The Great Islands Under The Sea

THE GREAT ISLANDS UNDER THE SEA continued

Sonar, the most important development for researching the topography of the
ocean, was in use experimentally before World War II and was brought to a
high degree of perfection during the period of naval action from the 1940s to
the 1960s. It is now possible to sketch in considerable detail the bottom of
the ocean: its mountains, rifts, plains and rises are being defined with greater
accuracy on marine charts as their depths from the surface are established at
different points through repeated consecutive soundings.

Sonar is a sound wave bounced off the bottom and calculated for depth measu-
rement until an operational mistake enhanced its effectiveness. This fortunate
oversight occurred in 1944 on a naval vessel in the central Pacific under the
overall command of Admiral Harry Hess. Sonar beamed at the bottom was
checked every half hour or so as a general control for surface vessels, except
in emergencies, such as the presence of submarines.

The fact that a sonar technitian forgot to turn off the sonar resulted, for the
first time, in a running record of the bottom, a practice later adopted by hydro-
graphic vessels researching a specific area.

This record of the rises and falls of the bottom in a fairly straight line revealed
the submarine presence of a series of flat-topped mountains, never before
noted as such, later referred to as guyots or seamounts. Many of these sea-
mounts in the Atlantic lie fairly close to the surface, as though they had once
been islands in an earlier and somewhat shallower ocean.