HESS, HARRY H. 1906-1969

Geologist

Hess's Theory

The plate tectonics theory, basic to oceanography and geology today, was accepted because of the work of Harry H. Hess on seafloor spreading. Once seafloor spreading was shown to occur, Hess concluded that continents drift over time, the result of continental plates of the Earth's crust moving laterally around the planet. This is the theory of plate tectonics, which was developed over a period of some fifty years.

Continental Drift

German scientist and explorer Alfred L. Wegener first proposed continental displacement (or drift) in 1924 to explain how various parts of the continents seemed to fit into each other like pieces of a jigsaw puzzle. He thought they were all connected once and drifted apart, but he could not prove his theory.

Midocean Ridges

Then the midocean ridges were found. When Harry Hess was a navy captain of a Pacific attack transport, he was intrigued by flat-topped mountains under water identified by his sonar equipment. Hess named these mountains guyots, after Arnold Guyot, a Swiss-American who was Princeton's first professor of geology. In the 1950s guyots were found to be part of the Earth's mantle just below the surface. The mantle moves up in the ridges and pushes the seabed to either side. Hess said it eventually moved under the continents, pushing them apart. Hess published this theory in a 1960 report to the Office of Naval Research. His 1962 book History of the Ocean Basins explains his ideas in more detail.

Hess Explains the Guyots

Hess determined these guyots were volcanic islands formed along the midocean ridges. Since the peaks were submerged, water quickly (geologically speaking) eroded the cone peaks to form flat-topped mountains. The farther these were from the ridge, the deeper they were under water and the more eroded they became, so they must have moved away from their place of origination over time. This could only happen if new mantle were rising to push the guyots aside.

The First Continent

Hess proposed an early single land mass named Pangaea that broke into continental plates, which are now recognized as the continental land masses. The plates moved apart by seafloor spreading. Hess's ideas suggested the reversals of the magnetic poles should be symmetrical along the ocean ridges, a phenomenon demonstrated by British researchers in 1963.

Source:

H. W. Menard, "The Deep-Ocean Floor," Scientific American, 221 (September 1969): 126-142.

Hess, Harry Hammond (1906–69) An American geophysicist from Princeton University, Hess made important contributions to the theory of plate tectonics. He devised the concept of sea-floor spreading (see also DIETZ, ROBERT SINCLAIR), and discovered and named guyots. His Essay in Geopoetry (1960, 1962) was an attempt to link the features of the sea floor in a common hypothesis, in which he proposed that the continents move passively on rafts or rigid plates.