Location of the Debeque Canyon landslide.
Lateral deflection at landslide toe during the April 1998 activation has bent the guardrail along I-70 westbound lanes. The photographer is standing on the landslide toe, which moved toward the river. Photo courtesy of CDOT.
Total vertical heave of 14 feet in April of 1998. The vertical heaving of the toe required continuous fill placement by CDOT Maintenance to keep highway open during duration of landslide movement. Photo courtesy of CDOT.
In response to the 1998 event and the perception of possible future catastrophic events, the Federal Highway Administration funded a multi-agency team of geologists and engineers to investigate, map, analyze, monitor, and design mitigation concepts for Interstate 70 where it crosses the toe of the landslide. The team, administered and managed by CDOT Geotechnical Unit, includes the Colorado Geological Survey (CGS), Golder Associates, Inc., Colorado School of Mines (CSM), and the United States Geological Survey (USGS).
The geologic work consisted of photogrammetric geologic mapping, stratigraphic measurements, cross section construction, literature and history research, relative age dating, instrumentation installation, and digital photogrammetric analysis of early aerial photography. The engineering work consisted of subsurface investigation, materials testing, engineering analyses, preliminary mitigation designs, hosting a technical workshop and creation of the final technical report.
The investigation indicates that the DeBeque Canyon Landslide developed during the Late Pleistocene due to fissuring along pre-existing shear zones and prominent jointing, in response to downcutting of the Colorado River. The downcutting exposed thick, weak shale beds that later failed, creating the bulk of the central Rubble Zone. The landslide is continuously active and in a state of perpetual creep. The current assessment is that a catastrophic failure is unlikely at this time. The postulated slide mechanism is much like a conveyor belt, as shown in the illustration below (courtesy of Golder Associates, Inc.) This figure is not to scale.
The DeBeque Canyon Landslide is currently instrumented with tools that include two automatic base stations using cellular communication that monitor tiltmeters, extensometers, inclinometers, a rainfall gauge, and rockfall warning fences. Also included are arrays of mounted survey prisms and GPS points, manually read inclinometers and extensometers, and portable peizometer data loggers at boring locations. The CGS, with assistance by the USGS, is currently monitoring the instruments.
Geologic Map of the DeBeque Canyon Landslide. Geologic mapping by Jon White (CGS) and Jerry Higgins (CSM).
Oblique 3-D view of a Digital Elevation Model (DEM) with draped 1999 aerial photography. Colored lines are along cross section C through the main rotational area. Where lines disappear or are not shown, the 1999 ground elevation is higher than previous years. The cross section shows that the landslide has moved several times since 1950. Cross section lines were plotted from digital photogrammetric analyses of earlier aerial photography by USGS. Image generated by Matt Morgan and Jon White.