Characterization of Landslide Geometry and Motion near Black Canyon City, Arizona

Abstract:

Techniques in the assessment and mitigation of the landslide hazard can be strengthened with application of structure from motion (SfM)-- an inexpensive photogrammetric method. We investigate a landslide north of Black Canyon City, Arizona. The ~0.6 km² landslide is easily identified through remotely-sensed imagery and in the field. The landslide displaces series of Early and Middle Miocene volcanic and sedimentary rocks. We use SfM to generate a 0.2 m resolution digital elevation model and rectified ortho-mosaic from UAV- and balloon-based images. Derivative maps (hillshade, slope, contour) and the ortho-mosaic were used as base map for our detailed surface geomorphology and geology mapping. The main head scarp is ~600 m long and oriented NE-SW; minor scarps oriented NW-SE are also identified. Numerous open fractures (mm to m lengths) were identified throughout the landslide body (mostly with longitudinal orientation). The occurrence of a distinctive layer of reddish dark colored basalt lava presents a key displaced marker to estimate the landslide movement. Using this marker, the total displacement is estimated to be ~70 m vertically with maximum translation of ~95 m to the SE by both translation and horizontal axis rotation. The landslide geometry, fracture distribution and orientation, all indicate that the landslide is a rotational landslide with its surface movement is largely controlled by local topography. We estimate the rate of the slide motion by measuring the amount of fracture displacement and speculative ages of the disturbed vegetation located along the fractures. The analysis indicates a slow average landslide velocity of about 16 mm/year.