The CEOS Pilot Project, Satellite Volcano Monitoring in Latin America and New Insar Ground Deformation Results at Llaima, Villarrica and Calbuco Volcanoes

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F u n 2 d 6 la serena octubre 2015 ada en 19 The CEOS pilot project, satellite volcano monitoring in Latin America and new InSAR ground deformation results at Llaima, Villarrica and Calbuco volcanoes

Francisco Delgado*, Matthew E. Pritchard Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA Susanna Ebmeier, Juliet Biggs, David Arnold School of Earth Sciences, University of Bristol, Bristol, UK Pablo González School of Earth and Environment, University of Leeds, Leeds, UK Michael Poland Cascades Volcano Observatory, United States Geological Survey (USGS), Vancouver, Washington, USA Simona Zoffoli Agenzia Spaziale Italiana (ASI), Rome, Italy. Loreto Córdova, Luis E. Lara Observatorio Volcanológico de los Ands del Sur (OVDAS), SERNAGEOMIN, Temuco, Chile

*Contact email: [email protected] monitoring agencies in Latin American countries would directly benefit from the resources that this pilot will Abstract. We present results from the 3-year CEOS volcano pilot project, which aims to monitor all Latin America 315 Holocene volcanoes at least 4 times/year make available. It is hoped that the regional study will and the ~50 erupting or deforming volcanoes at least demonstrate that Earth observation data can help to monthly. The pilot will incorporate satellite observations to identify volcanoes that may become active in the future track deformation, gas, ash, and thermal emissions as well as track eruptive activity that may impact provided in collaboration with multiple space agencies. populations and infrastructure on the ground and in the Within the pilot framework, we present preliminary InSAR results at Llaima, Villarrica and Calbuco volcanoes, all of air, ultimately leading to improved targeting for which had recent unrest, but none of which had a simple permanent satellite-based observations and in-situ relation between eruption and ground deformation volcanic monitoring efforts. because they lacked either pre-eruptive uplift and coeruptive subsidence or both. Among the different types of available satellite data made available by the collaboration of the pilot project Keywords: InSAR, volcano geodesy, Llaima volcano, and different space agencies, we focus in this work on Villarrica volcano, Calbuco volcano. new InSAR (interferometric synthetic aperture radar) observations (e.g., Dzurisin and Lu, 2007; Simons and Rosen, 2007; Lu and Dzurisin, 2015; Pinel et al., 2015) at 1 Introduction Llaima, Villarrica, and Calbuco volcanoes, all of which erupted in the past ten years and are classified as the Satellite observations are a cost effective tool for most dangerous in Chile due to their closeness to monitoring large numbers of volcanoes in areas with inhabitated areas. Although there is a global general scarce instrumentation or difficult access. In the context association between deformation and eruption (Biggs et of the 2012 Santorini Report on Satellite Earth al., 2014), deformation sequences associated with Observation and Geohazards, CEOS (Committee on eruption at particular volcanoes are diverse and complex Earth Observation Satellites) has developed a pilot (Fournier et al., 2010; Ebmeier et al., 2013). We show project to showcase remote sensing for volcano hazard that none of the eruptions at Llaima, Villarica or Calbuco mitigation and response. Specifically, the pilot aims to were accompanied by a simple deformation pattern of pre demonstrate the feasibility of global volcano monitoring eruptive uplift followed by coeruptive subsidence or of Holocene volcanoes by undertaking regional both, in contrast with simple theoretical models of the monitoring of volcanic arcs in Latin America, using eruptive cycle which show that a volcano should uplift satellite earth observations data to track deformation as before and subside after an eruption (e.g., Lu et al., well as gas, ash, and thermal emissions. Latin America 2003). All of these results have been shared with to was chosen because the volcanoes are situated in a OVDAS (Southern Andes Volcano Observatory), which diversity of environments, providing a good test of the has used them in their hazard interpretation. capabilities of different types of satellite data under different conditions; volcanic activity is abundant, and 27 ST 11 TERREMOTOS, VOLCANES Y OTROS PELIGROS GEOLÓGICOS

