Fringe 2017 > Session details
Paper 97 - Session title: Volcanoes
14:00 Deformation at the Rabaul caldera, Papua New Guinea modelled using ALOS PALSAR and GPS time series
Garthwaite, Matthew (1); Saunders, Steve (2); Hu, Guorong (1); Parks, Michelle (3) 1: Geoscience Australia, Australia; 2: Rabaul Volcano Observatory, Papua New Guinea; 3: University of Iceland, Iceland
The Rabaul caldera is an active Pleistocene to recent volcanic complex on the north-eastern point of New Britain Island, Papua New Guinea (PNG). It contains several small Holocene eruptive centres within the footprint of a large nested caldera structure. In the last ~200 years these small volcanoes have erupted on average every 20-60 years. Historically the most active are Tavurvur and Vulcan, located within the Rabaul harbour. The Rabaul caldera represents the highest risk of all PNG volcanoes since the town of Rabaul is located within the caldera structure. A significant twin eruption of the Tavurvur and Vulcan vents occurred in 1994 that destroyed large parts of the town and resulted in five casualties. Since 1994 Vulcan has remained dormant, but a major eruption occurred at Tavuvur on 6 October 2006. A simultaneous drop in surface height of nearly 30 cm was observed in GPS data collected at Matupit Island, the closest land mass to the centre of the main sub-caldera magma chamber. Following this eruption, a period of almost continuous minor eruptions of Tavuvur ensued, accompanied by a non-linear subsidence signal. These eruptions ceased at the beginning of 2010, at which time subsidence changed to uplift. Uplift prevailed until another significant eruption of Tavuvur on 29 August 2014, when an instantaneous subsidence of ~7 cm was observed.
We have processed 21 ALOS PALSAR fine-beam SAR images acquired between 27 February 2007 and 10 March 2011 using the GAMMA software. L-band data is required in the highly vegetated environment of PNG to overcome temporal decorrelation that affects shorter wavelength data such as Sentinel-1. Analysis of continuous GPS data from four stations within the caldera was undertaken using the scientific Bernese software V5.2 with solutions tied to the ITRF2008 reference frame. We perform a joint inversion of a connected network of 20 interferograms and the continuous GPS observations to determine the temporal variation in volume change for the best-fitting Mogi point-source model of the deformation field. The weighted least squares inversion is solved using Singular Value Decomposition where the weights are derived from noise within each interferogram in the far field of the caldera. The spatially dense InSAR observations are subsampled in order to enable an efficient computation on desktop machines. The procedure involves first conducting coarse and fine grid searches over 3-dimensional space to find the best-fitting source location. Once the minimum has been located the temporal variation in volume change of the source is estimated.
The best fitting Mogi point source location is situated south of Matupit Island and north-west of Vulcan at 4.26°S, 152.18°E at a depth of 4.5 km, which is well within the geophysically-imaged sub-caldera magma chamber. We find that the inferred volume change for this source amounts to a deflation rate of ~10x106 m3 yr-1 during 2008 and 2009 and an inflation rate (uplift) of ~7x106 m3 yr-1 during 2010 and early 2011. Transient deformation signals in the interferograms localised around the Tavuvur vent may be useful in helping to derive a better understanding of the plumbing system connecting the magma chamber with the eruptive centres. This in turn may enhance short term eruption prediction. The Rabaul Volcano Observatory (RVO) is responsible for issuing eruption alerts for all PNG volcanoes. Future work to apply InSAR analysis on a national scale will assist the RVO to monitor the eruptive state of other active volcanoes that otherwise remain un-monitored.
Paper 206 - Session title: Volcanoes
15:00 Deformation monitoring for the Ecuadorian Volcano Geohazard Supersite
Amelung, Falk; Morales Rivera, Anieri; Mothes, Patricia; Zhang, Yunjun; Terrero, Alfredo University of Miami, United States of America
The Ecuadorian volcanoes have been selected by the Group on Earth Observation (GEO) as a volcano Supersite as part of the Geohazard Supersite and Natural Laboratory initiative (GSNL). Several space agencies provide SAR data for routine monitoring of the volcanoes for disaster mitigation. Here we present the infrastructure put in place for the Supersite and results obtained for the Ecuadorian volcanoes with emphasis on the 2015 crises of Cotopaxi volcano. A new episode of unrest started in April of 2015, with increasing seismicity, degassing, and deformation which led to a new eruptive phase in August 2015. This was the first eruption after nearly 73 years of quiescence. We present deformation data obtained using the COSMO-SkyMed satellite system of the Italian Space Agency and using TerraSAR-X of the German Aerospace Agency using the Small Baseline (SB) method, using the PySAR software. The InSAR data products are available from http://insarmaps.rsmas.miami.edu.
