Continuous Subsidence of Dallol Volcano (Danakil Depression) as a result of magmatic and hydrothermal interaction: Insights from InSAR Observation

Axial rift volcanoes characterised by an active magmatic and hydrothermal system offer a unique opportunity to study the interaction between these processes. The Dallol volcanic and hydrothermal area is situated in the Afar rift, on the axis of Erta Ale ridge, in a depressed salt plain. Dallol has been experiencing deformation at least since the first dike intrusion observed by InSAR in 2004. Here, we present the results of a new InSAR analysis of Dallol between 2014 and 2023, and inverse modelling of the observed deformation. We used SAR data from the ESA´s Sentinel 1A/B ascending (014) and descending (079) orbits to produce over 651 interferograms. Then we obtained InSAR average velocity maps revealing the presence of three closely spaced and concentric deformation signals of a range increase, consistent with subsidence, of up to 40 mm/yr in the satellite Line-of-Sight (LOS). The main deformation signal corresponds to the Dallol crater, while the two smaller maxima occur on the bishophite precipitating Black Mountain area south of Dallol and at the location of a circular pool at the edge of the salt plain, west of the crater. Our modelling results indicate that the deformation sources can be explained by contractions of three Okada tensile dislocation sources situated at different shallow depths, ranging between 0.7-1.7 km, with a length of 1-3 km and volume decrease of 1-3x10^-4 km³/yr. Time series analysis also shows that the subsidence pattern was about linear while small seasonal fluctuation patterns are identified at the two smaller maximas. We interpret that the main subsidance at the Dallol crater is likely caused by the depressurisation of shallow sills, while a possible contribution to the defomration from the hydrothermal system due to seasonal flooding is envisaged for the other two maximas.