Volcanic Ground Deformation Research Articles

An Investigation of Volcanic Ground Deformation Using InSAR Observations at Tendürek Volcano (Turkey)

Although approximately one-tenth of the world’s population lives near volcanoes, most of the 1500 active volcanoes are not monitored by ground-based instruments because of the cost and difficulty of access. Since the development of interferometric synthetic aperture radar (InSAR) in the 1990s, recent advances have allowed the near-real-time detection of surface deformations, one of the earliest markers of volcanic activity. According to the Global Volcanism Program, Turkey’s most recent eruption (involving gas and ash) occurred in the Tendürek volcano in 1885. An explosion in the Tendürek volcano, which continues to actively output gas and steam, would be a critical issue for the life and property of the people living nearby. In this context, we processed the Sentinel-1 data collected by the European Space Agency using the Stanford Method for Persistent Scatterers, and the surface deformations of the Tendürek volcano were investigated. In addition, we applied two different atmospheric correction approaches (linear phase-based tropospheric correction and the Generic Atmospheric Correction Online Service for InSAR) to reduce atmospheric effects and found that the linear phase-based tropospheric correction model produced lower standard deviation values. Subsequently, the mean deformation velocity maps, displacement time series, and deformation components in the line-of-sight direction were calculated. The results showed that the most severe subsidence was −11 mm/yr on the upper slopes of the Tendürek volcano. Although the lower slopes of the subsidence region have a lower settlement rate, the subsidence has a peak-caldera-centered location.

History‐Dependent Volcanic Ground Deformation From Broad‐Spectrum Viscoelastic Rheology Around Magma Reservoirs

AbstractGeodetic timeseries suggest that volcanoes exhibit a wide range of deformation patterns. Viscoelastic deformation around crustal magma storage zones is an expected contributor to such observations, but is challenging to characterize robustly. Here we present a novel approach to modeling crustal deformation around magma reservoirs that identifies frequency‐domain signatures of viscoelastic response for temperature‐dependent crustal rheology. We develop a transfer function that links unsteady reservoir pressure forcing to surface displacement, finding that thermomechanical properties and geometry of the magmatic system are encoded in viscoelastic response on timescales where geodetic observations are routinely made. Inhomogeneous viscoelasticity is reflected by spatially variable relaxation of host rocks that results in a viscous aureole whose size depends on the frequency spectrum of forcing. We explore viscoelastic signatures of broadband pressurization episodes, identifying a history dependence of volcano deformation in which past activity influences the stress state and surface deformation patterns of future episodes.

Routine Processing and Automatic Detection of Volcanic Ground Deformation Using Sentinel-1 InSAR Data: Insights from African Volcanoes

Since the launch of Sentinel-1 mission, automated processing systems have been developed for near real-time monitoring of ground deformation signals. Here, we perform a regional analysis of 5 years over 64 volcanic centres located along the East African Rift System (EARS). We show that the correction of atmospheric signals for the arid and low-elevation EARS volcanoes is less important than for other volcanic environments. We find that the amplitude of the cumulative displacements exceeds three times the temporal noise of the time series (3σ) for 16 of the 64 volcanoes, which includes previously reported deformation signals, and two new ones at Paka and Silali volcanoes. From a 5-year times series, uncertainties in rates of deformation are ∼0.1 cm/yr, whereas uncertainties associated with the choice of reference pixel are typically 0.3–0.6 cm/yr. We fit the time series using simple functional forms and classify seven of the volcano time series as ‘linear’, six as ‘sigmoidal’ and three as ‘hybrid’, enabling us to discriminate between steady deformation and short-term pulses of deformation. This study provides a framework for routine volcano monitoring using InSAR on a continental scale. Here, we focus on Sentinel-1 data from the EARS, but the framework could be expanded to include other satellite systems or global coverage.

Exploring the Impact of Thermally Controlled Crustal Viscosity on Volcanic Ground Deformation

