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data acquired between 31 May 2010 and 10 April 2014 were used to measure post-eruptive deformation events. Interferograms suggest three distinct deformation processes after the May 2010 eruptions, including: (1) subsidence of the area involved in the co-eruptive slope movement; (2) localized deformation near the summit; and (3) emplacement and subsequent subsidence of about a 5.4 km lava flow. The detection of several different geophysical signals emphasizes the utility of measuring volcanic deformation using remote sensing techniques with broad spatial coverage. Additionally, the high spatial resolution of UAVSAR has proven to be an excellent compliment to satellite data, particularly for constraining motion components. Measuring the rapid initiation and cessation of flank instability, followed by stabilization and subsequent influence on eruptive features, provides a rare glimpse into volcanic slope stability processes. Observing these and other deformation events contributes both to hazard assessment at Pacaya and to the study of the stability of stratovolcanoes.

Multi-sensor data fusion for remote sensing of post-eruptive deformation and depositional features at Redoubt Volcano

Monitoring volcanic activity by remote sensing is an essential component of volcanology. Remote sensing includes a variety of different sensing methods and instruments that collect data across a wide range of the electromagnetic spectrum. This study presents an overview of the improvements that are available to remote sensing imaging with multi-sensor and multi-temporal data fusion of optical and radar data, using Redoubt Volcano and related 2009 Drift River lahar deposits as a target area. From ALOS-PRISM data, high resolution DEMs were produced and used to generate elevation change maps of Redoubt Volcano and the Drift River, and to estimate the volcano's dome volume; these DEMs were then fused with ALOS-PALSAR radar images to produce differential interferograms demonstrating the effect of high-resolution DEMs on surface deformation measurements from interferometric radar data; and finally, multi-temporal InSAR coherence data were used to plot the boundaries of lahar flows at the distal end of the Drift River with high accuracy. These techniques demonstrate: (1) how the fusion of data from multiple sensors acquired at multiple temporal intervals can substantially increase the accuracy and precision of remote sensing measurements compared to those from one sensor alone; (2) how data fusion techniques can improve remote sensing change detection in areas otherwise ill-suited for single sensor observations; and (3) how data subject to temporal decorrelation may be used for boundary mapping with high accuracy. In addition to volcanic deformation, these methods can be applied to a number of disciplines, and will become more essential as the number of earth observing satellites increase.

Physics-based models of ground deformation and extrusion rate at effusively erupting volcanoes

[1] We present a model of effusive silicic volcanic eruptions which relates magma chamber and conduit physics to time-dependent data sets, including ground deformation and extrusion rate. The model involves a deflating chamber which supplies Newtonian magma through a cylindrical conduit. Solidification is approximated as occurring at fixed depth, producing a solid plug that slips along its margins with rate-dependent friction. Changes in tractions acting on the chamber and conduit walls are used to compute surface deformations. Given appropriate material properties and initial conditions, the model predicts the full evolution of an eruption, allowing us to examine the dependence of observables on initial chamber volume, overpressure, and volatile content. Employing multiple data sets in combination with a physics-based model allows for better constraints on these parameters than is possible using kinematic idealizations. Modeling posteruptive deformation provides an improved constraint on the rate of influx into the magma chamber from deeper sources. We compare numerical results to analytical approximations and to data from the 2004–2008 eruption of Mount St. Helens. For nominal parameters the balance between magma chamber pressure and frictional resistance of the solid plug controls the evolution of the eruption, with little contribution from the fluid magma below the idealized crystallization depth. While rate-dependent plug friction influences the time-dependent evolution of the eruption, it has no control on the final chamber pressure or extruded volume.

Quasi-static thermoelastic deformation in an elastic half-space: theory and application to InSAR observations at Izu-Oshima volcano, Japan

SUMMARY We derive closed analytical solutions for quasi-static thermoelastic deformation in response to instantaneous point and spherical heat sources in an elastic half-space. Since we can take advantage of the solutions for an infinite medium, the derivation of solutions for a semi-infinite medium is straightforward. We examine the spatial and temporal evolution of thermoelastic deformation for point and spherical heat sources. We applied the solution to a radar interferometric observation of post-eruptive deformation associated with the 1986 fissure eruption at Izu-Oshima volcano, Japan. Assuming a spherical heat source at a depth of 240 m with a volume of 1.15 × 10 7 m 3 and a temperature step 10 3 K, the predicted rate of post-eruptive ground movement agrees with the observed rate within observational errors. Also, the same parameter values allow us to compute the co-eruptive ground displacement by the effect of mass intrusion, whose amplitude is consistent with the observed height (45 m) of the newly formed cone. The derived solutions can be applied to transient ground displacements observed at active volcanoes, and allow us to evaluate the heat amount of magma intruded at very shallow depths.

Transient volcano deformation sources imaged with interferometric synthetic aperture radar: Application to Seguam Island, Alaska

Thirty interferometric synthetic aperture radar (InSAR) images, spanning various intervals during 1992–2000, document coeruptive and posteruptive deformation of the 1992–1993 eruption on Seguam Island, Alaska. A procedure that combines standard damped least squares inverse methods and collective surfaces, identifies three dominant amorphous clusters of deformation point sources. Predictions generated from these three point source clusters account for both the spatial and temporal complexity of the deformation patterns of the InSAR data. Regularized time series of source strength attribute a distinctive transient behavior to each of the three source clusters. A model that combines magma influx, thermoelastic relaxation, poroelastic effects, and petrologic data accounts for the transient, interrelated behavior of the source clusters and the observed deformation. Basaltic magma pulses, which flow into a storage chamber residing in the lower crust, drive this deformational system. A portion of a magma pulse is injected into the upper crust and remains in storage during both coeruption and posteruption intervals. This injected magma degasses and the volatile products accumulate in a shallow poroelastic storage chamber. During the eruption, another portion of the magma pulse is transported directly to the surface via a conduit roughly centered beneath Pyre Peak on the west side of the island. A small amount of this magma remains in storage during the eruption, and posteruption thermoelastic contraction ensues. This model, made possible by the excellent spatial and temporal coverage of the InSAR data, reveals a relatively simple system of interrelated predictable processes driven by magma dynamics.

Sea level changes from Topex‐Poseidon altimetry and tide gauges, and vertical crustal motions from DORIS

Sea level difference (Topex‐Poseidon minus tide gauge) time series have been computed over 1993–1997 at 53 selected gauges sites. Comparison of these sea level differences with vertical crustal motions derived from the DORIS space geodesy system at 6 colocated sites shows good consistency. At one site (the Socorro volcanic island), a striking correlation is reported between sea level differences and DORIS height time series. The observed trend likely reflects a post eruptive deformation associated with a volcanic eruption that occurred in early 1993. At several other gauge sites, the sea level differences present large linear trends possibly bearing evidence of land motion. This may be the case at Rabaul (Papua New Guinea) where a volcanic eruption took place in autumn of 1994. The sea level differences at Rabaul show a negative trend from this date, likely related to the volcanic event.