Fig. 4: Conceptual model illustrating phreatomagmatic eruptions in Tharsis, resulting in hydrothermal circulation.

a 3D view of a lava flow advancing over an ice-rich layer, with flow direction indicated by white dashed arrows. Cross-sections of the model depict a partially solidified lava flow, showing a solid crust both on the surface and at the base, enclosing a molten lava core. The surface terrain is derived from HiRISE DEM data (stereo pair: HI_034172_1880 and HI_035596_1880) and vertically exaggerated 30 times. b Schematic representation of the inferred process leading to rootless eruptions. The molten core of the lava flow concentrates in local topographic depression, heats the underlying ice-rich layer, causing steam generation, and consequently, triggers explosive phreatomagmatic eruptions. c Close-up view of the associated hydrothermal system powered by the lava-water ice interactions, leading to the formation of hydrated minerals.