AbstractVolcanoes undergoing unrest often produce displacements at the ground surface, providing an important window to interpret the dynamics of the underlying magmatic system. The thermomechanical properties of the surrounding host rock are expected to be highly heterogeneous, with key physical parameters having a strong dependence on temperature. Deformation models that incorporate nonelastic rheological behaviors are therefore heavily reliant on the assumed thermal conditions, and so it is critical to understand how the thermomechanical crustal structure affects the observed deformation field. Here, we use a series of thermo‐viscoelastic Finite Element models to explore how variations in thermal constraints (i.e., reservoir temperature and background geothermal gradient) affect surface displacement patterns when using the Maxwell and Standard Linear Solid (SLS) viscoelastic configurations. Our results demonstrate a strong variability in the viscoelastic deformation response when changing the imposed thermal constraints, caused by the partitioning of deformation and the dissipation of induced stresses. When using the SLS rheology, we identify that cumulative long‐term displacements can vary by over 20%, relative to a reference model with a reservoir temperature of 900°C and background geothermal gradient of 30 K km−1. The relative change increases to a maximum of 35% when thermal weakening of the Young's modulus is also considered. Contrastingly, the deformation patterns of the Maxwell rheology are governed by unbounded displacements and complete stress relaxation. Ultimately, we outline that uncertainties in the thermal constraints can have a significant impact on best‐fit source parameters (e.g., size and depth) and overpressure/volume‐change loading histories inferred from thermo‐viscoelastic models.

Magmatic Processes in the East African Rift System: Insights From a 2015–2020 Sentinel‐1 InSAR Survey

AbstractThe East African Rift System (EARS) is composed of around 78 Holocene volcanoes, but relatively little is known about their past and present activity. This lack of information makes it difficult to understand their eruptive cycles, their roles in continental rifting and the threat they pose to the population. Although previous InSAR surveys (1990–2010) showed sign of unrest, the information about the dynamics of the magmatic systems remained limited by low temporal resolution and gaps in the data set. The Sentinel‐1 SAR mission provides open‐access acquisitions every 12 days in Africa and has the potential to produce long‐duration time series for studying volcanic ground deformation at regional scale. Here, we use Sentinel‐1 data to provide InSAR time series along the EARS for the period 2015–2020. We detect 18 ground deformation signals on 14 volcanoes, of which six are located in Afar, six in the Main Ethiopian Rift, and two in the Kenya‐Tanzanian Rift. We detected new episodes of uplift at Tullu Moje (2016) and Suswa (mid‐2018), and enigmatic long‐lived subsidence signals at Gada Ale and Kone. Subsidence signals are related to a variety of mechanisms including the posteruptive evolution of magma reservoirs (e.g., Alu‐Dallafila), the compaction of lava flows (e.g., Nabro), and pore‐pressure changes related to geothermal or hydrothermal activity (e.g., Olkaria). Our results show that ∼20% of the Holocene volcanoes in the EARS deformed during this 5‐years snapshot and demonstrate the diversity of processes occurring.

3D multi-source model of elastic volcanic ground deformation

Developments in Interferometric Synthetic Aperture Radar (InSAR) and GNSS (Global Navigation Satellite System) during the past decades have promoted significant advances in geosciences, providing high-resolution ground deformation data with dense spatio-temporal coverage. This large dataset can be exploited to produce accurate assessments of the primary processes occurring in geologically active areas. We present a new, original methodology to carry out a multi-source inversion of ground deformation data to better understand the subsurface causative processes. A nonlinear approach permits the determination of location, size and three-dimensional configuration, without any a priori assumption as to the number, nature or shape of the potential sources. The proposed method identifies a combination of pressure bodies and different types of dislocation sources (dip-slip, strike-slip and tensile) that represent magmatic sources and other processes such as earthquakes, landslides or groundwater-induced subsidence through the aggregation of elemental cells. This approach has the following features: (1) simultaneous inversion of the deformation components and/or line-of-sight (LOS) data; (2) simultaneous determination of diverse structures such as pressure bodies or dislocation sources, representing local and regional effects; (3) a fully 3D context; and (4) no initial hypothesis about the number, geometry or types of the causative sources is necessary. This methodology is applied to Mt. Etna (Southern Italy). We analyze the ground deformation field derived from a large InSAR dataset acquired during the January 2009 – June 2013 time period. The application of the inversion approach models several interesting buried structures as well as processes related to the volcano magmatic plumbing system, local subsidence within the Valle del Bove and seaward motion of eastern flank of the volcano.

The Influence of Viscoelastic Crustal Rheologies on Volcanic Ground Deformation: Insights From Models of Pressure and Volume Change

AbstractInelastic rheological behavior, such as viscoelasticity, is increasingly utilized in the modeling of volcanic ground deformation, as elevated thermal regimes induced by magmatic systems may necessitate the use of a mechanical model containing a component of time‐dependent viscous behavior. For the modeling of a given amplitude and footprint of ground deformation, incorporating a viscoelastic regime has been shown to reduce the magma reservoir overpressure requirements suggested by elastic models. This phenomenon, however, is restricted to pressure‐based analyses and the associated creep behavior. Viscoelastic materials exhibit additional constitutive time‐dependent behaviors, determined by the stress and strain states, that are yet to be analyzed in the context of volcanic ground deformation. By utilizing a mechanically homogeneous model space and distinct reservoir evolutions, we provide a comparison of three viscoelastic rheological models, including the commonly implemented Maxwell and Standard Linear Solid configurations, and their time‐dependent behaviors from a fundamental perspective. We also investigate the differences between deformation time series resulting from a pressurization or volume change, two contrasting approaches that are assumed to be equivalent through elastic modeling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress‐based pressurization models imparting enhanced deformation relative to the elastic models, thus reducing pressure requirements. Strain‐based volumetric models, however, exhibit reduced levels of deformation and may produce episodes of apparent ground subsidence induced by source inflation or vice versa, due to the relaxation of crustal stresses, dependent on whether the reservoir is modeled to be expanding or contracting, respectively.

