The location of vents and fissures primarily reflects the stresses within the volcano. Why stresses in Galapagos volcanoes should differ from those of other volcanos and lead to this distribution of vents remains unclear. An alternative hypothesis for the morphology of Galapagos volcanos is that it reflects the pattern of intrusion of magma within the volcano. In essence, magma intruded into the volcano inflates the central part, pushing the summit region upward and steepening the slopes on the upper flanks. Another unusual characteristic of the western Galapagos volcanoes is the large size of their calderas, particularly in comparison to the size of the volcano.
Calderas form as a result of collapse of an underlying magma chamber.
A partial collapse of the caldera on Fernandina occurred in 1968, when the northern part of the caldera floor dropped 200 meters. Collapse occurred several weeks after a brief eruption. It was observed from a distance and scientists arrived shortly after the event, so that this is one of the best documented examples of a caldera collapse. Once formed, caldera may broaden as parts of caldera wall collapse. This occurred on Fernandina in 1988.