Safety Monitoring of Rock Slide at Yosemite National Park

SAFETY MONITORING OF ROCK SLIDE

In late April 2006, a major rock slide occurred burying the main highway access into California’s world-famous Yosemite National Park.

The slide blocked California’s State Highway 140 which is the main all year-round route to the Park, creating a number of major concerns for visitors and neighbouring communities.

What initially appeared to be a problem of a few rocks rolling onto the highway from the adjacent slope quickly turned into a complex rock slide with a volume of approximately 1.5 to 2.0 million cubic metres. The area created a number of concerns for public safety and significant implications for the local community of Mariposa.

Impacts included significant losses in business revenue due to limited park entry, traffic congestions to alternative park access routes as well as fears of inundation of infrastructure, homes, camping grounds and businesses.

With significant media coverage and public involvement, this event required the effort of a number of State Agencies and professionals to address the growing concerns of the public.

On the 12th June 2006, U.S. Geological Survey visited the area and concluded it would be difficult to define whether the slide mass was slowly creeping, accelerating, decelerating, or completely at rest.

GroundProbe’s Slope Stability Radar (SSR) was first deployed at Yosemite in June 2006. The system was set-up adjacent to the rock slide on the opposite side of the Merced River. Within an hour of deployment, the movement of the landslide was characterised, with faster and slower moving parts of the slide easily identified by the system’s real-time capabilities and sub-millimetre precision.

This gave the California Department of Transportation great confidence as it defined the stability of the area and progressed with workings to re-establish alternative access to the park. Today, the system continues to monitor the area and keeps the California Department of Transportation continually informed of any movements occurring in the affected area.