Volcanic Deformation Research Articles

GIS기법을 이용한 백두산 화산재해 종합평가 연구

2014년 에콰도르의 툰구라와 화산폭발, 2010년 아이슬란드 에이야프야틀라이외쿠틀 화산폭발 등과 같이 최근 화산활동으로 인한 재해피해가 증가하고 있으며 이에 대한 대책마련이 시급한 실정이다. 본 연구에서는 현재 폭발 위험성이 높은 활화산 중 하나인 백두산을 대상으로 객관적 관측자료와 과학적인 방법에 근거하여 재해위험지역 분석을 실시하였다. 첫 번째로 중국학자 Liu Ruoxin의 연구에 근거하여 1215(<TEX>${\pm}15$</TEX>)년 백두산 화산 대폭발 화산재해 데이터를 참조하여 백두산지역의 지진관측자료와 화산지역 형태변화 관측자료, 화산지역 유체지구화학관측자료, 사회경제 통계데이터를 이용해 재해유발요소, 잠재적인 재해유발환경, 피해대상의 취약성을 종합적으로 평가하였다. 평가결과를 토대로 대상지역에 대한 백두산화산재해위험등급분포도를 산출하였으며, 그 결과 백두산화산재해위험등급을 4단계로 체계화하였다. 분석결과 백두산화산재해위험등급은 중심부에서 주변으로 갈수록 점차 등급이 낮아지는 것으로 분석되었으며 1,2급 위험지역은 화산폭발 시 위험도와 피해가 클 것으로 예상되는 고위험지역으로, 3,4급 위험 지역은 화산재해위험이 상대적으로 낮은 지역으로 나타났다. 또한 같은 강도의 화산재해요소의 작용하에서는 연구지역의 서쪽지역이 받는 위험성이 동쪽지역보다 높은데 이는 비교적 낮은 잠재적인 재해유발환경의 안정성과 높은 피해대상 취약성에 의해 결정됨을 확인할 수 있었다. Recently there are many disasters caused by volcanic activities such as the eruptions in Tungurahua, Ecuador(2014) and <TEX>$Eyjafjallaj\ddot{o}kull$</TEX>, Iceland(2010). Therefore, it is required to prepare countermeasures for the disasters. This study analyzes the Baekdu Mountain area, where is the risky area because it is active volcano, based on the observed data and scientific methods in order to assess a risk, produce a hazard map and analyze a degree of risk caused by the volcano. Firstly, it is reviewed for the research about the Baekdu mountain volcanic eruption in 1215(<TEX>${\pm}15$</TEX> years) done by Liu Ruoxin. And the factors causing volcanic disaster, environmental effects, and vulnerability of Baekdu Mountain are assessed by the dataset, which includes the earthquake monitoring data, the volcanic deformation monitoring data, the volcanic fluid geochemical monitoring data, and the socio-economic statistics data. A hazard, especially caused by a volcano, distribution map for the Baekdu Mountain Area is produced by using the assessment results, and the map is used to establish the disaster risk index system which has the four phases. The first and second phases are very high risky area when the Baekdu Mountain erupts, and the third and fourth phases are less dangerous area. The map shows that the center of mountain has the first phase and the farther area from the center has the lower phase. Also, the western of Baekdu Mountain is more vulnerable to get the risk than the eastern when the factors causing volcanic disasters are equally applied. It seems to be caused by the lower stability of the environment and the higher vulnerability.

Plate boundary deformation in North Iceland during 1992–2009 revealed by InSAR time-series analysis and GPS