Paper 262 - Session title: Volcanoes
14:40 The 2015 Wolf volcano (Galápagos) eruption: source modeling of Sentinel 1-A DInSAR deformations
De Novellis, Vincenzo; Castaldo, Raffaele; De Luca, Claudio; Pepe, Susi; Zinno, Ivana; Casu, Francesco; Lanari, Riccardo; Solaro, Giuseppe IREA-CNR, Italy
We analyze the surface deformation of Wolf volcano imaged through satellite Differential Synthetic Aperture Radar Interferometry (DInSAR) in order to search for the causative source responsible for the May-July 2015 eruption. Following 33 years of quiescence, the volcano has experienced several historical eruptions: the 1797 eruption is the first documented one; later, 11 eruptions were recorded between 1900 and 2015 often from the SE vent area. However, due to the limited amount of scientific works on the Wolf volcano, and to better understand the recent historical volcano dynamics and thoroughly constrain the geometry and characteristics of the main deformation source, we also benefit from the availability of the C-band space-borne SAR acquisition of the ENVISAT-ASAR sensor that imaged the volcano during the 2004-2010 time period. In particular, we perform an inversion of the 2004-2010 ENVISAT DInSAR deformation time series, computed through the Small BAseline Subset (SBAS) approach applied to the SAR data sequences acquired from ascending and descending orbits, in order to discriminate the main source type (e.g., sill-like body or spheroid). These measurements allow us to focus on the recent volcano dynamics and to constrain the geometry and characteristics of the main deformation source. In this first step an horizontal sill-like source at a depth of about 1.5 km below the caldera floor exists; it opens (inflation) at rate of 0.036 cm/yr yielding to a dominant surface uplift of the summit caldera of about 2.5 cm/yr.
The results suggest that a sill-like source, 2.5 km long, 2.0 km wide and located at depth of about 1.5 km from the caldera floor, better fits the observed uplift and E-W pattern, in good agreement with other studies that highlight the existence of a flat-topped shallow source.
The inversion of the DInSAR measurements related to the May-July 2015 Wolf volcano eruption, reveals the presence of multiple sources of deformation active at different times and locations. In particular, we invert two Sentinel 1-A DInSAR maps, encompassing the May-July 2015 eruption, that reveal the presence of multiple sources of deformation, implying the existence of a complex magmatic system rather than a system formed by a single magma chamber. We find that two deformation sources are responsible for the observed deformations: a deeper sill-like source and a nearly vertical dike. More specifically, during the 1st phase of the eruption (from May to mid June 2015) the dike beneath the SE edge of caldera rim opens of about 160 cm, permitting the magma to flow on the surface; the magma is withdrawn from the horizontal sill-like source. During the 2nd eruptive phase (mid June to mid July 2015), a very significant deflation is revealed; in this case the eruption activity, rather than from the fissure vents that opened on the upper SE flank on May 25, migrates inside the caldera floor where a new vent opened, hence a possible simultaneous eruption occurred.
This fact implies the existence of a complex magmatic geometry rather than a system formed by a single magma chamber. In particular, our results highlight an interplay between the type and number of deformative sources and the detected patterns of surface deformation. Our modeling result accounts for two active deformation sources: i) a nearly vertical dike beneath the SE edge of caldera rim and ii) an horizontal deeper sill source of inflation/deflation centred beneath the caldera. Practically, the dike becomes active feeding the eruptive circumferential fissure of the May 25, 2015 eruptive event, it opens of about 160 cm on the SE rim, permitting the magma to flow to the surface; the magma is withdrawn from the deepest horizontal sill-like source, generating in turn a deflation of about 40 cm.
Paper 322 - Session title: Volcanoes
14:20 Is a pipe-like the geodetic source responsible of the detected volcanic unrest phenomena occurred in two different geodynamic contexts? Galapagos and Hawaii case studies.
Pepe, Susi (1); Castaldo, Raffaele (1); Casu, Francesco (1); D'Auria, Luca (1,2,3); de Luca, Claudio (1); De Novellis, Vincenzo (1); Solaro, Giuseppe (1); Tizzani, Pietro (1) 1: Istituto per il Rilevamento Elettromagnetico dell'Ambiente (Irea), CNR, Italy; 2: Instituto Volcanológico de Canarias (INVOLCAN), Puerto de la Cruz, S/C Tenerife, Canary Islands, Spain; 3: Instituto Tecnológico y de Energías Renovables (ITER), Environmental Research Division, S/C Tenerife, Canary Islands, Spain
We investigated the source of the ground deformation affecting the Fernandina (Galapagos) and Mauna Loa (Hawaii) volcanoes by jointly exploiting different datasets collected by both GPS and multiplatform and multiorbit SAR sensors. We exploited the advanced Differential SAR Interferometry (DInSAR) techniques to analyze unrest episodes in two different geodynamics context.
