Geothermal Geology of Silali Volcano in Kenya

Abstract

Silali is the largest and trachytic caldera volcano in the axis of the northern Kenya Rift Valley. This paper describes the results from examination of existing data and detailed geological exploration by the geology team of GDC. The study involved geological mapping of the rock formations, structural mapping and geothermal manifestations well as hydrogeological and volcanological studies of the volcano and sampling of rocks for thin section cutting and petrographic analysis. Fieldwork was carried out in the month of May and July 2010. Basalt is one of the most common types of lava in Silali, manifested mainly as flank fissure basalts and flood basalts. Basalts are aphiric or porphritic and vesicular. The Silali Trachytes are both silica-oversaturated and silica under saturated. In the post caldera group increasing differentiation is thought to have resulted in progressive silica under-saturation. The Blackhill Trachytes are among the youngest lavas are critically under-saturated with respect to silica. The latest activity from a satellite vent on the northern slopes of Silali is basaltic in composition and was erupted about 200-300 years BP. The presence of a still active heat source to sustain a geothermal system(s) indicates that there is a geothermal resource in the area that can be commercially exploited.