CHARACTERIZATION OF MASS WASTING THROUGH THE SPECTRAL ANALYSIS OF LIDAR IMAGERY: OWYHEE RIVER, SE OREGON

Large landslides can affect adjacent channels at time scales on the order of 10⁴ years with a range of impacts specific to landslide character. Quantifying landslide character is therefore an important step in understanding hillslope-channel interactions. The Owyhee River of southeastern Oregon has many reaches dominated by mass wasting events. The main factor in landslide generation along the Owyhee River is a lithologic contact where relatively soft or weak sediments are mantled by a coherent basaltic caprock. Most landslide failure surfaces originate in the underlying weak sediments. There are three main styles of mass wasting along the Owyhee River: earth flows, rotational landslides, and rock falls. The earth flows are dominated by fine sediment. The rotational landslides are composed of large coherent blocks of the basalt caprock and surrounded by finer sediments from the underlying units. Large cantilevering columns of basalt mark the rock falls with little or no evidence of the underlying fine sediments.

Spectral analysis of high-resolution Digital Elevation Models (DEM), obtained from LiDAR (Light Detection and Ranging) imagery, was carried out following methods described by Booth et al. (2009) to determine the characteristic spectral signature inherent in each style of mass wasting. Two-dimensional discrete Fourier transforms of the failed terrain, normalized by comparison with a synthetic topography, highlight the characteristic spectral power for each type of landslide. The rotational landslides are dominated by large wavelength features, while the block fields from rock falls are dominated by short wavelengths superimposed on large wavelength landforms. A sequence of adjacent, similar rotational landslides of different ages allowed us to observe changes in spectral power distribution through time. We hypothesized that short wavelength features become less pronounced over time as erosion and other processes work to dampen the smaller scale topography. Our long-term goal is to determine which landscape properties set the characteristic spectral signatures of the different styles of mass wasting identified in the Owyhee River region, and whether these signals are representative of mass wasting in regions with similar geology.