USING IMMERSIVE TECHNOLOGY TO MAP PRE- AND POST- FAILURE MORPHOLOGY OF THE ANDY GUMP LANDSLIDE: GRAND MESA, COLORADO, USA

Engineering geomorphologists use fundamental knowledge of processes to explain past and present conditions and to provide a prediction of the future. This approach when dealing with past through present conditions, encourages uncertainty because of a lack of ability to measure of the past landscape. Thus, we developed a methodology, using immersive technology, to reconstruct a slope prior to failure and to show movement through time. This method facilitates measurement of slope geometry, pre- and post-movement, and simulation of landslide movement. Knowing the geometry of the slope both pre-and post-failure is fundamental to understanding geomorphological parameters, such as morphology, movement mechanics, and triggering mechanisms, which are essential to study a landslide for predicting future movement.

The southern facing slopes of Grand Mesa Steep consist of consolidated deposits of weathered volcanics, clays, and sandstones and are predisposed to movement. During the summer of 2005, heavy rainfall triggered a landslide; locals refer to it as the Andy Gump Landslide.

We collected coordinates and elevations of 3,000 points on the landslide surface. We also mapped the surrounding terrain, the surface of the landslide, the soil depth, and collected samples of failed and in situ soil and rock for laboratory testing. These elevation data were interpolated and used to develop a slope failed surface. This surface was subtracted from the Digital Elevation Model (DEM), representing the terrain before the occurrence of the landslide to determine the depth and volume of mass that was moved and deposited.

The landslide is ~380 m long and ~65 m wide and incorporated more than 10 m depth of regolith. Precision surveying of the adjacent slope and the current slide surface shows a slight change in slope from 20° to 15°; ~59,000m³ of debris was transported as the landslide. The overall morphology of the slope before and after the failure indicates that the landslide is rotational in nature. Several large blocks of rock-soil debris remained intact as the landslide mobilized. We used these blocks as tag points in the dynamic visualization of the landslide. ESRI ArcGIS^® was used in conjunction with a SEOS^® system to perform the dynamic immersive visualization. This visual approach provides an important tool to assess landslide mechanics and demonstrate how change occurred.