Return From Dormancy: Rapid Inflation and Seismic Unrest Driven by Transcrustal Magma Transfer at Mt. Edgecumbe (L’úx Shaa) Volcano, Alaska

Abstract

Located in Southeast Alaska, the home to about 73,000 people, or 10% of the state's population, Mt. Edgecumbe (976 m, L'úx Shaa in Lingít) is part of the Mt. Edgecumbe Volcanic Field on Kruzof Island on the west side of Sitka Sound (Figure 1). The eastern shore of Sitka Sound, about 25 km away from Mt. Edgecumbe, is home to the almost 8,500 residents of Sitka.On 11 April 2022, a Sitka resident noted that the openly available Alaska Earthquake Center (AEC) location for an M2.1 earthquake was under Mt. Edgecumbe and inquired with Alaska Volcano Observatory (AVO) contacts whether this earthquake is related to the volcano or, as previously suggested for seismicity in the region, purely tectonic. As this dormant volcano is not monitored with a dedicated geophysical instrument network, the review of seismicity relies on the broadly distributed regional seismic network, and the related location uncertainties. Activity recorded by the closest seismograph SIT, 25 km away in Sitka, indicated that a seismic swarm started about 02:00 a.m. AKDT on 11 April 2022. Earthquakes located by the AEC range in magnitude from 1.0 to 2.7 and appear broadly distributed to the northeast of Mt. Edgecumbe near the eastern rim of Crater Ridge (Figure 1, red circles in inset). This swarm, with estimated depths ranging from about 1 to 12 km, was preceded by a burst of located seismic activity in 2020 that began with an M3.0 earthquake on 2020-01-02 and lasted until about

Versatile Modeling Of Deformation (VMOD) Inversion Framework: Application to 20 Years of Observations at Westdahl Volcano and Fisher Caldera, Alaska, US

“…Similar biases have been observed by Grapenthin, Cheng, et al. (2022) at Mount Edgecumbe where a dipping sill could explain the deformation pattern observed in the descending geometry for a preliminary analysis but it was not able to explain the deformation patterns observed in two ascending images. In their final analysis, the most probable model indicates a transcrustal migration of magma between a contracting dipping sill at 20 km and a inflating point source at 10 km.…”

“…Our results suggest a depressurizing spheroid for Fisher Caldera ∼4–6 km deep, contracting at a rate of ∼2–3 Mm 3 /yr, and a pressurized spherical source for Westdahl volcano ∼7–8 km deep, inflating at a rate of ∼5 Mm 3 /yr. The VMOD framework has been used for other volcanic unrest (Grapenthin, Cheng, et al., 2022) demonstrating the advantages of jointly inverting multiple data sets using multiple source models. In the future, we envision VMOD expansions with more geodetic models and new inversion algorithms that can capture the physics of subsurface processes.…”

“…However, especially with the proliferation of InSAR through open data, surface deformation is now often detected by more than one geodetic technique (for instrumented volcanoes), or in both ascending and descending directions of SAR satellites. This can reveal otherwise unrecognized complexity of the deformation field (Grapenthin, Cheng, et al., 2022), requiring straightforward modeling of multiple deformation sources that might act at the same time.…”

“…We complemented these observations with summer to summer interferometric pairs from the Sentinel 1 A/B mission spanning 2016 to 2021 (Figure 5). We obtain the interferometric pairs (Figure S18 in Supporting Information S1) from the Alaska Satellite Facility's vertex portal (Kennedy et al, 2021) and use interferograms with high coherence values (>0.7) to generate InSAR time series with MintPy (Yunjun et al, 2019) as detailed in Grapenthin, Cheng, et al (2022). We downsample the resulting cumulative displacements using the quadtree method described above to reduce the computational cost.…”

“…VMOD has been successfully applied to analyze deformation at several volcanoes (e.g., Cheng & Grapenthin, 2024;Grapenthin, Cheng, et al, 2022;Grapenthin, Kyle, et al, 2022) and to analyze deformation around a reinjection well (Graves et al, 2023). In this paper, we introduce its architecture and use, demonstrate its abilities in a series of verification and validation exercises, and use VMOD to infer a new magmatic source model for Westdahl volcano (an informal name for the volcano under Westdahl and Faris Peaks, Alaska) and Fisher Caldera on Unimak Island, Alaska, by jointly inverting continuous and campaign GNSS and InSAR data to constrain a multi-source model.…”