Natural Weathering Caused Squamish Chief Rockfall: Geotech Report

By Gagandeep Ghuman
Published: May 19, 2015

The Squamish Chief rock fall on April 19 is being attributed to natural physical weathering processes, according to a geological report commissioned by the district. The report by GeoPacific consultants noted events of similar magnitude have a return period in the range of 50 to 150 years along the North Walls area of The Chief.

The report said that it appears that the rock fall occurred as a result of root jacking behind the failed block which in turn crushed the supporting weathered and fractured pedestal of rock below that rock, the report said.

The rock that completely detached on the backside was likely on the brink of failure for some time as the roots jacked it outwards.

This coupled with the completely detached geometry of the area where rock and the overhanging nature of the front face would have caused the centre of gravity of the block to shift outward, inducing additional downward pressure on the supporting rock pedestal.

The supporting rock was highly jointed and slightly weathered and noted by climbers as being “loose”, according to the report.

The report recommend that the Mamquam FSR remains open to normal vehicle use but signage be installed for vehicles are passing through a rock fall hazard area and that no stopping or parking be allowed.

The report also recommends that the Angels Crest access trail should be closed until the hazard from the source area above the base of the Angels Crest climb and along the Alaska Highway climb is determined to be acceptable, or measures acceptable to stakeholders have been implemented.

 Meanwhile, Global Rock Works has been hired by BC Parks to do follow-up work on the rock fall on the Chief. The company will do rock scaling (removing loose surface material presenting a rockfall hazard, usually with pry-bars and picks and on rope systems) on 10am-3pm from May 20-21. The public is asked to observe all trail closurs and to stay away from the area until further notice.