Cyclic caldera collapse: Piston or piecemeal subsidence? Field and experimental evidence

Many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution. On Gran Canaria (Canary Islands), the Miocene Tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone-sheet swarm, obscuring intracaldera structural relations. Extracaldera radial and circumferential faults and dikes are well exposed. We used field data and experiments scaled to the island of Gran Canaria to clarify the poorly understood structural, temporal, and genetic relationship of peripheral faults to the central caldera. The experimental setup comprises a cone of medium-grained sand in which a rubber balloon was repeatedly inflated and deflated. Balloon inflation resulted in updoming and a dominantly radial fault pattern, whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks. A complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the Tejeda caldera on Gran Canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes.