Geology topics
Tara Shreve
Publications and source records attributed to Tara Shreve.
Vent-specific unrest at Pavlof Volcano, Alaska: Insights from multidisciplinary data
Pavlof Volcano, a frequently active volcano in the Aleutian arc, has erupted six times between 2007 and 2022. Many Pavlof Volcano eruptions lack detectable precursory seismicity or ground deformation, making them challenging to forecast. Since 2007, these eruptions have ranged from Strombolian to Subplinian (VEI 2–3), with their characteristics seemingly related to their active vent location. Summit vent eruptions tend to be abrupt and explosive, while southeast flank vent eruptions tend to be more effusive and longer-lived. To better understand Pavlof Volcano’s plumbing system and improve eruption forecasts, we integrate geophysical, petrologic, and satellite-based thermal infrared and gas data to conduct a multidisciplinary data synthesis for eruptions between 2007 and 2022. Notably, a recently developed volcano seismicity detection model reveals unique pre- and syn-eruptive seismic tremor regimes associated with each vent system. The summit vent eruptions show greater tremor diversity and resurgent eruptive behavior, whereas the southeast flank vent eruptions show a steady tremor transition over a single eruptive phase. We use local infrasound data and air-to-ground coupled waves to build explosion catalogs, revealing gas-rich explosions during the 2021–2022 eruption from the summit vent, which was previously thought to be inactive during that eruption. Whole-rock composition and ash analyses indicate a near-uniform basaltic andesite composition spanning multiple eruptions, and a consistent anomalous presence of altered olivines in erupted material. We use these findings to propose a new conceptual model for Pavlof Volcano’s plumbing system: a shallow T-junction outlet controlling seismic tremor diversity and the partitioning of gas-charged magma; and an elongated, heated conduit transporting magma from depth and storing partly molten, residual magma between eruptions. We suggest that magma ascent rate and vent sealing modulate eruption style at Pavlof Volcano, where the T-junction directs rapidly ascending, gas-rich magma to the summit vent, and diverts slower rising, gas-poor magma towards the southeast flank vent.
The utility of TerraSAR-X, TanDEM-X, and PAZ for studying global volcanic activity: Successes, challenges, and future prospects
TerraSAR-X (TSX), TanDEM-X (TDX), and PAZ Synthetic Aperture Radar data have been used at over 120 volcanoes to assess surface characteristics and change over time. We examine previous work, adding additional examples to understand where and when these data are most useful for volcanology. We focus on volcanoes as part of the Committee on Earth Observation Satellites (CEOS) Volcano Demonstrator Project. TSX/TDX/PAZ data provide a valuable means of detecting small surface changes from amplitude images and topographic changes from bistatic TSX/TDX data. For short temporal and perpendicular baselines, TDX/TSX/PAZ can also provide useful deformation data, even in presence of vegetation. No global background mission currently acquires TSX/TDX/PAZ data at volcanoes: 70 % high spatial resolution data, limiting their suitability for studying pre-eruptive unrest. Coordinated targeting by SAR constellations of priority volcanoes would provide data and insights valuable for forecasting eruptions and associated hazards.
A global assessment of SAOCOM-1 L-band stripmap data for InSAR characterization of volcanic, tectonic, cryospheric, and anthropogenic deformation
SAOCOM-1 is an L-band (23.5 cm) synthetic aperture radar (SAR) constellation made up of two satellites launched in 2018 and 2020 by Comisión Nacional de Actividades Espaciales (CONAE, Argentina). In this contribution, we present a global summary of interferometric SAR (InSAR) observations of ground deformation with SAOCOM-1 stripmap data for tracking volcanic, tectonic, glacier, and anthropogenic deformation. These examples include: 1) episodes of unrest at volcanoes in the Aleutian Islands, Southern Andes, and Italy, with line-of-sight (LOS) deformation from 4 cm/yr in InSAR time series to ~70 cm in interferograms; 2) dike intrusions in Hawai’i; 3) earthquakes in the Andean fold and thrust belt and the East Anatolian fault; 4) ice flow of the Southern Patagonia icefield; and 5) subsidence due to lithium brine extraction in the Salar de Atacama basin (northern Chile). Comparisons between SAOCOM-1, ALOS-2 SM3, Sentinel-1, and TerraSAR-X/ TanDEM-X/PAZ (TSX/TDX/PAZ) mean velocities from InSAR time series show a 1:1 ± 3% correlation in the LOS velocity, which highlights the high accuracy of SAOCOM-1 data. The minimum deformation that we measured in individual interferograms is 4 ± 0.6 cm. One limitation of SAOCOM-1 is the lack of a global acquisition program, which reduces its global and broader applications. Considering the repeat periods, background observation program, and lack of a controlled orbital tube, the best suited targets for SAOCOM-1 InSAR are two. First, volcanoes that deform with secular rates located in vegetated regions in mid- and high-latitudes, and/or that undergo transient episodes of fast deformation in which C-band coherence is lost quickly. Second, glaciers where coherence can be sustained during the repeat period of eight days.
Understanding the drivers of volcano deformation through geodetic model verification and validation
Volcano geodesy often involves the use of models to explain observed surface deformation. A variety of forward models are used, from analytical point sources to numerical simulations that consider complex magma system geometries, topography, and material properties. Various inversion methods can then be used to relate observed volcano data to models. Ideally, forward models should be verified through intercomparison, to check for implementation errors and quantify the error induced by any approximations used. Additionally, forward models and inversion methods should be validated through tests with synthetic and/or real data, to determine their ability to match data and estimate parameter values within uncertainty. However, to date, there have not been comprehensive verification and validation efforts in volcano geodesy. Here, we report on the first phase of the Drivers of Volcano Deformation (DVD) exercises, which were designed to build community involvement through web-based exercises involving calculations of static elastic displacement around pressurized magma reservoirs. The forward model exercises begin with a spherical reservoir in a homogeneous half space, then introduce topography, heterogeneous elastic properties, and spheroidal geometries. The inversion exercises provide synthetic noisy surface displacement data for a spherical reservoir in a homogeneous half space and assess consistency in estimates of reservoir location and volume/pressure change. There is variability in the results from both forward modeling and inversions, which highlights the strengths and limitations of different forward models, as well as the importance of inversion method choice and uncertainty quantification. This first phase of the DVD exercises serves as a community resource and will facilitate further efforts to develop standards of reproducibility.