A collapse is triggered by the emptying of the magma chamber beneath the volcano , sometimes as the result of a large explosive volcanic eruption ( see Tambora in 1815 ) , but also during effusive eruptions on the flanks of a volcano ( see Piton de la Fournaise in 2007 ) or in a connected fissure system ( see Bárðarbunga in 2014 – 2015 ) . If enough magma is ejected , the emptied chamber is unable to support the weight of the volcanic edifice above it . A roughly circular fracture , the " ring fault " , develops around the edge of the chamber . Ring fractures serve as feeders for fault intrusions which are also known as ring dikes . Secondary volcanic vents may form above the ring fracture . As the magma chamber empties , the center of the volcano within the ring fracture begins to collapse . The collapse may occur as the result of a single cataclysmic eruption , or it may occur in stages as the result of a series of eruptions . The total area that collapses may be hundreds or thousands of square kilometers
Tambora
1815 eruption of Mount Tambora
Caldera