In North Iceland, extensional plate motion is accommodated by the Northern Volcanic Zone, a set of en-echelon volcanic systems, and the Tjörnes Fracture Zone, a transform offset in the mid-Atlantic Ridge consisting of two parallel transform lineaments. The southern lineament, the Húsavík–Flatey fault, is a 100km-long right-lateral strike slip fault that has not ruptured for more than 140years and poses a significant seismic hazard to Húsavík, a fishing town located by the fault, and to other coastal communities. We present results of InSAR time-series analysis data spanning almost two decades (1992–2009) that show extensional and interseismic deformation within the Northern Volcanic Zone and the on-shore part of the Tjörnes Fracture Zone. The results also exhibit transient inflation at Theistareykir volcano, deflation at Krafla central volcano and a broad uplift north of Krafla. The current plate extension is not uniform across the Northern Volcanic Zone, but concentrated at the western fissures of the Theistareykir volcanic system and the outermost fissures of the Krafla fissure swarm. We combine a back-slip plate boundary model with a set of point pressure sources representing volcanic changes to describe the current extensional plate boundary deformation and update the previous estimations of the locking depth and slip rate of the Húsavík–Flatey fault that were based on GPS data alone. Using different combinations of input data, we find that the Húsavík–Flatey fault has a locking depth of 6–10km and, with a slip rate of 6–9mm/yr, is accommodating about a third of the full transform motion. We furthermore show that while the InSAR data provide important constraints on the volcanic deformation within the NVZ, they do not significantly improve the model parameter estimation for the HFF, as the dense GPS network appears to better capture the deformation across the fault.

Benchmarking and developing numerical Finite Element models of volcanic deformation

Volcanic deformation during an unrest episode can provide valuable insights into potential magmatic plumbing system dynamics. Paramount to this is a model linking the recorded ground movement to the causative source at depth. Most models employ analytical techniques due to their simplicity, but these are limited in their approach due to a number of necessary assumptions, and restricted to crude subsurface representations. We address this problem by providing guidelines and example model files to benchmark against a simple, analytical model with a numerical Finite Element approach using COMSOL Multiphysics. The boundary conditions should also be applicable to other Finite Element modeling packages. Then, due to the flexibility of the Finite Element method, this allows a progression of adding increasing complexities to reproduce the likely intricacies of the subsurface. We thus provide further guidelines and accompanying model files to incorporate subsurface heterogeneity, benchmarked viscoelastic rheology and temperature-dependent mechanics. In doing so, we highlight that setting up more integrated geodetic models is not particularly difficult and can alter inferred source characteristics and dynamics. The models are applied to Uturuncu volcano in southern Bolivia to demonstrate the approach.

Correction of Atmospheric Phase Screen in Time Series InSAR Using WRF Model for Monitoring Volcanic Activities

One of the main limitations in measuring ground deformation using synthetic aperture radar interferometry (InSAR) is atmospheric phase delay effects. In volcanic regions, the atmospheric phase delay effects can cause serious problems in detecting volcanic unrest because atmospheric thickness is inversely related with the elevation of a volcanic mountain. It is commonly known that the atmospheric phase screen (APS) can be decomposed spatially into stratified and turbulent components. In this paper, the stratified and turbulent atmospheric conditions of a volcanic area were simulated using weather research and forecasting (WRF) model, and the simulated atmospheric conditions were compared with in situ radiosonde data. The comparison results proved that the stratified APS from the WRF model could reflect the reasonable patterns of seasonal changes and vertical profiles with dependable quality. We also found that the stratified APS was significantly correlated with time and sometimes severely contaminated the quality of volcanic deformation estimation. These results indicate that the temporal high-pass (HP) filtering, which has been usually applied in time series InSAR analysis for extracting and removing APS, cannot work properly in volcanic area. Thus, we propose a new method that employs the stratified APS obtained from the WRF model by correlating with topography and the (residual) turbulent APS that can be effectively eliminated by temporal HP filtering in persistent scatterer interferometry (PSI). We applied the proposed method (atmosphere-corrected PSI) to Advanced Land Observing Satellite Phased Array type L-band SAR data that cover Shinmoedake volcano, Japan, and found that the estimated surface deformation and APS agreed well with those measured from GPS and Moderate-Resolution Imaging Spectroradiometer data, respectively.

