Quantifying salt extrusion versus surface salt flow rates at Mt. Sedom to gain insights on its mechanics and potential external atmospheric forcing

Abstract

The study of salt tectonics is essential due to its relevance in locating hydrocarbon reserves, providing storage for fuels and waste, and offering insights into extraterrestrial geology. Despite decades of research, salt extrusion and flow rates at the surface remain poorly characterized, even with frequent confusing terminology. In our study, we aim to separate both phenomena at one of the best test sites on Earth, Mt. Sedom, a prominent salt extrusion site in a tectonically active basin. We utilized InSAR (Interferometric Synthetic Aperture Radar) techniques to measure surface salt motion with high temporal resolution, analyzing 9.5 years of Sentinel-1 data to derive both vertical and horizontal displacement components. Our approach improves previous estimates that used only line-of-sight (LOS) measurements. We are able to estimate vertical uplift rates directly above the salt extrusion channel location inferred using mechanical modeling. We propose that these estimates are a much closer representation of the actual salt extrusion rates, and largely independent of the typically overlapping surface gravity-driven flow dynamics. The InSAR time-series suggests that thermal expansion is a first-order driver of the observed seasonal uplift and subsidence patterns. Moreover, for the first time in Mt. Sedom, displacement changes in response to weather (rainfall) were inferred to be statistically significant. We conclude that any rainfall event, regardless of its magnitude, might be sufficient to enhance salt flow rate. This can be explained as a result of salt dissolution and increased gravity-driven downslope movement in the salt glacier as the salt becomes wet, due to increased surface load or reduced viscous/frictional forces. By integrating InSAR measurements, mechanical modeling, and meteorological data, this study provides new constraints on surface salt motion at Mt. Sedom, improving our understanding of its driving mechanisms. Most importantly, our results reveal an immediate response of salt motion to rainfall, providing new insights into interactions between atmospheric and crustal processes.