The birth of a volcanic island is an event marked by prolonged and violent travail: the forces of the earth striving to create, and all the forces of the sea opposing. At the place where the formation of such an island begins, the sea floor is probably nowhere more than about fifty miles thick. In it are deep cracks and fissures, the results of unequal cooling and shrinkage in past ages. Along such lines of weakness the molten lava from the earth’s interior presses up and finally bursts forth into the sea. But a submarine volcano is different from a terrestrial eruption, where the lava, molten rocks, and gases are hurled into the air from an open crater. Here on the bottom of the ocean the volcano has resisting it all the weight of the ocean water above it. Despite the immense pressure of, it may be, two or three miles of sea water, the new volcanic cone builds upwards towards the surface, in flow after flow of lava. Once within reach of the waves, its soft ash is violently attacked by the motion of the water which continually washes away its upper surface, so that for a long period the potential island may remain submerged. But eventually, in new eruptions, the cone is pushed up into the air, where the lava hardens and forms a rampart against the attacks of the waves.