Efficient inversion of three-dimensional finite element models of volcano deformation

Numerical techniques, as such as finite element method, allow for the inclusion of features, such as topography and/or mechanical heterogeneities, for the interpretation of volcanic deformation. However, models based on these numerical techniques usually are not suitable to be included in non-linear estimations of source parameters based on explorative optimization schemes because they require a calculation of the numerical approach for every evaluation of the misfit function. We present a procedure for finite element (FE) models that can be combined with explorative inversion schemes. The methodology is based on including a body force term representing an infinitesimal source in the model formulation that is responsible for pressure (volume) changes in the medium. This provides significant savings in both the time required for mesh generation and actual computational time of the numerical approach. Furthermore, we develop an inversion algorithm to estimate those parameters that characterize the changes in location and pressure (volume) of deformation sources. Both provide FE inversions in a single step, avoiding remeshing and assembly of the linear system of algebraic equations that define the numerical approach and/or the automatic mesh generation. After providing the theoretical basis for the model, the numerical approach and the algorithm for the inversions, we test the methodology using a synthetic example in a stratovolcano. Our results suggest that the FE inversion methodology can be considered suitable for efficiently save time in quantitative interpretations of volcano deformation.

Volcano inflation prior to an eruption: Numerical simulations based on a 1-D magma flow model in an open conduit

We numerically simulate volcanic inflation caused by magma ascent in a shallow conduit at volcanoes which repeatedly erupt, in order to understand the effect of volatile behavior on magma from geodetic data. Considering magma in which the relative velocities between melt and gas bubbles are negligible, we model magma flow in a one-dimensional open conduit with diffusive gas bubble growth. We calculate the ground displacements and tilts caused by spatio-temporal changes of magma pressure in the conduit. Our simulations show that magma without volatiles causes decelerated changes in volcanic inflation. Magma with gas bubble growth inflates the volcano with a constant, or accelerated, rate. Temporal changes of volcanic deformation are also affected by the magma pressure at the bottom of the conduit. When the pressure is small, the displacements and tilts increase in proportion to the 1.5th power of time. This time rate is similar to that predicted from a basic gas bubble growth model. When the pressure equals the lithostatic pressure, the effects of gas bubble growth relatively decrease and the displacements and tilts increase linearly with time.

Decadal volcanic deformation in the Central Andes Volcanic Zone revealed by InSAR time series

Decadal trends of volcanic deformation in the Central Andes Volcanic Zone (CVZ) are identified with Interferometric Synthetic Aperture Radar (InSAR) stacks and time series velocity maps covering an area 19°S–27°S and 66°W–69°W. We combine over 750 ERS and Envisat interferograms from two descending and three ascending tracks. These tracks cover 100,000 km 2 and span 1992–2011. Our analysis extends observations at Cerro Blanco, Uturuncu, and Lazufre volcanic centers and uncovers two previously undocumented deformation centers: Cerro Overo in Northern Chile and Putana Volcano in Southwest Bolivia. Cerro Overo exhibits a transition from steady −0.4 cm/yr deflation to 0.5 cm/yr inflation over several years. Putana Volcano underwent a short‐lived episode of uplift between 13 September 2009 and 31 January 2010, with a maximum uplift of 4.0 cm. Cerro Blanco continues −1.0 cm/yr deflation since 1995. Uplift at Lazufre began between 1997 and 2000 and has gradually accelerated to 3.5 cm/yr since 2005. Uturuncu volcano continues 1.0 cm/yr monotonic uplift since 1992 and shows evidence for a broad moat of subsidence surrounding the uplifting region. Four of the nine deformation events in the CVZ are not obviously associated with a particular volcanic edifice. Furthermore, there is significant spatial and temporal variability of these deformation events within a small geographic area.

Radar interferometry techniques for the study of ground subsidence phenomena: a review of practical issues through cases in Spain

Subsidence related to multiple natural and human-induced processes affects an increasing number of areas worldwide. Although this phenomenon may involve surface deformation with 3D displacement components, negative vertical movement, either progressive or episodic, tends to dominate. Over the last decades, differential SAR interferometry (DInSAR) has become a very useful remote sensing tool for accurately measuring the spatial and temporal evolution of surface displacements over broad areas. This work discusses the main advantages and limitations of addressing active subsidence phenomena by means of DInSAR techniques from an end-user point of view. Special attention is paid to the spatial and temporal resolution, the precision of the measurements, and the usefulness of the data. The presented analysis is focused on DInSAR results exploitation of various ground subsidence phenomena (groundwater withdrawal, soil compaction, mining subsidence, evaporite dissolution subsidence, and volcanic deformation) with different displacement patterns in a selection of subsidence areas in Spain. Finally, a cost comparative study is performed for the different techniques applied.

