The Investigation of the Geothermal Potential at the Silali Volcao, Northern Kenya Rift, Using Electromagnetic Data
The Silali volcano is one among a number of volcanoes found along the axis of the Kenya rift system that has experienced immense volcanism and faulting that formed a huge caldera at its summit. In this study, we investigate the resistivity distribution within the Silali volcano region in order to define a magma chamber that was the source of young lava flows covering the region and to better describe the geologic and structural features or faults around this region that may allow fluid movement. The data reveal a magma chamber beneath the caldera and a northeast trending fault west of the volcano in the Kapedo region. Potential fluid circulation zone within the caldera region are also evident. The depth to the magma chamber is estimated from the deeper low resistivity zone to be about 6 km from the surface. A low resistivity zone less than 20 ohm-m, at 1–2 km depth is interpreted to be a low temperature clay (smectite) alteration zone resulting from fluid circulation as heat is transferred to shallower depth. The resistivity then increases abruptly beneath the inferred low temperature alteration zone and this increase in resistivity is interpreted as a change from clay mineralization to a chlorite-dominated system producing the observed decrease in resistivity. The decrease in conductivity may also imply a decrease in permeability due to decreasing connectivity of conductive fluids. The resistivity changes with depth could be temperature dependent and the inferred chlorite zone may suggest a temperature above approximately 240 °C. The deeper low resistivity zone is interpreted as molten rocks and can be interpreted to indicate temperatures above 700 °C of the magma body at a depth of 6 km.