2 InSAR data processing both PALSAR time series before the April 3rd 2009 The CEOS pilot project, satellite volcano monitoring in eruption, above the 4 cm uncertainty for steep Latin America and new InSAR ground deformation results We use nearly all available data acquired by the stratovolcanoes (Ebmeier et al., 2013b) interpreted as pre international spacebourne SAR constellation that spans eruptive magma intrusion. The inversion for a at Llaima, Villarrica and Calbuco volcanoes the different eruptions since 2006 at the three studied subhorizontal sill indicates depths of 5.3 km beneath the volcanoes. The data includes the C band (5.6 cm volcano base in agreement with petrological evidence of wavelength) platforms ENVISAT ASAR (2006-2012), shallow magma storage (Bouvet de Maisonneuve et al., 2012). Francisco Delgado*, Matthew E. Pritchard RADARSAT-2 (RS2 hereafter) (2012-2015) and Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA Sentinel-1 (2015); the X band (3.1 cm) TerraSAR-X Susanna Ebmeier, Juliet Biggs, David Arnold (TSX) and COSMO-SkyMed (CSK) (2011-2015), and L 3.2 Villarrica volcano School of Earth Sciences, University of Bristol, Bristol, UK band (23.6 cm) ALOS PALSAR data (2007-2011). We nd Pablo González note that the data coverage is uneven at these volcanoes. Villarrica volcano erupted on March 3 2015 in a small School of Earth and Environment, University of Leeds, Leeds, UK For example, the ASAR data density is much lower at strombolian eruption (VEI 1-2), after a few days with Michael Poland Calbuco than at either Villarrica or Llaima and, neither increased seismicity elevated above background levels. Cascades Volcano Observatory, United States Geological Survey (USGS), Vancouver, Washington, USA CSK and TSX acquired data suitable for standard CSK pre, co and post eruptive interferograms show both Simona Zoffoli stripmap interferometry at Calbuco before the 2015 positive and negative range change signals of variable Agenzia Spaziale Italiana (ASI), Rome, Italy. eruption. Interferograms were processed with the amplitude (Figure 1). The lack of other elevated areas in Loreto Córdova, Luis E. Lara Caltech/JPL ROI_PAC (Rosen et al., 2004) and ISCE the small CSK swaths complicates the interpretation of Observatorio Volcanológico de los Ands del Sur (OVDAS), SERNAGEOMIN, Temuco, Chile softwares while Sentinel-1 data were processed with the whether these signals are topographically correlated

GAMMA software. The topographic phase was removed phase delays of likely atmospheric origin or not. In the *Contact email: [email protected] absence of other independent data, we modeled the with the 3 arcsec Shuttle Radar Topographic Mission monitoring agencies in Latin American countries would signals using a Mogi directly benefit from the resources that this pilot will (SRTM) digital elevation model, except for the CSK data which was processed with the 1 arcsec SRTM. We use a COSMO−SkyMed, 15/03/31−15/02/11 COSMO−SkyMed, 15/04/12−15/02/11 Abstract. We present results from the 3-year CEOS Bperp 195 m Bperp 32 m volcano pilot project, which aims to monitor all Latin modification of the SBAS time series method (e.g., America 315 Holocene volcanoes at least 4 times/year make available. It is hoped that the regional study will Berardino et al., 2002; Henderson and Pritchard, 2013) to and the ~50 erupting or deforming volcanoes at least demonstrate that Earth observation data can help to retrieve the ground deformation time evolution only for monthly. The pilot will incorporate satellite observations to identify volcanoes that may become active in the future the L band PALSAR data because there is more data track deformation, gas, ash, and thermal emissions as well as track eruptive activity that may impact available (because of the higher signal coherence) with provided in collaboration with multiple space agencies. populations and infrastructure on the ground and in the this sensor than the C or X band satellites. When Within the pilot framework, we present preliminary InSAR observed, deformation signals were downsampled results at Llaima, Villarrica and Calbuco volcanoes, all of air, ultimately leading to improved targeting for permanent satellite-based observations and in-situ (Lohman and Simons, 2005) and jointly inverted with the which had recent unrest, but none of which had a simple non-linear neighbourhood algorithm (Sambridge, 1998) relation between eruption and ground deformation volcanic monitoring efforts. COSMO−SkyMed, 15/03/11−15/02/11 COSMO−SkyMed, 15/03/27−15/02/19 using standard formulas for the surface displacements 39.2˚S Bperp 120 m Bperp −189 m because they lacked either pre-eruptive uplift and co- produced by a subhorizontal tensile dislocation (Okada, eruptive subsidence or both. Among the different types of available satellite data 1985) and a small pressurized sphere (Mogi, 1958) made available by the collaboration of the pilot project cm Keywords: InSAR, volcano geodesy, Llaima volcano, and different space agencies, we focus in this work on embedded in a linear elastic halfspace. 5 Villarrica volcano, Calbuco volcano. new InSAR (interferometric synthetic aperture radar) 39.4˚S 0

