Applications: Volcanoes (1)

At dome building volcanoes, the explosive excavation of the crater and the first days of new dome growth are one of the most dynamic morphometric changes that may occur. Associated with initial
explosions, the pathways for new magma rising are developing. The excavated vent and crater morphology, in turn, itself are controlling the later development of a dome building stage. Consequently, as we herein show, the observation of this early explosion and dome growth episode is the key for understanding the imminent eruption dynamics.
This paper describes the destructive-constructive activity at Merapi and at Colima volcano, as occurred in 2012-2013. The crater geometry and early dome formation was observed by combination of spotlight TerraSAR-X satellite images and fixed time-lapse cameras located at several kilometers distance. This imagery allowed identifying precursory activity, sequential explosion and crater excavation stages, followed by dome growth. By means of particle image velocimetry, the digital flow field is computed from consecutive camera images, showing that vertical dome growth dominates at the beginning. This is interrupted by gravitationally spreading of the dome, and grading into a later flow domain. The comparison of these imaging data therefore allows exploring the dynamic growth and instabilities of the summit region of a dome building volcano. This study allows a detailed view into the explosive crater formation and new dome formation.

Estimating the amount of erupted material during a volcanic crisis is one of the major challenges in volcano research. One way to do this and to discriminate between juvenile and non-juvenile fraction is to assess topographic changes before and after an eruption while using area-wide 3D data. An innovative way to acquire 3D information of volcanic test sites repeatedly is using data of the German TanDEM-X satellite mission. TanDEM-X consists of the two nearly identical radar satellites TerraSAR-X and TanDEM-X that fly in a close helical formation, building a large single-pass SAR interferometer with adaptable across-track baselines. The short repeat-interval of 11 days allows generating digital elevation models (DEMs) of the area of investigation every 11 days, or multiples of this. Differencing DEMs acquired prior, during, or after a volcanic crisis results in the topographic and volumetric changes due to the volcanic activity.

For testing the TanDEM-X data to measure topographic and volumetric changes, we chose three different test sites characterized by different patterns of volcanic activity that caused a topographic change.

(1)    As first test site, we chose Merapi in Indonesia and analyzed the topographic loss in the summit area due to the 2010 eruption. Merapi is a dome-building volcano with varying activity. During the hazardous eruption of October/November 2010, the old lava dome collapsed, a new lava dome was extruded and collapsed again within twelve days. We show three DEMs derived from bistatic TanDEM-X InSAR in descending orbit taken before and after the eruption. The preliminary estimated volumetric loss of 19 X 10⁶ m³ in the summit area is reasonable; however, strong phase noise due to geometrical decorrelation and resulting unwrapping errors affect the result.

(2)    Volcán de Colima in Mexico is – as is Merapi – a dome-building volcano with varying activity. Here, we show our results from a small explosive event that happened in June 2011. Unlike Merapi whose eruption led to a topographic change of about 200 m, the explosion at Volcán de Colima led to a topographic change of only 20 m. The study therefore enabled us to evaluate the capacities and limitations of the bistatic TanDEM-X data to measure small topographic changes at active dome-building volcanoes. At Colima, we analyzed six bistatic data pairs. Two of them were recorded prior to the explosion, the other four data pairs were recorded after the explosion. A comparison of the TanDEM-X based results to photogrammetric DEMs acquired by James & Varley (2012) enabled to validate the presented method to measure topographic changes at active volcanoes using TanDEM-X.

(3)    The third test site – Tolbachik in Kamchatka – is entirely different than Merapi and Volcán de Colima. The Tolbachik massif in Kamchatka is composed of two overlapping, but morphologically dissimilar volcanoes. Whereas Plosky Tolbachik in the east is a basaltic shieldvolcano, Ostry Tolbachik in the west is the higher sharped topped stratovolcano. After more than 35 years of quiescence, Tolbachik started erupting in November 2012 for about nine month until the end of August, 2013. The eruption was composed of very fluid lava flows that effused along a northeast-southwest trending fissure to the south of Ostry and Plosky Tolbachik. We analyzed two DEMs – one from data acquired prior to the volcanic activity and the other one acquired after the fissure had stopped erupting. The results proof that topographic changes due to lava flow activity are also measureable solely using double differential TanDEM-X InSAR.

