Pinnacle Rock looms under a brooding sky off the Galápagos’ Bartolome Island. The island’s most famous feature (it even got airtime in the movie, Master and Commander ) is actually an eroded lava formation called a tuff cone. When hot lava from a now-extinct volcano on land reached the sea, the temperature difference caused explosions, producing thousands of thin layers of basalt ash that eventually formed into this towering monument.

(Photograph shot on assignment for, but not published in, the National Geographic book Majestic Island Worlds, 1986)