The Galápagos Islands are an isolated set of volcanoes, consisting of shield volcanoes and lava plateaus, located west of Ecuador. They are driven by the Galápagos hotspot, and are between 4.2 million and 700,000 years of age. The largest island, Isabela, consists of six coalesced shield volcanoes, each delineated by a large summit caldera. Española, the oldest island, and Fernandina, the youngest, are also shield volcanoes, as are most of the other islands in the chain. The Galápagos Islands are perched on a large lava plateau known as the Galápagos Platform, which creates a shallow-water depth of at the base of the islands, which stretch over a -long diameter. Since Charles Darwin's famous visit to the islands in 1835, over 60 recorded eruptions have occurred in the islands, from six different shield volcanoes. Of the 21 emergent volcanoes, 13 are considered active.