The Birth of an Island
MILLIONS OF YEARS AGO, a volcano built a mountain on the floor of the Atlantic. In eruption after eruption, it pushed up a great pile of volcanic rock, until it had accumulated a mass a hundred miles across at its base, reaching upward toward the surface of the sea. Finally its cone emerged as an island with an area of about 200 square miles. Thousands of years passed, and thousands of thousands. Eventually the waves of the Atlantic cut down the cone and reduced it to a shoal—all of it, that is, but a small fragment which remained above water. This fragment we know as Bermuda.
With variations, the life story of Bermuda has been repeated by almost every one of the islands that interrupt the watery expanses of the oceans far from land. For these isolated islands in the sea are fundamentally different from the continents. The major land masses and the ocean basins are today much as they have been throughout the greater part of geologic time. But islands are ephemeral, created today, destroyed tomorrow. With few exceptions, they are the result of the violent, explosive, earth-shaking eruptions of submarine volcanoes, working perhaps for millions of years to achieve their end. It is one of the paradoxes in the ways of earth and sea that a process seemingly so destructive, so catastrophic in nature, can result in an act of creation.
Islands have always fascinated the human mind. Perhaps it is the instinctive response of man, the land animal, welcoming a brief intrusion of earth in the vast, overwhelming expanse of sea. Here in a great ocean basin, a thousand miles from the nearest continent, with miles of water under our vessel, we come upon an island. Our imaginations can follow its slopes down through darkening waters to where it rests on the sea floor. We wonder why and how it arose here in the midst of the ocean.
The birth of a volcanic island is an event marked by prolonged and violent travaiclass="underline" the forces of the earth striving to create, and all the forces of the sea opposing. The sea floors where an island begins, is probably nowhere more than about fifty miles thick—a thin covering over the vast bulk of the earth. 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, gases, and other ejecta are hurled into the air through 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 upward toward the surface, in flow after flow of lava. Once within reach of the waves, its soft ash and tuff are violently attacked, and for a long period the potential island may remain a shoal, unable to emerge. But, eventually, in new eruptions, the cone is pushed up into the air and a rampart against the attacks of the waves is built of hardened lava.
Navigators’ charts are marked with numerous, recently discovered submarine mountains. Many of these are the submerged remnants of the islands of a geologic yesterday. The same charts show islands that emerged from the sea at least fifty million years ago, and others that arose within our own memory. Among the undersea mountains marked on the charts may be the islands of tomorrow, which at this moment are forming, unseen, on the floor of the ocean and are growing upward toward its surface.
For the sea is by no means done with submarine eruptions; they occur fairly commonly, sometimes detected only by instruments, sometimes obvious to the most casual observer. Ships in volcanic zones may suddenly find themselves in violently disturbed water. There are heavy discharges of steam. The sea appears to bubble or boil in a furious turbulence. Fountains spring from its surface. Floating up from the deep, hidden places of the actual eruption come the bodies of fishes and other deep-sea creatures, and quantities of volcanic ash and pumice.
One of the youngest of the large volcanic islands of the world is Ascension in the South Atlantic. During the Second World War the American airmen sang
this island being the only piece of dry land between the hump of Brazil and the bulge of Africa. It is a forbidding mass of cinders, in which the vents of no less than forty extinct volcanoes can be counted. It has not always been so barren, for its slopes have yielded the fossil remains of trees. What happened to the forests no one knows; the first men to explore the island, about the year 1500, found it treeless, and today it has no natural greenness except on its highest peak, known as Green Mountain.
In modern times we have never seen the birth of an island as large as Ascension. But now and then there is a report of a small island appearing where none was before. Perhaps a month, a year, five years later, the island has disappeared into the sea again. These are the little, stillborn islands, doomed to only a brief emergence above the sea.
About 1830 such an island suddenly appeared in the Mediterranean between Sicily and the coast of Africa, rising from 100-fathom depths after there had been signs of volcanic activity in the area. It was little more than a black cinder pile, perhaps 200 feet high. Waves, wind, and rain attacked it. Its soft and porous materials were easily eroded; its substance was rapidly eaten away and it sank beneath the sea. Now it is a shoal, marked on the charts as Graham’s Reef.
Falcon Island, the tip of a volcano projecting above the Pacific nearly two thousand miles east of Australia, suddenly disappeared in 1913. Thirteen years later, after violent eruptions in the vicinity, it as suddenly rose again above the surface and remained as a physical bit of the British Empire until 1949. Then it was reported by the Colonial Under Secretary to be missing again.
Almost from the moment of its creation, a volcanic island is foredoomed to destruction. It has in itself the seeds of its own dissolution, for new explosions, or landslides of the soft soil, may violently accelerate its disintegration. Whether the destruction of an island comes quickly or only after long ages of geologic time may also depend on external forces: the rains that wear away the loftiest of land mountains, the sea, and even man himself.
South Trinidad, or in the Portuguese spelling, ‘Ilha Trinidade,’ is an example of an island that has been sculptured into bizarre forms through centuries of weathering—an island in which the signs of dissolution are clearly apparent. This group of volcanic peaks lies in the open Atlantic, about a thousand miles northeast of Rio de Janeiro. E. F. Knight wrote in 1907 that Trinidad ‘is rotten throughout, its substance has been disintegrated by volcanic fires and by the action of water, so that it is everywhere tumbling to pieces.’ During an interval of nine years between Knight’s visits, a whole mountainside had collapsed in a great landslide of broken rocks and volcanic debris.
Sometimes the disintegration takes abrupt and violent form. The greatest explosion of historic time and the literal evisceration of the island of Krakatoa. In 1680 there had been a premonitory eruption of this small island in Sunda Strait, between Java and Sumatra in the Netherlands Indies. Two hundred years later there had been a series of earthquakes. In the spring of 1883, smoke and steam began to ascend from fissures in the volcanic cone. The ground became noticeably warm, and warning rumblings and hissings came from the volcano. Then, on 27 August, Krakatoa literally exploded. In an appalling series of eruptions, that lasted two days, the whole northern half of the cone was carried away. The sudden inrush of ocean water added the fury of superheated stream to the cauldron. When the inferno of white-hot lava, molten rock, steam, and smoke had finally subsided, the island that had stood 1400 feet above the sea had become a cavity a thousand feet below sea level. Only along one edge of the former crater did a remnant of the island remain.