We apply double differential TanDEM-X InSAR to measure topographic changes due to volcanic activity.We show that using InSAR alone it is possible to quantitatively assess large mass movements produced during the rapidly changing morphologies of volcanoes during eruptions. The three different case studies prove that various volcanic features are measureable using TanDEM-X. They also demonstrate the limitations of the method imposed by geometrical effects in topographically rough areas.

Reference:

James, M.R. and Varley, N. (2012): Identification of structural controls in an active lava dome with high resolution DEMs: Volcán de Colima, Mexico. Geophysical Research Letters, 39:L22303.

With its global coverage and all-weather imaging capability, interferometric synthetic aperture radar (InSAR) has become an increasingly important technique for studying magma dynamics at volcanoes in remote regions, such as the Aleutian Islands. The spatial distribution of surface deformation derived from InSAR data enables the construction of detailed mechanical models to enhance the study of magmatic processes. To study Aleutian volcanism, we processed nearly 12,000 SAR images acquired by ERS-1, JERS-1, ERS-2, Radarsat-1, Envisat, ALOS, and TerraSAR-X from the early 1990s to 2010. We combined these SAR images to produce about 25,000 interferograms, which we analyzed for evidence of surface deformation at most of the arc’s Holocene volcanoes. Where surface displacements were sufficiently strong, we used analytical models to estimate the location, shape, and volume change of deformation sources [Lu and Dzurisin, 2014].

This paper summarizes deformation processes at Aleutian volcanoes observed with InSAR, including: (1) time-variant volcanic inflation and magmatic intrusion, (2) deformation preceding and accompanying seismic swarms , (3) persistent volcano-wide subsidence at calderas that last erupted tens of years ago, (4) episodic magma intrusion and associated tectonic stress release, (5) subsidence caused by a decrease in pore fluid pressure in active hydrothermal systems, (6) subsidence of surface lava and pyroclastic flows, and (7) a lack of deformation at some volcanoes with recent eruptions, where deformation might be expected. Among the inferred mechanisms are magma accumulation in and withdrawal from crustal magma reservoirs, pressurization/depressurization of hydrothermal systems,  and thermo-elastic contraction of young lava flows. Our work demonstrates that deformation patterns and associated magma supply mechanisms at Aleutian volcanoes are diverse and vary in both space and time. By combining InSAR results with information from the geologic record, accounts of historical eruptions, and data from seismology, petrology, gas geochemistry, and other sources, we have developed conceptual models for the magma plumbing systems and behaviors of many volcanoes in the Aleutian arc. We realize that these models are simplistic, but it is our hope that they will serve as foundations that will be refined as additional information becomes available. Finally, we have compared our InSAR observations from the Aleutians with those from the Andes and Indonesia to highlight the similarities and differences in volcanism between volcanic arcs [Lu and Dzurisin, 2014].

Lu, Z., and Dzurisin, D., 2014. “InSAR Imaging of Aleutian Volcanoes: Monitoring a Volcanic Arc from Space”: Springer Praxis Books, Geophysical Sciences, ISBN 978-3-642-00347-9, Springer, 390 pp.

We report on the rapidly evolving volcano unrest centered south of Chiles and Cerro Negro volcanoes along the Ecuador-Colombia border in the northern Andes. The Chiles and Cerro Negro volcanoes have no historical record of eruptive activity, with most recent large eruptions occurring many thousands of years ago. Anomalous seismicity started in late 2013 with a significant increase from March 2014 through June, followed by a slow-down in July and August. Starting on September 27, 2014, a rapid increase in seismicity, resulting in over 100,000 events in less than a month, marked a dramatic escalation of the volcano unrest. From late March through late June 2014 synthetic aperture radar (SAR) data from the Italian Space Agency (ASI) COSMO-SkyMed (CSK) constellation of satellites were acquired in the initial volcano unrest response. However, following the slow-down in seismicity rates, the CSK acquisitions were allowed to lapse. On October 20, 2014, an M5.8 earthquake sparked renewed SAR data acquisitions from CSK and the German Aerospace Center (DLR) TerraSAR-X (TSX) satellite. Since the changes were observed in volcanic activity, both monitoring and care of the crisis has been managed jointly by the Colombian Geological Service and the Geophysical Institute (IG) of Ecuador. The initial CSK interferogram was used by IG personnel to guide installation of new instrumentation and for VDAP personnel to direct remote sending observations looking for surface expressions of fracturing and possible emissions.

