The island of Hawaii began to form some 800,000 years ago from the eruptions of giant volcanoes, of which Kilauea is the most active. Flows of lava from the volcanoes have heaped atop sediments that built up ages before on the sea bottom. Analysis of an earthquake that occurred in June 1989 indicates that the east side of Kilauea is slipping seaward, lubricated by the buried sediments, six miles below, on which the bottom of the volcano rests.

Studies of the underwater debris fields tell much about the islands' geological past and future. The current surveys are being carried out as part of the effort by the United States to map its entire exclusive economic zone, extending 200 nautical miles off all its shores. Recent findings, analyzed by Dr. James G. Moore, a specialist in Hawaiian volcanism, and five colleagues at the United States Geological Survey, have been published in The Journal of Geophysical Research.

Preliminary results have come from a British sonar system known as Gloria, and surveys now under way by American researchers. Gloria can map a 60-mile-wide swath of sea floor on a single pass. It was towed behind the British research vessel Farnella, which docked a few weeks ago in Honolulu. The survey was jointly sponsored by the Institute of Oceanographic Sciences in Britain and the United States Geological Survey. A 2,300-Foot Wave

The Americans are concentrating on recent landslides from the island of Hawaii, using multibeam sonars that can map the bottom more precisely than the Gloria system. This has produced a perspective diagram of one slide from the west coast of Hawaii and a survey of another that has slipped into the sea from Kilauea.

Geologists have identified two distinct processes whereby the Hawaiian Islands have shed land: slow slumping and catastrophic landslides. The Nuuanu landslide that swept away the northeast side of Oahu is thought to have been of the later type.

So great was its momentum that it crossed the Hawaiian Deep, 15,000 feet below sea level and moved up the slope beyond to 1,000 feet above the deep. The Hawaiian Deep is sea floor depressed by the enormous weight of the volcanoes.

Nearer shore is a giant amphitheater, now submerged, but presumably above water when the slide occurred. The island, as it aged and moved away from the "hot spot," has sunk 1,000 feet.