San Cristobal Island is one of the oldest Galapagos Islands where the flora and fauna has taken over and been exposed to the elements.  This island is no longer an active volcano as it sits in the southeastern end of the archipelago. Now this island is slowly deteriorating to the point that it will go back into the ocean.  The Galapagos Islands are formed because of the activity of a stationary “hot spot” that lays on the northwestern end of the archipelago under the Nazca Plate.  This tectonic plate slides towards the southeast and as it goes by the “hot spot” area it produces enormous volcanoes that when they emerge out of the ocean become islands.  The islands that had been carried away from the “hot spot” area then became extinct volcanoes.