Yosemite Rockfall Video

Sam Crawford a former associate in county government suggested I might like this video. I did enjoy it. It is interesting to me at multiple levels as I have had to assess rock fall hazards on numerous occasions as a consulting engineering geologist.
Washington State does not have cliffs as dramatic as the shear granite walls of Yosemite, but we do have plenty of overesteep glacial valleys in the Cascade and Olympic Mountains as well as the Columbia Highlands, the Columbia River Gorge, the scab land cliffs in eastern Washington and the San Juan Islands.
Washington State's Growth Management Act requires counties and cities to have Critical Areas Ordinances. Critical Areas Ordinances are used to protect wetland areas, wildlife habitat and to protect the public and property owners from geologic hazards. Rockfall hazards fall under geologic hazards. If there are steep potentially unstable slopes an assessment of the geology hazard will likely be required before a building permit is issued. I have assessed the potential for rockfalls impacting a proposed building site when the site is located below a cliff area or the impacts of development on the stability of a slope that may generate rockfalls. The most recent project I assessed where rockfall was a concern was up the Skagit River Valley in the North Cascade Range. My conclusion was that the hazard was essentially nil for the proposed building site. At another site I ruled out building on one portion of the property that had been previously prepared for development. My conclusion was the risk was very low, but the consequences was very high. That site was more like the sites in Yosemite although at a much smaller scale. I have had only one property where I completely ruled out development due to rock fall hazard. That site was on a small lot on Orcas Island. Last fall I assessed a site on Fidlago island specifically for rock fall hazards. Sure enough there were large boulders in the woods on flat ground not unlike the boulders in the video of Yosemite. However, all of the boulders were covered in moss and lichen and hand digging underneath the boulders as well as elsewhere on the site I found the soils were indicative of ice wasting. The boulders on the flat area were most likely boulders left behind by melting glacial ice. Scrambling on the bedrock slopes and overgrown and mossy talus on the slopes above I found no evidence of recent rock fall and could not find any potential rock fall sites at least above the property I was interested in. However, further to the west of the site I found lots of hazardous cliffs and relatively recent rock falls so the County geologist was warranted to be concerned.