Numerous mega-landslides shed from the flanks of Hawaiian Island volcanoes are scattered across the sea-floor surrounding the islands. Bathymetric studies on the northeast side of the Kohala volcano has led to the recognition of a huge slope failure known as the Pololu landslide. Since 1988, however, various researchers have come to different conclusions as to the nature and size of the landslide.

Study of the contours of Kohala volcano's northeast subaerial flank provides critical evidence to understanding the Pololu landslide. Offset of contour trends on the volcanoe's northeast slope gives evidence that the slope is underlain by a landslide that extends from the volcano's summit to the coast. Furthermore, the offsets indicate that the surface of sliding is planar downslope from the head area and is less steep than the topographic surface.

Cross-sectional retro-deformation of the landslide mass, whereby the zone of depletion is re-filled with landslide material, shows the landslide displacement to be approximately 250 meters. Using this value and the principal of mass balance, the depth of the slide plane just downslope from the zone of depletion is calculated to be approximately 1 km.

From the various parameters determined by contour analysis and cross-section balancing, it is concluded that the slide plane daylights at the base of the 1000 meter high coastal cliffs at the base of the subaerial slope. Based on this daylight location, a logical conclusion is that the cliffs formed when the lower part of the landslide catastrophically moved offshore as a debris avalanche.

Furthermore, the location and geometry of the slide plane indicates that the landslide on Kohala volcanoe's subaerial slope cannot be part of the Pololu landslide as envisioned by previous researchers and must be a separate mega-landslide. The proposed name for this feature is the Kohala landslide. The overall analysis demonstrates the power of cross-section balancing for interpreting translational landslide geometries.

Dr. Kim Bishop, Professor of Engineering Geology at California State University, Los Angeles, California. Kim Bishop attended UCLA as an undergraduate and USC for his Ph.D., where he obtained degrees in Engineering Geology and Geology, respectively. He also has Master degrees from CSU Northridge (Civil Engineering) and CSU Los Angeles (Geology). He is a California PE, PG, and CEG. He worked for 8 years in engineering geology consulting before joining the faculty at CSULA, where he has taught engineering geology, structural geology, and tectonics courses for the past 22 years.