USE OF HYPERSPECTRAL AVIRIS IMAGERY IN IDENTIFYING LANDSLIDE-PRONE AREAS IN RECENT VOLCANIGENIC SOILS

Identification of areas prone to catastrophic slope failure prior to any construction activities has long been the goal of both engineers and engineering geologists. Presently, landslide hazard maps developed by state and municipal governments have been largely based upon knowledge of soils gained from actual site testing and/or by combining such information with slope and structural geology data. While this has generally been found to be effective, it must always be realized that failure of slopes is a multivariate phenomenon and other factors can significantly influence slope stability. In recent years, for example, it has been shown that the cause of some slides occurring on slopes underlain by pyroclastic debris can be traced to the saturation of soils dominated by the mineral allophane. Unlike most clay minerals, identification of allophane cannot be easily accomplished using X-ray diffraction (this, because the mineral is generally considered as "amorphous" and possesses only short-term order). Rather, its identity requires infrared spectrographic analysis and/or the examination of SEM photographs. The latter is especially definitive because the mineral occurs typically as spherical particles having a diameter of approximately 25 microns. Because the mineral can be identified by its infrared signature, the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) can also be employed to identify sites where the mineral occurs as a dominant soil constituent. By combining AVIRIS imagery showing the distribution of this mineral with rainfall data, slope values, degree of vegetative cover, and earthquake epicenter distances using the GIS program ArcView®, maps can be constructed that identify sites that would be most susceptible to slope failure.