In late October CSK and TSX acquisitions resumed along with other satellites to the extent possible (including RADARSAT-2 and ALOS-2). As of the writing of this abstract only CSK data have shown significant deformation, with significant differences between the descending and ascending track deformation patterns. This is in contrast to the CSK time series from late march through June that showed no discernable deformation. In-situ data, including electronic tilt and GPS continuous measurements show differing signals, with the tilt apparently showing steady deformation at Chiles, whereas the GPS is relatively flat since early 2014, possibly consistent with the InSAR, with an abrupt increase in horizontal displacements starting in September, commensurate with the seismicity increase. A TSX interferogram from May to October 18, 2014, reveals no deformation either, suggesting the observed fringes in the CSK data may be largely due to the M5.8 earthquake. More recent TSX data will be soon forthcoming and will add to the information gained so far.

CSK descending and ascending track interferograms show significantly different deformation signatures, with the ascending one displaying considerably greater complexity. Our most recent CSK descending data (October 31 – October 24) - following the M5.8 earthquake - shows only about one fringe (1.5 cm) of deformation, which could reflect after-slip or continued fault motion if all the deformation was fault related. Therefore open questions remain regarding the sources and timing of deformation events and the contributions of seismic and magmatic sources.

We will present geodetic, seismic, and remote sensing data analysis and numerical source modeling. Source models will evolve with complexity commensurate with the observations, using inverse analytic and boundary element numerical approaches as warranted.

Since this is a rapidly evolving volcano crisis of uncertain duration and outcome and with uncertain SAR data quality and availability in the months to come, we do not know the full extent of our analysis nor can we say more regarding deeper analysis. We will also discuss future data acquisitions plans, including NASA airborne SAR acquisitions. This unrest has the potential to lead to significant eruption, but as with all unrests we cannot see into the future as of this writing. Preliminary data indicate a strongly deforming, highly seismic magmatic event that has already proven to be very interesting whatever its outcome.

Interferometric synthetic aperture radar (InSAR) is an important method for measuring surface deformation at high spatial sampling over entire volcanoes. We present the application of InSAR and in-situ data, where available, to several types of volcano deformation processes around in the Pacific Rim. We use satellite SAR using the Italian COSMO-SkyMed (CSK) X-band satellite constellation and the Canadian RADARSAT-2 C-band satellite, and the Sentinel-1 C-band satellite where possible. We have conducted airborne InSAR using the NASA UAVSAR L-band system in a significant portion of the Pacific Rim. Each of these SAR systems has advantages and disadvantages for volcano deformation science and applications. We show preliminary analysis and modeling for three specific locations, each with very particular types of activity, spatiotemporally high variability; dike intrusion and fissure eruption; detailed crater processes; and an on-going, multi-year volcano unrest: Tolbachik Volcano 2012 fissure eruption, Kamchatka; Kirishima (Shinmoe-dake) Volcano, Japan; and Copahue Volcano 2011-present inflation, Chile-Argentina border. Each of these sites presents different challenges for InSAR and shows the capabilities and limitations of InSAR for volcano science and hazard response (Figure 1).

The Tolbachik fissure eruption that started in November 2012 started during the winter when InSAR does not work in Kamchatka due to snow cover. One-year interferograms from RADARSAT-2 (descending track) and CSK (both ascending and descending tracks) satellites provide relative deformation spanning the entire dike intrusion and eruption episode. We present dike models for these data and compare them to seismic and geological observations. We use a boundary element solution that includes topography to model the finite opening dike. Preliminary modeling finds an irregular dike within the upper 3 km beneath the surface, with localized areas of greater opening (>5m) both at depth (2-3 km) and in the near surface fissure zone. Seismicity locations and timing show that magma accumulated SE of Tolbachik volcano before moving through the central conduit and propagating into the SSW trending south flank fissure system.

