Where are there Extinct Volcanoes under the sea?
Coral atolls are thought to be the coral-covered tops of extinct volcanoes. In ‘The Voyage of the Beagle’ Charles Darwin brilliantly anticipated the theory of continental drift and sea-floor spreading by observing that in the Pacific there are frequently found a line of coral reefs at one end of which is either an extinct volcanic island or an active one. He postulated that the sea-floor was moving, and that the periods of vulcanicity were cyclic. After each volcanic eruption, the moving sea-floor carried a newly-formed island away from the hot-spot, and the island sank, leaving a slowly-decending summit which was colonised by corals. As this continued to sink with the remains of the volcano, a living reef was left at or near sea-level on an ever-growing foundation of dead coral. In some cases the rate of sinking (or of sea-level rise) is too great for the growth of coral to keep pace. Then the extinct volcano (perhaps with a capping of dead coral) sinks below the surface and becomes a