observations (e.g., Dzurisin and Lu, 2007; Simons and −5 Rosen, 2007; Lu and Dzurisin, 2015; Pinel et al., 2015) at 3 InSAR results 1 Introduction Llaima, Villarrica, and Calbuco volcanoes, all of which 10 km 29 erupted in the past ten years and are classified as the 3.1 Llaima volcano 39.6˚S Satellite observations are a cost effective tool for most dangerous in Chile due to their closeness to 72.2˚W 72˚W 71.8˚W monitoring large numbers of volcanoes in areas with inhabitated areas. Although there is a global general Llaima volcano underwent a complex eruptive cycle Figure 1. Villarrica volcano coeruptive interferograms scarce instrumentation or difficult access. In the context association between deformation and eruption (Biggs et between May 2007 and July 2009, with the largest of the 2012 Santorini Report on Satellite Earth st rd showing ground displacement in the radar Line-Of-Sight from al., 2014), deformation sequences associated with eruption on January 1 2008 and April 3 2009 (Moreno CSK. The dates of the interferograms are shown in each image Observation and Geohazards, CEOS (Committee on eruption at particular volcanoes are diverse and complex et al., 2009). Multitrack PALSAR time series show and Bperp is the perpendicular baseline between the satellite Earth Observation Satellites) has developed a pilot (Fournier et al., 2010; Ebmeier et al., 2013). We show subsidence signals at rates of -1 to -1.5 cm/yr between overflights. We suspect that most of the signals in these project to showcase remote sensing for volcano hazard that none of the eruptions at Llaima, Villarica or Calbuco 2007 and 2011, that we think are an artifact of changes in interferograms (except the uplift signal observed at the SE of mitigation and response. Specifically, the pilot aims to were accompanied by a simple deformation pattern of pre the atmosphere as it is below the ˜2.5 cm/yr uncertainty the volcano in the 15/04/12-15/02/11 interferogram) are caused demonstrate the feasibility of global volcano monitoring eruptive uplift followed by coeruptive subsidence or of the PALSAR time series (Ebmeier et al., 2013; by atmospheric changes and not real ground deformation, but of Holocene volcanoes by undertaking regional both, in contrast with simple theoretical models of the Philibosian and Simons, 2010; Remy et al., 2015). On the further work will clarify this. monitoring of volcanic arcs in Latin America, using eruptive cycle which show that a volcano should uplift other hand, ASAR interferograms that span the January satellite earth observations data to track deformation as before and subside after an eruption (e.g., Lu et al., 1st 2008 eruption show signals that have been interpreted source that takes into account the volcano topography well as gas, ash, and thermal emissions. Latin America 2003). All of these results have been shared with to as ground uplift (Bathke et al., 2011). As the different (Williams and Wadge, 1998) and inverted each was chosen because the volcanoes are situated in a OVDAS (Southern Andes Volcano Observatory), which data sets show opposite results, all the observed signals interferogram for a linear ramp to account for long diversity of environments, providing a good test of the has used them in their hazard interpretation. are likely produced by variations in the tropospheric wavelength errors, volume change (source strength) and capabilities of different types of satellite data under precipitable water vapor (PWV) content (Remy et al., a simple linear function that takes into account the different conditions; volcanic activity is abundant, and 2015). On the other hand, a burst of uplift is imaged by correlation of phase and topography frequently observed 28 AT 4 Impacto de las GeocIencIas en la socIedad

