A volcanic structure, generally large, which is principally the result of collapse or subsidence into the top of a magma chamber during or immediately following eruptive activity (Cole et al., 2004). Collapse or subsidence is essential to form a caldera and analogue models help constrain the sub-surface features formed beneath them, caldera collapse has previously been considered as occurring on steeply inward-dipping faults (Fridrich et al., 1991).