Assessing Eruption Forecasts Based on Volcanic Ground Deformation Events Caused by Deeper Pressure Sources

Assessing Eruption Forecasts Based on Volcanic Ground Deformation Events Caused by Deeper Pressure Sources

Multiridge Method for Studying Ground-Deformation Sources: Application to Volcanic Environments

Volcanic phenomena are currently monitored by the detection of physical and chemical observations. Generally, the ground deformation field is the most relevant shallow expression of the geometric and physical parameters variations in the magmatic reservoir. In this study, we propose a novel method for the direct estimation of the geometric parameters of sources responsible for volcanic ground deformation detected via the DInSAR technique. Starting with the biharmonic properties of the deformation field, we define an approach based on the Multiridge and ScalFun methods to achieve relevant information about both the positions and shapes of active sources, such as the Mogi source. Our methodology is definitely different from the methods currently used for modeling ground-deformation sources, mainly based on forward or inverse techniques. In fact, (i) it does not require any assumptions about the source type, and (ii) it is not influenced by the distribution of medium elastic parameters or (iii) the presence of high-frequency noise in the dataset. For synthetic cases, we accurately estimate the depth to the source within a 3% error. Finally, we study the real case of the Okmok volcano ground-deformation field and achieve results compatible with those in previous works.

Application of Machine Learning to Classification of Volcanic Deformation in Routinely Generated InSAR Data

AbstractRecent improvements in the frequency, type, and availability of satellite images mean it is now feasible to routinely study volcanoes in remote and inaccessible regions, including those with no ground‐based monitoring. In particular, Interferometric Synthetic Aperture Radar data can detect surface deformation, which has a strong statistical link to eruption. However, the data set produced by the recently launched Sentinel‐1 satellite is too large to be manually analyzed on a global basis. In this study, we systematically process >30,000 short‐term interferograms at over 900 volcanoes and apply machine learning algorithms to automatically detect volcanic ground deformation. We use a convolutional neutral network to classify interferometric fringes in wrapped interferograms with no atmospheric corrections. We employ a transfer learning strategy and test a range of pretrained networks, finding that AlexNet is best suited to this task. The positive results are checked by an expert and fed back for model updating. Following training with a combination of both positive and negative examples, this method reduced the number of interferograms to ∼100 which required further inspection, of which at least 39 are considered true positives. We demonstrate that machine learning can efficiently detect large, rapid deformation signals in wrapped interferograms, but further development is required to detect slow or small deformation patterns which do not generate multiple fringes in short duration interferograms. This study is the first to use machine learning approaches for detecting volcanic deformation in large data sets and demonstrates the potential of such techniques for developing alert systems based on satellite imagery.

A2-01 火道内マグマ後退モデルによるブルカノ式噴火に伴う山体変形(地震・地殻変動,口頭発表)

A2-01 火道内マグマ後退モデルによるブルカノ式噴火に伴う山体変形(地震・地殻変動,口頭発表)

Deposit loading and its effect on co-eruptive volcano deformation

Erupting volcanoes commonly exhibit characteristic ground deformation that is typically interpreted in terms of pressure changes of magma reservoirs within the crust. However, other processes may also be significant. Since 1995, the Soufrière Hills Volcano, Montserrat, has erupted about 1 km3 of magma over five discrete extrusive phases with clear cycles of associated ground deformation, recorded by GPS. Here we consider the contribution to deformation by loading of the ground surface with erupted deposits. We estimate topographic change and net deformation for the whole eruption to date, between November 1995 and February 2010. We derive the surface load distribution using differenced digital elevation data, which additionally enables us to constrain the budget of erupted lava. About a third of the lava erupted from Soufrière Hills since 1995 remains in subaerial, onshore deposits; more than previously thought. Another third is emplaced immediately offshore, and the remaining third has been transported further afield. We combine the deposit thickness map with representative deposit densities to calculate surface load and model the deformation response using finite elements. Our results show that net displacements accumulated over 14 years on Montserrat (tens of centimetres) could be explained by loading of erupted deposits on the flanks. The proportion of the observed deformation that can be explained by loading alone depends on crustal rheology. Using rheology structures favoured in the literature, our forward modelled displacements are remarkably similar to long-term observations, down to detail that we ascribe to localised load-topography interaction. Results suggest that the shallow crust beneath Montserrat is more compliant than usually assumed in geodetic models, with more rigid rheology at depth. Loading is largely accommodated by elastic strain in the shallow crust (top few kilometres) with negligible contribution from intra-crustal viscous flow over the time period investigated. We thus infer that the role of stress transfer from the surface load in metering magma reservoir behaviour must be negligible but may influence degassing in the shallow conduit, for example. Our findings suggest that, when volcanic ground deformation accompanies a voluminous eruption, geodetic model inversions will be misled if data are not appropriately corrected for the surface loading effect.

