The morphology of Sierra Negra is the upturned soup bowl shape of the other Isabela volcanoes, however it does not have the steep sloping sides that are on others. Instead the slope goes from approximately 2 degrees at its base and although increasing averages only 5 degrees. The volcano has the largest caldera of all of the Galapagos volcanoes, with dimensions of 7.2 x 9.3 km, with the long axis being south west to north east. The caldera is also the shallowest of the Isabela volcanoes at only 100m. The caldera is structurally complex with a 14 km long ridge within it. A large fumarolic area, Volcan de Azufre, lies between this ridge and the western caldera wall. This fumarolic area is one of the locations where terrestrial sulfur flows have been identified, this is associated with the melting of sulfur deposits.