We investigate the spatial relationship between self-potential (SP), soil CO2 flux, and temperature and the mechanisms that produce SP anomalies on the flanks of Masaya volcano, Nicaragua. We measured SP, soil CO2 fluxes (<1 to 5.0 x 104 g m-2 d-1), and temperatures (26 to 80oC) within an area surrounding a normal fault, adjacent to Comalito cinder cone (2002-2003). These variables are well spatially correlated. Wavelengths of SP anomalies are =100 m, and high horizontal SP gradients flank the region of elevated flux and temperature. Carbon isotopic compositions of soil CO2 (d13C = -3.3 to -1.1 ?) indicate a deep gas origin. Given the presence of a deep water table (100 to 150 m), high gas flow rates, and subsurface temperatures above liquid boiling points, we suggest that rapid fluid disruption is primarily responsible for positive SP anomalies here. Concurrent measurement of SP, soil CO2 flux, and temperature may be a useful tool to monitor intrusive activity.