In the case of Fernandina Volcano (Galápagos) we exploited the advanced Differential SAR Interferometry (DInSAR) techniques to analyze the 2012-2013 uplift episode by using X-band data from the COSMO-SkyMed (CSK) satellite constellation. This volcano falls among those which are not well monitored, therefore, the availability of CSK data, acquired with a repeat time ranging from 4 to 12 days and with a ground resolution of 3 meters, represents a unique opportunity to perform a detailed study of the space and time ground deformation field changes (Sansosti et al., 2014). In addition, in this case study we computed the ground deformation time series by applying the Small BAseline Subset (SBAS)-DInSAR approach (Berardino et al., 2002) to CSK data, acquired from both ascending and descending orbits. The results of their combination (vertical and horizontal E-W components) are used in order to evaluate, through a cross correlation analysis (Tizzani et al., 2009; 2015), the volcanic areas that are characterized by similar uplift temporal behavior. Subsequently, we determine the geometry, location and the temporal evolution of the geodetic source responsible for the 2012 - 2013 uplift event by applying an inverse method to the DInSAR measurements. We search for its geometrical parameters and volume variation that minimize the difference between the observed data and the modelled ground deformation field. We tested various analytical models: the Mogi point source (Mogi, 1958), the sphere (McTigue, 1987), the penny-shaped crack (Fialko, 2001), the vertical closed pipe (Bonaccorso and Davis, 1999), a sub-vertical, horizontal and inclined crack (Okada, 1985), a prolate ellipsoid and tilted closed pipe-like pressurized source (after Yang et al., 1988). Finally, using the Akaike Information Criterion (Akaike, 1965) among the tested analytical sources, we selected the tilted pipe. The pipe model is similar to the prolate ellipsoid, but the size of the smaller axis is kept fixed to a very small value (i.e., 10 m). Despite having a similar fit with the prolate ellipsoid, the tilted pipe-like source has been selected because it has a lower number of degrees of freedom. Both vertical and E-W cross-correlated maps support the hypothesis of the existence of a single active source, characterized by a spatial stability over the entire considered time interval. Indeed, with the proposed source inversion procedure, we have shown that the inflation of a SE dipping tilted closed pipe-like pressurized source explains the observed ground deformation pattern very well. This result suggests that the observed uplift phenomenon could be produced by the progressive pressurization of a shallow elongated magma chamber, before the eruption onset phase.
The deformation time series of Mauna Loa volcano comes from 23 GPS permanent stations of the Hawaii surveillance network, processed by Nevada Geodetic Laboratory, 7 SAR dataset acquired from ascending and descending orbits, with different look angles and along different tracks and by the C-Band Envisat satellite along the 2003 – 2010 time period for a total of 189 SAR imagery. Moreover, we exploited 2 datasets collected from ascending and descending passes by the X-Band Cosmo Sky-Med constellation during the 2012 – 2015 time span. These SAR datasets have been processed through the advanced DInSAR technique referred to as P-SBAS (De Luca et al., 2016), which allows us to retrieve the Line of Sight (LOS) projection of the surface deformation and analyze its temporal evolution by generating displacement time series. Starting this data collection, we determined the source responsible of observed ground deformation considering and comparing different source models.The results of our inversions did not show any significant contribution of a spheroidal volumetric source to the observed ground deformation pattern. In fact, its presence does not affect significantly the final cost function of the best fit model. Conversely, a pipe source, as well as a dike system and a basal decollement contributes substantially to both the ground deformation pattern.
Finally, our main goal is the understanding of the relationship among the spatio-temporal evolution of the ground deformation field and the temporal volumetric variation of the detected geodetic source during the uplift phenomena. We highlight the huge opportunity in understanding volcano unrest phenomena offered by the joint use of remote sensing data and inversion procedures: this prospect is particularly relevant for the analysis of uplift events, when other geophysical measurements are not available. In both cases, the performed statistic analysis support the source pipe-like as the more suitable geometry to explain the unrest phenomena in which magmatic masses intrude in volcanic conduits.
This work has been supported by the Italian Department of Civil Protection, the Italian Space Agency (ASI) within the SAR4Volcanoes project (agreement I/034/524 11/0) and it is part of the CEOS Volcano Pilot project (http://ceos.org/ourwork/workinggroups/disasters/volcanoes/), DTA. AD004.065.001 Geophysics, Project CNR _PDGP 2016-2018 the European Union Horizon 2020 research and innovation programme under grant agreement No 676564, the ESA GEP (Geohazards Exploitation Platform), I-AMICA (Infrastructure of High Technology for Environmental and Climate Monitoring - PONa3_00363) projects. Sentinel-1 data are copyright of Copernicus (2016). The DEMs of the investigated zone were acquired through the SRTM archive.
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Paper 548 - Session title: Volcanoes
15:20 Round Table Discussion
All, All ESA, Italy