Inflation of Okmok Volcano During 2008–2020 From PS Analyses and Source Inversion With Finite Element Models

Okmok volcano, located on northeastern Umnak Island along the eastern end of the Aleutian island arc, is one of the most active volcanoes in Alaska, producing multiple eruptions in the past century. The most recent eruption, which occurred during July–August of 2008, was the most explosive since the early nineteenth century. In the years following the 2008 eruption, Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations indicate that Okmok has inflated at a variable rate of 40–195 mm/yr. In this study, we investigate the post-eruptive deformation of Okmok (2008–2020) using InSAR and GNSS. L-band ALOS-2, C-band Sentinel-1/Envisat and X-band TerraSAR-X data are analyzed with Persistent Scatterer (PS) InSAR method. The deformation time series calculated from InSAR and GNSS are assimilated into finite element models using the Ensemble Kalman Filter to track the evolution of the magma system through time. The results indicate that the InSARderived deformation history can be well explained by a spatially stable magmatic source located in the central caldera, at about 3 km beneath the sea level, which is also believed to be the same source that produced the 1997 and 2008 eruptions. Magma accumulation in the reservoir is about E 0.08 km 3 from 2008 to 2020, which is about 160% and about 60% of the total reservoir volume changes during the 1997 and the 2008 eruptions, respectively. Plain Language Summary Precise mapping of volcano deformation allows for identification and modeling of the source location, shape, and pressure change within a magma reservoir of the volcanic system. Hence, monitoring ground surface deformation is a critical part in volcano study and eruption forecasting. In this study, we map the deformation history of Okmok volcano since its 2008 eruption using InSAR. The produced displacement time series are then used to track the magmatic pressure accumulation in the magmatic reservoir with numerical models. Our InSAR measurements show that Okmok has been undergoing persistent inflation with time-varying rates since the last eruption in 2008. The cumulative volume change during 2008–2020 is ∼160% and ∼60% of the total volumes of the 1997 The measured deformation suggests the magmatic source as that accounting for the pre-2008 eruptions. and the 2008 eruptions, respectively.