Tom Evancho, age 12, of Indianapolis, Indiana, for his question:
Are there really volcanic mountains in the sea?
Earth scientists are taking a new look at volcanic activity in general. Evidence of both ancient and modern eruptions on the continents has been gathered for centuries. A few eruptions also have been noticed at sea, but detailed surveys now suggest that ocean volcanoes may outnumber those on the land.
We tend to regard a newsworthy volcanic eruption as a local catastrophe that brings disaster to the people of some near or distant land. Earth scientists now regard "land" eruptions as merely one part of a vast planetary picture of volcanic unrest. Certainly the seabed is as prone to eruptions as the continents, and it always has been. And this worldwide view calls for some larger ideas. Volcanic activity on land and at sea, it seems, has played a far greater role in shaping and reshaping the earth than we have supposed.
Since the 1500s, Ascension Island has been known as a treeless pile of cinders in the middle of the Atlantic. But fossilized forests are found there. Ascension's black cinders are volcanic ash and the island has four extinct volcanic vents. This bleak isle is the cone of a fairly recent marine volcano in the ocean. It erupted in 1913 and the little island disappeared below the waves. It reappeared after another eruption in 1920 only to disappear again after yet another eruption in 1949.
The geological history of Bermuda began with a series of eruptions in the Atlantic. Basalt lava and other volcanic debris piled up on the bed of the sea. The seething water spouted up in fountains carrying ashes, dead fish and bubbling gases. At last, the submarine volcano reached the surface. Its soft minerals were battered and bashed by pounding waves, but each eruption built it higher. When the cindery cone reached 1000 feet, the submarine volcano became extinct and the old fire mountain became quiet. Winds and rains wore down its cindery peak to the low lying island of Bermuda.
Most isolated ocean islands are built by submarine volcanoes. The bases of countless atolls are volcanic cones crusted with coral. Ocean charts show hundreds of extinct volcanoes below the surface. The world's bulkiest submarine volcanoes built a chain of islands hundreds of miles long. They are the wondrous Islands of Hawaii. The massive building job began millions of years ago on the deep floor of the Pacific. With each eruption, the volcanic peaks grew higher. At 14,000 feet, they broke the surface and became islands of dry land. The submarine volcanoes are still erupting, though their peaks now stand 30,000 feet above their bases on the ocean floor.
To us, a volcanic eruption can be a sudden disaster. But to the patient earth, it is a building operation. Volcanoes have added massive layers to the continents. However, the job of marine volcanoes is harder. In mid ocean, eruptions must push up against a tremendous weight of water that may be two or three miles deep. When these volcanic peaks reach the surface, pounding waves are waiting to wear them away. Many fail and remain submerged. Others erupt again and again and finally become islands of dry land.