GPS ground deformation patterns at Mount St. Helens (Washington, USA) from 2004 to 2010

Terra Nova, 24, 148–155, 2012AbstractGPS measurements on Mount St. Helens spanning the 2004.00–2010.85 time interval, encompassing the 2004–2008 dome‐building eruption, were analysed. First, a local reference frame was derived to isolate the volcanic ground deformation from the background tectonic pattern related to the interactions between the Pacific, Juan de Fuca and North American plates. Secondly, the resulting ground deformation patterns were modelled to constrain magmatic sources. Results suggest a vertically elongated magma chamber centred at 8–9 km depth beneath the summit area that deflated during the beginning of the dome growth and inflated since January 2008, indicating that the same primary magma reservoir was active both during and after the eruption in a magmatic system that is persistent over the time.

Seasonal tropospheric influence on SAR interferograms near the ITCZ – The case of Fogo Volcano and Mount Cameroon

The potential of differential SAR interferometry (DInSAR) to measure volcanic ground deformation is widely recognized, despite several limitations still hindering its use in operational volcano monitoring, one of the most critical being water vapor change in the troposphere. In this paper we investigate tropospheric influence on SAR interferograms for two African active volcanoes strongly affected by the oscillation of the Inter-tropical convergence zone (ITCZ). Fogo Island (∼40,000 inhabitants), located in the southwestern part of the Cape Verde archipelago, is a 30-km-wide active volcano that last erupted in 1995. Mount Cameroon, with approximately 300,000 people living in its immediate surroundings, is the most active volcanic center of the 1600 km-long Cameroon volcanic line, counting seven eruptions over the last century. We analyze 72 SLC ASAR images of Fogo, acquired by ENVISAT from June 2005 to December 2007, and 14 SLC ASAR images of Mount Cameroon, acquired from July 2004 to January 2008. A total of 274 two-pass interferograms, computed from the SLC images, were used for fringe counting and least-squares data adjustment, allowing the estimation of a relative phase delay for each image. We then compare the InSAR-retrieved phase delays with two independent calculations of precipitable water vapor (PWV) in the troposphere, using MODIS and GPS, and observe that all time-series, for both regions under study, match up the ITCZ seasonal oscillation. We conclude that most (if not all) of the phase delays observed are due to water vapor change in the troposphere.

On the relative importance of self‐gravitation and elasticity in modeling volcanic ground deformation and gravity changes

Elastic half‐space models, widely used to interpret displacements and gravity data in active volcanic areas, usually compute the displacement response to dilatational sources that simulate a change in pressure of the magma chamber. Elastic‐gravitational models allow the computation of gravity, deformation, and gravitational potential changes due to pressurized magma cavities and intruding masses together. This type of model takes into account the mass interaction with the self‐gravitation of the Earth through coupling between model equations. We perform a dimensional analysis of the elastic‐gravitational model estimating the magnitude of intrusion mass and coupling effects at the space scale associated with volcano monitoring. We show that the intrusion mass cannot be neglected in the interpretation of gravity changes while displacements are primarily caused by pressurization. Therefore the intrusion of mass, together with the associated pressurization of the magma chamber, produces distinctive changes in gravity that could be used to interpret gravity changes without ground deformation and vice versa, depending on what type of source plays the main role in the intrusion process. Theoretical experiments indicate that mass and self‐gravitation could produce changes in the magnitude and pattern of predicted gravity that may be above microgravity accuracy. Application of the elastic‐gravitational model to interpret geodetic precursors observed at Mayon volcano (Philippines) prior to the eruption of 2001 shows that inversions increase in precision by using this model. Therefore our elastic‐gravitational model is a refinement of purely elastic models and can better interpret gravity and deformation changes in active volcanic zones.