Inflation Dynamics and Magma Recharge within the Svartsengi Volcanic System (SW Iceland) Inferred from GNSS and InSAR Data

GNSS and InSAR observations have detected almost continuous inflation since October 2023 within the Svartsengi Volcanic System (SW Iceland). Inflation was interrupted by rapid deflation and concurrent dike intrusions, resulting in a total of nine eruptions (as of January 2026, the time of writing) within the Sundhnúkur crater row and its extension.

Here, we focus particularly on inflation events to improve our understanding of magma supply and the evolution of the magmatic system following each diking event/eruption. The InSAR observations were acquired from multiple spaceborne SAR satellite missions (e.g., Sentinel-1, TerraSAR-X, and COSMO-SkyMed) while the GNSS observations were obtained from the well-established geodetic network operating at and surrounding the Svartsengi volcanic system.  These dataset were jointly modeled using a variety of source geometries (e.g., spherical, sill-type, and ellipsoidal) embedded in a homogeneous, elastic half-space, allowing us to assess how source shape affects the inferred depth and volume of inflation.

Analysis of the modeling results reveals a clear pattern. The earliest inflation episodes (up to February–March 2024) were relatively short, lasting several weeks, and exhibited strong variability in both inferred source depth and recharge volume from one inflation episode to another across all tested source geometries, before triggering a new dike intrusion or eruption. Across the three tested source geometries, inferred source depths ranged as follows: 3.5–4.5 km for spherical sources, 3–3.5 km for ellipsoidal sources, and 4–5.5 km for sill-type sources. Corresponding volumes are approximately ranging from 4 to 21 × 10⁶ m³, 3 to 19 × 10⁶ m³, and 5 to 24 × 10⁶ m³ for spherical, ellipsoidal, and sill-type sources, respectively.

Since March 2024, the system appears to have become more stable: although absolute depth and volume estimates still depend on the assumed source geometry, the inferred depth and volume for each individual geometry have remained fairly consistent across successive events. Specifically, depths have stabilized around 3.9 ± 0.2 km for spherical sources, ~3 ± 0.2 km for ellipsoidal sources, and 4.7 ± 0.1 km for sill-type sources, with corresponding volumes approximately ranging from 18 to 21× 10⁶ m³, 15 to 18 × 10⁶ m³, and 22 to 25 × 10⁶ m³, respectively.

A detailed study of the volcanic system and its temporal evolution can provide critical insights into the processes governing magma accumulation. Geodetic data form the cornerstone of this analysis, and when combined with seismic, petrological, and other multidisciplinary observations, they allow a more accurate interpretation of the system’s pre-eruptive behaviour. Linking system evolution with these multi-parameter observations enables better characterization of inflation episodes, supporting improved forecasting and more reliable assessment and mitigation of associated volcanic hazards.