at steep stratovolcanoes (Beauducel et al., 1999). Then, ˜0.045 km3, in agreement with recordings from a tilt we retrieved the source volumetric change time evolution meter located 4 km W of the volcano. This model will be by means of standard linear least squares. Although the refined with additional descending interferograms that simplistic model can not account for all the observed help recover more than one component of the ground signals, as systematic residuals are observed, the model deformation signal. can predict most of the observed signals. The volume change time series shows no systematic pattern before 4 Discussion and conclusion and after the eruption. Therefore, the observed volcano fringes are produced by PWV changes and no ground We note that there are multiple explanations for the lack deformation signal was unambiguously observed from of ground deformation at these volcanoes. At persistently this data set. We note that the phase delays are strong at degassing volcanoes like Villarrica and Llaima, magma this volcano and can introduce signals that resemble the chamber pressurization may be relieved by permanent topography with amplitudes up to 3.5 cm per km of degassing reflecting the presence of a permanent or semi elevation. permanent open conduit (e.g. examples from Chaussard et al., 2013; Ebmeier et al., 2013; Geirsson et al., 2014). 3.3 Calbuco volcano At such systems minor explosions could be associated with conduit pressurization changes, which may result in Calbuco volcano erupted on April 22nd 2015 with little deformation only near the volcano summit where InSAR previous unrest in a large subplinian eruption (VEI 4). data tends to be systematically decorrelated by geometric PALSAR (2007/02-2011/02) and ASAR (2010/10- distortions inherent to spacebourne SAR systems (e.g., 2012/03) stacks and individual RS2 (2012-2015) and Zebker et al., 2000; Pinel et al., 2014). On the other hand, Sentinel-1 (2015) interferograms do not show clear Llaima ground uplift before the April 3rd 2009 eruption evidence of pre eruptive ground up to 1 and a half days can be explained as the volcano changed its behavior to a before the eruption. On the other hand, coeruptive closed system with a sealed conduit, were chamber ascending Sentinel-1 interferograms (Figure 2) show a pressurization caused the edifice to uplift. This is deflation signal with a maximum line of sight amplitude supported by airborne observations that showed that pyroclastic material obstructed the eruptive vents before Residual this eruption (OVDAS, 2009). We also note that large data gaps exists between PALSAR acquisitions, as Llaima might have uplifted and subsided during a single

cm 46 days orbital cycle, thus rendering the time series 2 aliased. 0

−2 The lack of pre eruptive deformation at Calbuco is more difficult to explain given the eruption size and could be Sentinel−1a interferogram, 15/04/26 − 15/04/14 Mogi synthetic related to fast ascent of highly compressible gas-rich 41.1˚S magmas without leaving a geodetic signal in the available InSAR data (Biggs et al., 2014), as in Chaitén cm volcano (e.g., Fournier et al., 2010; Wicks et al., 2011). 41.4˚S 0 −6 −12 33 The growing density of SAR acquisitions with the new 20 km constellations such as CSK, Sentinel-1 and ALOS-2 will help to better understand the relation between ground 73.2˚W 72.9˚W 72.6˚W 72.3˚W deformation and eruption, improving existing models of Figure 2. Calbuco volcano coeruptive interferogram from the the eruptive cycle, and to extend the use of satellite data Sentinel stallite (date at the top of the left image), model in hazard assessment. prediction (center) and residual (right). Blue triangles are volcanoes and the red point is the location of the deflating Mogi source. The model parameters are described in the text. Acknowledgements

of 12 cm located in the W part of the volcano. This signal The volcano pilot project is possible thanks to the CEOS is absent in 1 day coeruptive descending CSK coordination of various space agencies (ESA, ASI, CSA, interferograms which indicates that the subsidence was DLR, JAXA, NASA, CNES) and the management by fast and occurred during the first eruption day. The USGS and ASI. F.D. acknowledges CONICYT-Becas deflation signal can be modeled by a small pressurized Chile for a Ph.D. grant. sphere to retrieve the inferred magma chamber position and volume change. The inversion results show that the source is located 5 km SW of the volcano at a depth of References 9.3 km beneath the surface, with volume changes of 29 ST 11 TERREMOTOS, VOLCANES Y OTROS PELIGROS GEOLÓGICOS

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