The Turnagain Heights Landslide, Anchorage, Alaska

During the Alaska earthquake of March 27, 1964, a large landslide, involving a strip of coastline about 8,500-ft long and extending inland about 900-ft, occurred in the Turnagain Heights area of Anchorage. Soil conditions in the slide area are described and an analysis of the mechanics of the landslide development is presented. It is concluded that the slide developed as a result of a loss in strength of the soils, particularly lenses of sand, underlying the slide area as a result of the sequence of earthquake ground motions, and that the mechanics of soil movement in the slide area were complex, involving the subsidence of large blocks of soli, the lateral displacement of clay in a 25-ft thick zone, and the simultaneous lateral translation of the slide debris on liquefied sands and silts. The relatively small margin separating the catastrophic failure, which developed from a possibly adequate performance under equally strong shaking, but of somewhat shorter duration, is noted and suggested as a basis for exercising great care in translating experiences of such failures to other areas and conditions.