The Mechanisms of Earthquakes and Faulting in the Southern Gulf of California

Abstract Accurate earthquake locations and their focal mechanisms can illuminate the distribution and mode of deformation at rifted continental margins. The Pacific–North America (Pa–NA) plate boundary within the Gulf of California (GoC) provides an excellent opportunity to explore the evolution and kinematics of rifting, as continental extension in the north transitions to seafloor spreading in the south. From October 2005 to October 2006, an array of eight four‐component ocean‐bottom seismographs deployed in the GoC recorded seismicity as part of the Sea of Cortez Ocean‐Bottom Array (SCOOBA) experiment. By combining the data with those from the onshore Network of Autonomously Recording Seismographs (NARS)‐Baja array, we detect and locate ∼700 earthquakes ( M w 2.2–6.6) mainly along the northwest–southeast‐striking transform faults that delineate the plate boundary. For 36 events ( M w 3.5–6.6) with high signal‐to‐noise ratio in a long‐period (10–20 s) band, we determine deviatoric moment tensors and associated double‐couple focal mechanisms by regional waveform inversion. Many focal mechanisms are consistent with right‐lateral strike‐slip faulting along the Pa–NA transform fault system, which suggests that the transform faults primarily accommodate seismic deformation within the gulf. In addition, we capture a swarm of events on Baja California along the right‐lateral northwest–southeast‐striking Las Viboras–El Azufre fault, which may be related to ongoing geothermal activity and volcanic deformation within the peninsula. The combination of high‐resolution earthquake locations and focal mechanisms improves our understanding of the distribution of seismic deformation within the greater extensional zone in the southern GoC. Online Material: Earthquake catalog of the 695 events detected and located during our combined on‐/offshore deployment of seismometers.

Volcanic deformation and flank instability due to magmatic sources and frictional rheology: the case of Mount Etna

SUMMARY The overall picture of Mount Etna deformation emerging since a couple of decades of geodetic surveys shows effects of magma accumulation, characterized by inflation/deflation cycle, accompanied by a sliding instability of the southeast flank, whose manifestation is an increase in the horizontal deformation away from the volcano summit. This is a very interesting case to test whether advanced models, taking into account topography, internal structure and frictional rheology, may contribute to a better understanding of the complex interplay among mechanical response, magmatic activity and gravitational load occurring in a volcanic system. Using finite element numerical models we make predictions of surface displacements associated with a simple expansion source and with a dike-like vertical discontinuity. A new methodology is developed to initialize the lithostatic stress field according to the material and geometrical complexities of the models considered. Our results show that, while an amplification of the horizontal displacement can be easily obtained up to a maximum distance of 10 km from the source, we have not been able to find any configuration to extend further this signal. For the case of Mount Etna this suggests that the large horizontal displacements observed in the east flank along the coast cannot be directly related to magma accumulation below the volcano’s summit.

Reconstructing palaeo-volcanic geometries using a Geodynamic Regression Model (GRM): Application to Deception Island volcano (South Shetland Islands, Antarctica)