Shinmoe-dake volcano exhibits an irregular, smooth deformation pattern within the crater that was active during the 2011 eruption. UAVSAR 1-year interferograms show significant (multiple 12 cm fringes) deformation. Fine temporal sampling from CSK spotlight InSAR find a similar deformation pattern from both ascending and descending satellite passes. We determine that the source is very shallow (<200 m) and represents a distributed source whose process is still under investigation.

Copahue Volcano, located in the southern Andes along the Chile-Argentina border began inflating in late 2011 with the first eruptive activity starting in late December 2012. During this time interval dense InSAR time series from RADARSAT-2 and CSK descending track data reveals a nearly steady inflation of the volcano centered NNE of the active summit, extending beneath the adjacent caldera. Over the past year the addition of CSK ascending data and UAVSAR airborne interferograms provide additional constraint on the volcano source model. Preliminary models derived using a Markov Chain Monte Carlo (MCMC) Bayesian approach require a likely complex source geometry that can be represented by a shallow (~3 km) and deeper (extending to greater than 6 km) source. Trade-offs in characterizing the sources as Mogi (point), Yang (prolate spheroid), or dipping tensile dislocation, lead to similar results using different source combinations.

Finally, we will present a brief overview of UAVSAR airborne volcano observations and operations in the Pacific Rim combined with satellite SAR data (CSK, RSAT2, Sentinel-1) for monitoring select volcanoes.

 Volcanic eruptions can have high social and economic impact at local and regional scales, but relatively few volcanoes around the world are regularly monitored. Due to the large area that must be surveyed, satellite observations are often the most cost effective method of monitoring large numbers of volcanoes in areas with scarce instrumentation or difficult access. In the context of the 2012 Santorini Report on satellite Earth Observation and Geohazards, CEOS (Committee on Earth Observation Satellites) has developed a pilot project to showcase how a wide range of satellite based remote sensing platforms can produce valuable information, for use by organizations responsible for volcano hazard assessment, mitigation and response, to improve disaster risk management (DRM). The first component of the pilot aims to demonstrate the feasibility of global volcano monitoring of Holocene volcanoes by undertaking regional monitoring of volcanic arcs in Latin America using earth observations data to track ground deformation, in addition to gas, ash, and thermal emissions.

Latin America was chosen for the regional component of the pilot because the volcanoes are located in a wide range of environments, from tropical rainforest through to high altitude desert. This diversity of monitoring targets provides a good test of the capabilities of satellite data in different settings. Volcanic activity is abundant including persistent eruptive activity (e.g. Tungurahua, Soufriere Hills, Arenal, Llaima) and deformation with no eruption (e.g. Uturuncu, Lazufre), and explosive eruptions have occurred frequently in the past (e.g. Cordon Caulle, Guagua Pinchincha, Pelée). Latin American volcano observatories and monitoring agencies will directly benefit from the resources this pilot will make available.

The key goals of the regional study are to demonstrate that satellite Earth observation data can help to identify volcanoes in a state of unrest that may become active in the future, as well as track eruptive activity that may impact both populations and infrastructure.  It is hoped that the pilot will ultimately lead to improved targeting for permanent satellite-based observations and in-situ volcanic monitoring efforts. The pilot project is possible thanks to data provided for free by the various space agencies (ESA, CSA, ASI, DLR, JAXA, NASA, CNES).

Here, we focus on preliminary ground deformation results using SAR satellites for selected areas in the Northern and Southern Andes, Central America, and the Caribbean with recent unrest. Preliminary results have been obtained for Cordon Caulle (Chile), Tungurahua, Cotopaxi and Reventador (Ecuador), Soufrière Hills Volcano (Montserrat), Masaya (Nicaragua) and from the recent unrest episode at Cerro Negro/Chiles (Ecuador-Colombia border), and will be presented here.