THE USE OF AVIRIS IMAGERY TO ASSESS CLAY MINERALOGY AND DEBRIS-FLOW POTENTIAL IN CATARACT CANYON, UTAH

The purpose of this research is to assess debris-flow potential in the area immediately surrounding Cataract Canyon, Utah. Analysis of shale samples from across the Colorado Plateau reveals that debris-flow occurrence in this physiographic province is inversely correlated with the smectite clay content of shale units and promoted by the presence of shales containing a high percentage of kaolinite and illite clays. This relationship between clays and debris-flow activity indicates that the nature of surface materials plays a large role in the initiation of debris flows. Surface materials in Cataract Canyon and vicinity have been mapped using hyperspectral imagery. AVIRIS data consisting of two approximately northeast-southwest trending flight lines was collected on November 9, 2001. The AVIRIS images obtained have been geometrically rectified, atmospherically corrected and classified using an artificial neural network. Field trips were made to the area in 2001, 2003 and 2004 to collect field spectra and surface samples. Both laboratory reflection spectra and semi-quantitative x-ray diffraction have been preformed on surface samples. Comparison of laboratory reflection spectra to AVIRIS spectra reveals that debris-flow deposits and colluvium in Cataract Canyon display the double-absorption feature characteristic of kaolinite at 2.2 µm. This kaolinite spectral signature is most pronounced in colluvial wedge samples and also appears in field and lab spectra of shale units in and around Cataract Canyon. Reflection spectra of debris-flow matrix samples in Cataract Canyon show that the clays in these materials are dominated by kaolinite and illite and lacking in montmorillonite. Semi-quantitative x-ray diffraction results show that both debris-flow and colluvial deposits in this area have similar clay mineralogies. Surface material maps have been derived from the AVIRIS data. These maps compare favorably to existing geologic data for Cataract Canyon, providing evidence for the feasibility of using AVIRIS data in geologic hazard assessment. Future work on this project will involve development of a debris-flow hazard map for Cataract Canyon which will integrate the AVIRIS-derived surface material data with existing data on Cataract Canyon’s topography, rainfall and drainage basin characteristics.