This uplift created a structural dome with dips that radiate away from the geographic center of the structure. Uplift caused deformation, landsliding and consequent collapse of the top of the edifice. Subsequently, the summit basin was further excavated when pyroxene rhyolite was erupted 23.5 ka as pumice fallout and pyroclastic flows that originally covered much of the mountain. The thermal areas vent through a variety of lithologies, including rhyolites, siltstones and a small block of Precambrian mica schist that crops out in a deep canyon cut into the central part of the uplift. There are no obvious structural controls on the distribution of fumaroles.
Thermal pools contain mixtures of shallow groundwater and fumarolic condensate.
Hot or cold springs unrelated to fumaroles were not found. Isotopic and ncg ratios suggest that the steam is derived from a reservoir of air-saturated groundwater derived from winter rains in the lowland, possibly mixed with some fossil Red Sea water left over from earlier periods of marine incursions. Shallow wells in the alluvial fans to the immediate west of Alid yield waters with isotopic compositions consistent with some recharge from the Eritrean Plateau.