The Zymoetz River rock avalanche, June 2002, British Columbia, Canada

Abstract

On June 8, 2002, the Pacific Northern Gas pipeline in the Zymoetz River valley was severed by a large debris flow. The event initiated as a rock avalanche in Glen Falls Creek, a tributary of the Zymoetz River. The rock avalanche involved 1 × 10 6 m 3 of volcaniclastic bedrock, and travelled through a complex flow path, to finally deposit a large fan in the main Zymoetz River. Approximately half of the debris volume was deposited in the cirque basin at the head of the valley, with the rest deposited in the channel, and the fan. Examination of the initiation zone showed a very persistent, slightly curved, joint set that forms the main sliding surface for the failed block with a dip of 45°, and dip direction of 300°. A Geographic Information System (GIS) was used to examine the event and allowed for further interpretation of field data. Preliminary dynamic analysis indicates that the event reached velocities of up to 34 m/s. Comparison of the Zymoetz River rock avalanche (ZRRA) with other similar events from the literature indicates that it exhibited similar mobility and velocities. As evidenced from the literature, these long runout events can cause significant damage, and have the potential to be a very high risk as forestry and recreation activities spread further into remote areas.