APPLICATION OF STEREO 3-D IMAGERY FOR INTERPRETATION OF LANDSLIDES, FAULTING, GEOLOGIC STRUCTURES AND GEOMORPHIC FEATURES

Stereo 3-D (S3-D) digital images (anaglyph glasses required), together with traditional tools, allows fresh new terrain interpretations. Manipulating scale, relief, digital shading (four are available), sun angle, viewing direction and image tilt , etc. produces differing views of the same terrain -- aiding in identifying, tracing, and interpreting surface anomalies. These methods were used to identify landslides, landslide-prone slopes, faults and potential water well sites. Terrains studied or reviewed included Cascade volcanic rocks, granitic rocks, meta-sediments, and the Cascadia subduction zone.

Near-surface water circulation can be evaluated by use of three tools of this digital program:

1. Watershed Definition which gives a measure of Upslope Surface Area at any location,
2. Divide Boundary which gives a quick delineation of catchments, and

3. Horton Overland Flow which displays a runoff network.

These tools are used to estimate the water flux at the heads of landslides or to locate and define the recharge potential of water wells. Geologic mapping and spring locations are combined with the S3D tracing of fault lineaments to target well sites in bedrock permeability. Imagery clearly defines landforms and active and inactive faults which have topographic expression.

S3D examples delineate slope angles, ‘patterns’, etc. of debris slide sites/terrain using a specific “digital shading”. Slope shadings define potential failure sites by producing maps colored in four classes keyed to field derived slope parameters, e.g., slope angles, offset features, etc. Examples include color bands (degrees) of landslide topography and offset slump blocks.

Large posters for identifying unusual/special terrain features are shown. These examples demonstrate how this innovative approach can be used to highlight a variety of landform elements which may be subtle, or not even visible, on standard shaded relief images and even air photos. Images are Lidar-derived (1-2 meters) and USGS 10 meters, 30 meter DEM‘s.