This article describes a reconstruction made of the palaeo-volcanic edifice on Deception Island (South Shetland Islands, Antarctica) prior to the formation of its present caldera. Deception Island is an active Quaternary volcano located in the Bransfield Strait, between the South Shetland Islands and the Antarctic Peninsula. The morphology of the island has been influenced mainly by the volcanic activity but geodynamics and volcanic deformation have also contributed. A volcanic reconstruction method, the Geodynamic Regression Model (GRM), which includes a terrain deformation factor, is proposed. In the case of Deception Island, the directions of this deformation are NW–SE and NE–SW, and match both the observed deformation of the Bransfield Strait and the volcanic deformation monitored over the last 20years in the island, using Global Navigation Satellite System (GNSS) techniques. Based on these data, possible volcanic deformation values of 5–15mm/yr in these directions have been derived. A possible coastline derived from a current bathymetry is transformed, according to values for the chosen date, to obtain the palaeo-coastline of Deception Island of 100kyears ago. Topographic, geomorphologic, volcanological and geological data in a GIS system have been considered, for computation of the outside caldera slope, palaeo-coastline, palaeo-summit height and palaeo digital elevation model (DEM). The result is a 3D palaeo-geomorphological surface model of a volcano, reaching 640m in height, with an increase of 4km3 in volume compared to the current edifice, covering 4km2 more surface area and the method reveals the previous existence of parasite volcanoes. Two photorealistic images of the island are obtained by superposition of textures extracted from a current Quick Bird satellite image also. This technique for reconstructing the terrain of an existing volcano could be useful for analysing the past and future geomorphology of this island and similar locations.

Present-day deformation in São Jorge Island, Azores, from episodic GPS measurements (2001–2011)

A network of geodetic markers for high-precision Global Positioning System (GPS) surveying was established in 2001 in the island of São Jorge, at the Azores triple junction, where the North America–Eurasia–Nubia plates meet. The aim was to monitor tectonic, volcanic, and landslide-induced surface deformation in an active tectono-volcanic region. The network consisted of 17 stations, and was occupied in 2001, 2004, and 2010. GPS observations from the three episodic campaigns were analyzed using the latest geophysical models and geodetic procedures to generate a velocity field for São Jorge Island.Surface velocities estimated at 15 inland locations reveal that São Jorge is moving neither with Eurasia nor with Nubia and presents two sectors with different behavior. The NW sector of the island is moving at a rate of 2.2±0.3mm/yr to N82°±6° while the SE sector is moving at a rate of 1.4±0.3mm/yr to N109°±11°, when compared to the velocity of Nubia predicted by ITRF2008-PMM. This velocity field cannot be explained by slip along the active faults that cross the island, nor is compatible with volcanic deformation on the active volcanic rift zones. It is suggested that the velocity differences that are measured represent deformation related to local sub-surficial magmatic/volcanic processes occurring near the island. This intra-island deformation may also be related to the stress field and seafloor spreading occurring in an area situated on the western sector of the Azores Plateau, reflecting the presence of WNW–ESE volcanic structures, along which magma intrusion produces NE–SW dilatation, bounded to the East by a NE–SW trending structure, probably of tectonic nature, working as a dextral transfer zone.

Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland

Most magmatic systems on Earth are located at actively deforming plate boundaries. In these systems, the magmatic and plate boundary deformation signals are intertwined and must be deconvolved to properly estimate magma flux and source characteristics of the magma plumbing system. We investigate the inter‐rifting and inter‐seismic deformation signals at the Eastern Volcanic Zone (EVZ) – South Iceland Seismic Zone (SISZ) ridge ‐ transform intersection and estimate the location, depth, and volume rate for magmatic sources at Hekla and Torfajökull volcanoes, which are located at the intersection. We solve simultaneously for the source parameters of the tectonic and volcanic deformation signals using a new ten‐year velocity field derived from a dense network of episodic and continuous GPS stations in south Iceland. We find the intersection of the axes of the EVZ and the SISZ is located within the Torfajökull caldera, which itself is subsiding. Deformation at Hekla is statistically best described in terms of a horizontal ellipsoidal magma chamber at 24−2+4 km depth aligned with the volcanic system and increasing in volume by 0.017−0.002+0.007 km3 per year. A spherical magma chamber centered at 24−2+5 km depth with a volume rate of 0.019−0.002+0.011 km3per year, or a vertical pipe‐shaped magma chamber between 10−1+3 km and 21−4+7 km with a volume rate of 0.008−0.001+0.003 km3 per year are also plausible models explaining the deformation at Hekla. All three models indicate magma accumulation in the lower crust or near the Moho under Hekla.

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.

