An outcrop and microtextural study of sand volcanoes from the Namurian of County Clare is presented. Sand volcanoes occur on top of mud-rich slumps that are interpreted to have loaded the sediment pile and caused rapid compaction and fluid expulsion from the underlying units. Fluids migrated into the most permeable sand-rich bodies in the slump, and fluidized grains were then extruded at the sediment-water interface. In some cases, a laterally extensive extrusive sheet of silt and sand developed, with volcanoes located at focused sites of sediment expulsion. From microtextural studies, several (geologically short-lived) episodes of sediment and fluid expulsion are recognized as distinct, normally graded silt to sand-size beds separated by clay-rich beds. The clay-rich beds may either represent background sedimentation between expulsion events or may have been part of the extruding fluidized sediment itself.