The Galapagos Islands are a series of gigantic volcanic peaks composed almost exclusively of basalt giving the islands their dark gray color. They lie where the Nazca Plate passes under the South American Plate in an area of great geologic activity. Eruptions have taken place in historical times on Fernandina, Isabela, Pinta, Marchena, Santiago and Floreana.
Most of the islands have the classic cone shape of a " Shield Volcano " created from the build up of layers of lava. These volcanoes have risen from 6500 to almost 10,000 ft (2000-3000 m) above the seabed. The other islands appear like a tilted tabletop and were created from Volcanic Plateaus. Plateaus are created when the eruption of basalt lava poured quickly from fissures rather than central vents.

A study of geology in action, the Galapagos Islands is one of the world's most active volcanic areas, with more than 50 eruptions in the past 200 years.