The 1999 eruption of Cameroon Mountain was restricted to two sites and controlled by fissures subparallel to one another. Brittle failure, vertical displacement, horizontal displacement and ground deflation are the main types of ground deformation around these sites. The eruptive vents at both sites have a NE-SW trend parallel to the principal eruptive fissures and brittle discontinuities in rock bodies in this vicinity. SH (greatest horizontal stress) is inferred to have a SW-NE trend parallel to the direction of vent migration and fracture propagation.