MAPPING THE OCEAN FLOOR

Early Mapping

With the development of sonar in World War II, a means was provided for studying the contour of the land underneath the oceans. Before sonar, the configuration of the ocean floor was mapped by a crude tracing method. A weight on a long chain or cable was lowered from a ship until the weight hit bottom. The depth of water at that point was determined. Then the weight was dragged slowly to show how the depths changed from place to place. Very deep oceans, strong

INTERNATIONAL GEOPHYSICAL YEAR

The International Council of Scientific Unions declared July 1957-December 1958 the International Geophysical Year (IGY), The council acted on the suggestion of American physicist Lloyd V. Berkner, who made a more modest proposal that the period be designated the third International Polar Year (the previous two had been 1882-1883 and 1932-1933). Timing was appropriate because IGY coincided with a time of unusual solar activity that could be observed with unprecedented accuracy.

U.S. scientists cooperated with colleagues world-wide to establish observation stations that collected and shared data in the fields of meteorology, geomagnetism, the aurora, the airglow, cosmic rays, ionospheric physics, latitude and longtitude determination, glaciology, and oceanography. An innovation of IGY data collection was the use of satellites and high-altitude weather balloons to collect data in the upper atmosphere. The Soviet Sputnik I was launched in October 1957 during IGY. By August 1958 the U.S. had four satellites in orbit and the U.S.S.R. had three. IGY projects showed that Earth's atmosphere extended further out into space than scientists had suspected and that there is a layer of atmosphere that contains high-energy electrons.

Source:

Trevor Illytd Williams, Science: A History of Discovery in the Twentieth Century (Oxford & New York: Oxford University Press, 1990).

currents, and turbulent seas limited the usefulness of this method.

Sonar

With sonar the picture is much clearer. As a ship moves along it can bounce sound waves down to the ocean floor. The reflection of the sound waves indicates the depth of the water and the shape of the bottom. Ships using sonar can move continuously, covering larger and deeper areas than with the tracing method.

Discoveries

Oceanographers were astonished by the immense volcanoes and canyons they found in the Pacific Ocean. East of the Tonga Islands (where Captain Bligh and Fletcher Christian parted company in Mutiny on the Bounty) lies a canyon seven miles deep—seven times the depth of the Grand Canyon. This Tonga-Kermadec Trench is but one of several canyons in the central Pacific Ocean. Some are two thousand miles in length, two-thirds the length of the United States; many are very narrow but extremely long and deep.

Volcanoes

There are also underwater volcanoes surrounding the Tonga-Kermadec Trench, one of which rises twenty-seven thousand feet above the sea floor (but still the tip is twelve hundred feet below the surface of the water). This underwater volcano is one of the highest mountains on earth.

Underwater World

The many deep trenches in the Pacific have common characteristics: they are about the same maximum depth (thirty-five thousand to forty thousand feet); they seem to have a V shape, with one side of the V more gently sloping and the other side more abrupt. Shallower trenches tend to have a U shape. Another characteristic of the trench regions is earthquake activity. Some of the most powerful earthquakes on the planet occur under water. Along with the quakes come the volcanoes. Many of the volcanoes have flattened tops, suggesting that they once rose above water and had their tops flattened by the action of pounding surf.