Continuous subsidence of Dallol volcano caused by magmatic, hydrothermal, and salt dissolution processes: insights from InSAR observations

Abstract

The Dallol volcano on the axis of the Erta Ale ridge (Afar rift) offers an ideal opportunity to study the interaction between magmatic and hydrothermal processes. Volcanic activity in Dallol has developed in an area below sea level with a salt plain. Dallol has been actively deforming since InSAR measurements started in the area in 2004. However, the source of deformation under Dallol remains unclear. We present a new InSAR study of Dallol from 2014 to 2023 showing at least three concentric deformation signals of range increase consistent with subsidence with rates ranging 23–43 mm/yr in the satellite Line-of-Sight. The main subsidence occurs at Dallol volcano, and two smaller maxima occur at the Black Mountain and the Bubbling Pool areas to the south and southwest of Dallol, respectively. Our modeling indicates that the deformation is caused by contraction of three sill-shaped sources (Okada tensile dislocations) at depths ranging 0.6–1.5 km, each with a volume contraction in the range 1.8–5.5 × 10 ⁴ m ³/yr. Time series analysis shows that the subsidence at Dallol volcano and Black Mountain was continuous and linear in time. Furthermore, an integrated observation of InSAR with the geology, resistivity image and seismic reflection of the area suggest that the 1.5 km deep source under Dallol is the cooling and contraction of a magma reservoir. At Black Mountain (1 km deep) and Bubbling Pool (0.6 km deep), the data suggest that subsidence is due to either a pressure decreases in the shallow hydrothermal system and/or salt dissolution.

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