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ABSTRACT: Significance of Major Landslides on the Hawaiian Ridge

James G. Moore, W. R. Normark

A longstanding controversy on the role of large landslides in shaping Hawaiian volcanoes began when an investigator proposed that prominent sea cliffs on some of the islands owed their origin to faulting rather than marine erosion. In recent years, this debate has continued over the relative importance of downslope movement versus magmatic processes in the genesis of structural features of the volcanoes.

Data from recent side-looking sonar surveys (GLORIA) demonstrate that both the size and number of submarine landslides on the flanks of the Hawaiian Ridge are much greater than previously known. In fact, large-scale landsliding is so common that it is an integral part of the ridge's development. About 100,000 km2, half of the ridge's surface area from Kauai to Hawaii, has been modified by 17 large newly documented landslides, and other slides are undoubtedly covered by younger volcanic and slide material. Some slides are more than 200 km long, about 5000 km3 in volume, and rank among Earth's largest. Other data from recent surveys show additional large landslides northwest of Kauai, although increasing age away from the hotspot renders their details more obscure. Downslope movement modifies the subaerially exposed structural features of some volcanoes, such as the position of volcanic rift zones, and explains the enigmatic geometry of certain fault systems. Active slumps apparently are responsible for much of the current seismicity along the ridge and sometimes trigger eruptive activity. Prehistoric, rapidly emplaced, giant debris avalanches are believed to have produced tsunamis that deposited boulder-gravel beds hundreds of meters above sea level. The large landslides seem to culminate at the rapid shield-building stage of volcano development when eruption rates are about 0.1 km3/yr. The recurrence interval of sliding is long, from 103 to l05 years, because of the large ratio of (landslide volume)/(eruption rate . Because large landslides have also been identified at other marine volcanoes rising from abyssal depths, and their effects may be catastrophic, a survey of landslide-prone marine volcanoes should be initiated.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990