IESID: Automatic system for monitoring ground deformation on the Deception Island volcano (Antarctica)

When establishing the relative distance between two GNSS–GPS stations with sub-centimeter accuracy, it is necessary to have auxiliary data, some of which can only be collected some time after the moment of measurement.However, for monitoring highly-active geodynamic areas, such as volcanoes and landslides, data precision is not as essential as rapid availability, processing of data in real-time, and fast interpretation of the results.This paper describes the development of an integrated automatic system for monitoring volcanic deformation in quasi real-time, applied to the Deception volcano (Antarctica). This experimental system integrates two independent modules that enable researchers to monitor and control the status of the GNSS–GPS stations, and to determine a surface deformation parameter. It comprises three permanent stations, one of which serves as the reference for assessing the relative distance in relation to the other two. The availability of GNSS–GPS data in quasi real-time is achieved by means of a WiFi infrastructure and automated data processing. This system provides, in quasi real-time, a time series of varying distances that tells us the extent to which any ground deformation is taking place.

Geodetic observations during the 2009 eruption of Redoubt Volcano, Alaska

In March 2009 Redoubt Volcano, about 160km to the SW of Anchorage, Alaska, began its most recent explosive eruption. Deformation induced by this event was recorded by a GPS campaign network consisting of 14 benchmarks, which had been established in 1991 after the previous eruption. The network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period. In response to precursory unrest starting in January 2009, the Alaska Volcano Observatory temporarily deployed continuously recording GPS instruments at four of the campaign benchmarks only days before the onset of explosive activity in March 2009.The only GPS instrument recording continuously during the months prior to the eruption was the Plate Boundary Observatory (PBO) station AC17, about 28km northeast of the volcano's summit. Data from this station reveals subtle motion radially outward from the volcano beginning as early as May 2008, which reversed with the onset of explosive activity.Using simple analytical models we link the precursory activity to a point source intrusion of 0.0194 0.03400.0092km3 in volume at 13.50 17.3310.17kmbelowsealevel (bsl, superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95% level). During the explosive phase about 0.05 >0.10.028km3 of magma was evacuated from a prolate spheroid with its centroid at 9.17 15.176.92kmbsl, a semimajor axis of 4.50 >10.001.25km length and a semi-minor axis of 0.475 >4.00.3km. The effusive activity is inferred to come from the same source, decreasing in volume by 0.0167 0.02280.0106km3.Including observations from seismology and petrology, we hypothesize a mid-crustal two reservoir system with material sourced from >20km flowing in at about 13.5km depth and reheating residual material in the proposed spheroid. The mixture migrated to shallower depth (2–4.5kmbsl) and reheated material there. As this residual magma erupted, it was replaced by the material from the spheroidal reservoir at 7–11.5km depth, which renders the shallow source undetectable for geodetic instruments.In addition to long term displacements we investigate sub-daily kinematic positioning solutions and find that large, short-term positioning offsets correlate with large explosive events. Spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite–station-geometry, which may be of use in volcano monitoring.

Advanced interferometric synthetic aperture radar (InSAR) time series analysis using interferograms of multiple-orbit tracks: A case study on Miyake-jima

[1] InSAR time series analysis is an effective tool for detecting spatially and temporally complicated volcanic deformation. To obtain details of such deformation, we developed an advanced InSAR time series analysis using interferograms of multiple-orbit tracks. Considering only right- (or only left-) looking SAR observations, incidence directions for different orbit tracks are mostly included in a common plane. Therefore, slant-range changes in their interferograms can be expressed by two components in the plane. This approach estimates the time series of their components from interferograms of multiple-orbit tracks by the least squares analysis, and higher accuracy is obtained if many interferograms of different orbit tracks are available. Additionally, this analysis can combine interferograms for different incidence angles. In a case study on Miyake-jima, we obtained a deformation time series corresponding to GPS observations from PALSAR interferograms of six orbit tracks. The obtained accuracy was better than that with the SBAS approach, demonstrating its effectiveness. Furthermore, it is expected that higher accuracy would be obtained if SAR observations were carried out more frequently in all orbit tracks. The deformation obtained in the case study indicates uplift along the west coast and subsidence with contraction around the caldera. The speed of the uplift was almost constant, but the subsidence around the caldera decelerated from 2009. A flat deformation source was estimated near sea level under the caldera, implying that deceleration of subsidence was related to interaction between volcanic thermal activity and the aquifer.

