Surface Deformation and Salt Budget of an Active Salt Fountain, Finu in the Zagros Mountains, Iran, Using Persistent Scatterer Interferometry

Abstract In subaerial salt diapirs, salt buoyancy drives the vertical flow of salt in the feeder, salt extrusion, and gravity spreading on the surface. The shape of these diapirs is controlled by the balance between buoyancy forces, gravity spreading on the surface, and surface dissolution of the salt. While salt dissolution is a surface process that can be directly observed, the rate of salt supply from depth is more difficult to constrain. In this study, we mapped the surface deformation of the Finu salt fountain in the Zagros Mountains of Iran using Persistent Scatterer Interferometry (PSI) of Sentinel-1 SAR data from 2014 to 2018 and calculated the volume change over this period. The observed deformation signal indicates uplift at the central dome and outward spreading at the flanks. Our PSI time series shows no correlation between these surface motions and variations in temperature and precipitation, indicating that the deformation is primarily driven by internal salt dynamics. The extracted 2D velocity vectors along an east–west (E–W) trending swath profile across the diapir vary in magnitude with distance from the diapir center and with local slope, reflecting both salt supply from the subsurface and its gravity spreading. The 2D displacements reveal a change in cross-sectional area along this profile of +9.80 ± 0.97 m²/y. Integrating this value over the diapir’s extent yields a total volume change of +38.3 ± 3.8 × 10³ m³/y. Using plausible estimates for salt dissolution rates, we estimated a total salt flux of 146.2 ± 3.8 × 10³ m³/y, corresponding to extrusion from a 1.7 km diameter feeder at an average rate of 64 ± 2 mm/y. This study quantifies the salt supply in an axisymmetric salt fountain based on surface deformation data. Our findings improve the understanding of salt-spreading mechanisms and contribute to more accurate assessments of salt budgets in diapiric systems.