Debeque Canyon Landslide

The Debeque Canyon Landslide

Introduction
The DeBeque Canyon Landslide is a major landslide complex in western Colorado that has historically impacted the east-west highway and railway corridor on the Colorado River. Three significant reactivations or ground movements have occurred during the past century. The precise date of the first major movement is unknown but occurred in the late 1890s or early 1900s. That slide movement was the largest and reportedly shifted the river channel and damaged railroad facilities on the north bank of the Colorado River. The second noteworthy movement occurred in February 1958 when the roadway was widened for a modern two-lane highway. The widening resulted in further cutting and destabilizing of the landslide toe, with subsequent movements resulting in the heaving of the roadway 23 vertical feet. In April 1998, the third major movement occurred and caused Interstate 70, constructed in the mid-1980s, to heave 14 vertical feet. The highway also shifted 5 to 6 feet laterally towards the river during this event. It was only by the rapid response of the Colorado Department of Transportation (CDOT) that Interstate 70 was not completely closed and the only major east-west interstate corridor in Colorado blocked.

Photo taken in 1910 of DeBeque Canyon landslide. View is to the north. Note toe of landslide extending into the Colorado River. There is little reworking by the river of the landslide toe, suggesting very recent emplacement. Note railroad and old stagecoach road on north bank. Photo courtesy of the Julia Harris Collection at the Museum of Western Colorado, Grand Junction.

Photo taken during pavement rupture in the westbound lanes near median at beginning of April 1998 movement. CDOT Maintenance staff was on site at time of initial rupture and prevented vehicles from hitting the damaged, uplifted section of road. Photo courtesy of CDOT.

View to the southeast showing delineated morphologic divisions of the DeBeque Canyon Landslide. The DeBeque Plateau is above the landslide. The repaired segment of Interstate 70 crosses the landslide toe on the south bank of the Colorado River. Photo by Jon White.

View to the northeast of major fissures of the DeBeque Canyon Landslide. Fissures separate a headwall of intact Mesa Verde Formation on right side from the displaced Upper Block to the left. Photo by Jon White.

Oblique aerial photo showing the Upper Block, the Disturbed West Block, and the upper portion of the Rubble Zone below the active cliff face. Note open fissuring in the Upper Block and its proximity to Interstate 70 and the Colorado River. View is to the southwest. Photo by Jon White.

View to the southwest of the Rubble Zone. The larger sandstone blocks are the size of houses. Note morphology closer to the Interstate where arcuate concave areas mark intermediate scarps. Rotational downward movements deflated the Rubble Zone at both the East and Main rotational areas and vertically elevated the landslide toe, significantly damaging the roadway in 1958 and 1998. Photo by Jon White.

Last Updated: 12/9/2010 10:10 PM

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.

Investigations
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.

Current Research
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.