Baseline monitoring of volcanic regions with little recent activity: application of Sentinel-1 InSAR to Turkish volcanoes

Abstract

Volcanoes have dormancy periods that may last decades to centuries meaning that eruptions at volcanoes with no historical records of eruptions are common. Baseline monitoring to detect the early stages of reawakening is therefore important even in regions with little recent volcanic activity. Satellite techniques, such as InSAR, are ideally suited for routinely surveying large and inaccessible regions, but the large datasets typically require expert interpretation. Here we focus on Turkey where there are 10 Holocene volcanic systems, but no eruptions since 1855 and consequently little ground-based monitoring. We analyse data from the first five years of the European Space Agency Sentinel-1 mission which collects data over Turkey every 6 days on both ascending and descending passes. The high relief edifices of Turkey’s volcanoes cause two challenges: 1) snow cover during the winter months causes a loss of coherence and 2) topographically-correlated atmospheric artefacts could be misinterpreted as deformation. We propose mitigation strategies for both. The raw time series at Hasan Dag volcano shows uplift of ~ 10 cm between September 2017 and July 2018, but atmospheric corrections based on global weather models demonstrate that this is an artefact and reduce the scatter in the data to < 1 cm. We develop two image classification schemes for dealing with the large datasets: one is an easy to follow flowchart designed for non-specialist monitoring staff, and the other is an automated flagging system using a deep learning approach. We apply the deep learning scheme to a dataset of ~ 5000 images over the 10 Turkish volcanoes and find 4 possible signals, all of which are false positives. We conclude that there has been no cm-scale volcano deformation in Turkey in 2015–2020, but further analysis would be required to rule out slower rates of deformation (< 1 cm/yr). This study has demonstrated that InSAR techniques can be used for baseline monitoring in regions with few historical eruptions or little reported deformation.

Minimum Detectable Mass and Volume Fluxes During Magmatic Recharge at High Prominence Volcanoes: An Application to Erciyes Dağ Volcano (Turkey)

“…We determine mass and volume changes upon reservoir recharge for given source pressurisation (ΔP) and source density change (Δρ) at the detectability limits of joint gravimetric and geodetic field surveys. We set the limits to 0.01 m for vertical surface displacements and 0 ± 5 μGal (1μ 10 -8 m s −2 ) for residual gravity changes based on the typical sensitivity of field instrumentation and survey protocols as well as constraints from remote sensing of volcanoes in the CAVP (Biggs et al, 2021). The minimum detectable volume flux into the reservoir is given by McTigue (1987):…”

“…These findings relate to the significant source volume increase of 2-5 × 10 -3 km 3 upon magma recharge at Erciyes Dağ without observable surface displacement or residual gravity variations. Under the reasonable assumption that magma reservoir replenishment at Erciyes Dağ occurs below the detection limit of surface uplift velocities of 0.01 m yr −1 (Biggs et al, 2021), the reservoir may currently sustain eruptable magma if deduced mass changes are taken as annual fluxes. This "stealth" magma flow into the reservoir matches and exceeds reported magma fluxes at several intermediate and silicic stratovolcanoes with repose times of 100-1000s of years (e.g., Parinacota, Soufrière Hills volcano and Mt.…”

Investigating Stress Transfer Between the Tuz Gölü Fault Zone and Hasan Dağ Volcano (Turkey)

“…Exact quantification of the current state of pressurisation of Hasan Dağ's magma reservoir is beyond the scope of this study and possible variations in reservoir pressure due to magma influx and rejuvenation or volatile loss are hence neglected. Although InSAR data from the European Space Agency Sentinel-1 mission between 2014 and 2020 show annual ground displacement velocities at Hasan Dağ below the detectabilty limit of 1 cm yr −1 (Biggs et al, 2021), the volcano's high prominence and crustal mechanics of the CAVP could contribute to significant volumes of stealth magma accumulation at depth (Males and Gottsmann, 2021) at the geodetic detectability limit.…”

Strategies for improving the communication of satellite-derived InSAR ground displacements

“…The aim is to provide users with tools that support interrogation of the data, with a particular focus on distinguishing between atmospheric features and volcanic deformation (e.g. Pinel et al, 2011;Ebmeier et al, 2018;Biggs et al, 2021). We present new Sentinel-1 InSAR results in the context of historical observations of volcano deformation (as described in Ebmeier et al, (2018)) organised according to volcano numbers from the Smithsonian list of Holocene volcanoes 240 (Global Volcanism Program., 2022).…”