Cerro Azul volcano occupies the southwest corner of Isla Isabela (Albermarle Island). Although smaller than it neighbor to the west, Sierra Negra, at 1690 m (5541 feet) its summit is higher. Cerro Azul is quite active, with 9 known historic eruptions, the most recent of which began in Sept, 1998 and has continued into October (updated information about this eruption can be found on the Galapagos News page). That eruption was somewhat unusual because lava erupted both from a vent near the eastern base and from a vent within the caldera. Because of its remoteness, it is likely that many eruptions over the last several hundred years have gone unnoticed. The composition of Cerro Azul's lavas is quite uniform and rather similar to that of Sierra Negra's. Both Cerro Azul and Sierra Negra have strong enrichments in incompatible elements, indications that these melts are derived primarily from the Galapagos mantle plume rather than entrained asthenosphere.