A survey of volcanic deformation on Java using ALOS PALSAR interferometric time series

Of the hundreds of volcanic centers throughout the Indonesian archipelago, few are adequately monitored for pre-eruptive activity due to socioeconomic and logistical barriers, with the result that volcanic hazards in the region are not well quantified. The advent of satellite-borne L-band synthetic aperture radar provides an opportunity for detection and measurement of volcanic deformation over broad regions in heavily vegetated tropical island arcs. We use data from the PALSAR instrument on the Japanese ALOS satellite to conduct a comprehensive survey of volcanic deformation on the Indonesian island of Java, over a time period of two years (2007–2008). To obtain the most complete, temporally continuous record of ground deformation, we use a temporally overlapping set of short-time-interval radar image pairs to produce a deformation time series. Consistent with previous results from other regions, our survey suggests that volcanoes experiencing small eruptions are typically fed by magma bodies too small and/or too shallow or deep to produce a recognizable InSAR signal. However, we identified a deformation event at Lamongan volcano which is likely linked to a magmatic intrusion at several kilometers' depth, and a second one at Slamet volcano at a shallower depth that may have been related to a subsequent eruption. This initial test of a broad application of L-band data allowed us to better define the satellite imaging criteria required for successful observation, as well as developing a useful methodology for monitoring deformation over a wide region.

Co-eruptive subsidence at Galeras identified during an InSAR survey of Colombian volcanoes (2006–2009)

Establishing a time series of deformation is one of the keys to understanding and predicting the magmatic behaviour of active volcanoes. Satellite techniques represent an increasingly useful tool for measuring volcanic deformation over timescales spanning days to decades. Colombia contains numerous young or active volcanoes, many of which are inaccessible. We use L-band (23.6 cm wavelength) radar data acquired between 2006 and 2009, to survey 15 active volcanoes along the Colombian segment of the Northern Volcanic Zone. Analysis of 100 interferograms showed that the majority of volcanoes were not deforming. However, independent interferograms display an average subsidence of 3 cm on the northeast flank of Galeras, coinciding with the January 2008 eruption. We combine InSAR, field measurements and source modelling to determine the origin, size and location of the source of subsidence at Galeras. Our results suggest that this signal was caused by deflation of the magma chamber associated with the January 2008 event. Modelling provides insight into the depth to source (~ 2 km) and a volume change (− 6.5 × 10 5 m 3) which is consistent with that derived from modelling contemporaneous tilts and the volume of material erupted. Previous studies based on various datasets support the existence of a resident/recurring chamber at this location, over a decadal timescale. Our InSAR results corroborate the hypothesis of shallow magma storage beneath Galeras and provide the first piece of evidence that can be linked to a particular eruption.

Rift zone abandonment and reconfiguration in Hawaii: Mauna Loa's Ninole rift zone

A new onshore-offshore three-dimensional seismic velocity model for the Island of Hawaii reveals a massive buried rift zone within Mauna Loa9s southeast flank, introduced here as the Ninole rift zone. This feature extends more than 60 km south of Mauna Loa9s summit, spans a depth range of ∼2–14 km below sea level, and is the probable source of the 100–200 ka Ninole volcanics in several prominent erosional hills. The ancient rift zone may stabilize Mauna Loa9s southeast flank, focusing recent volcanic activity and deformation onto the unbuttressed west flank. The upper portion of the Ninole rift zone appears to have migrated westward over time, possibly triggered by landsliding, causing its eventual abandonment in preference to Mauna Loa9s present-day southwest rift zone. Subsequently, the lower southwest rift zone broke away, tracking rift intrusions along the trace of the Kahuku detachment fault. Similar rift zone migration is thought to be under way at Kilauea volcano, and may one day lead to the abandonment of the east rift zone. Such rift zone reconfiguration is a reflection of changing stress conditions within growing volcanoes; it is probably much more common than previously assumed, and may enable the growth of large volcanic edifices such as Mauna Loa.