The Galapagos IslandsThe Galapagos Islands lie on the northern edge of the Nazca plate, which is crawling southeast and subducting underneath the South American plate, forming the Andes Mountains. When the subducted Nazca plate reaches the asthenosphere (about sixty miles below), it melts and forms magma. The comparably lighter magma rises between cracks in the crust and accumulates near the surface. In the area below the Galapagos, a hot spot formed where the magma was pushed above the crust and the Galapagos volcanoes subsequently formed. The volcanoes on the Marchena, Pinta, and Tower islands are currently active and contain an abundance of intriguing information. The Wolf and Darwin islands to the northwest of the three larger islands are eroded volcanoes that are now extinct. Many of the volcanoes of the Galapagos, with the northern islands being no exception, are classified as shield volcanoes. Shield volcanoes are identifiable by their gentle slopes and flat coastline. They regenerate through lava flows, which pour out of a central vent creating its warrior shield profile, hence the name. The lava flows thin out by spreading over a large area and years of accumulation of thin layers yields a shield volcano. Some of the northern islands also exhibit calderas, which should not be confused with a crater. Calderas can be large, and form when magma is withdrawn from an underground reservoir beneath the volcano. This leads to a partial collapse of the overlying ground and consequently a large depression.
The Galapagos are well known to be home to many endemic species of animals and plants, such as the giant tortoise, the scalesia and miconia, the Galápagos penguin, and the flightless cormorant.