IMPACTS AND DYNAMICS OF THE 2007 CHEHALIS LAKE LANDSLIDE-INDUCED WAVE USING LIDAR AND OTHER MAPPING TOOLS

Landslide-generated waves in lakes, fjords and rivers pose a threat to human settlements, natural resources and hydroelectric infrastructure. Their impact, however, remains poorly understood due to the scarcity of reported events and scant documentation. LiDAR (Light Detection and Ranging) is a useful tool for mapping the effects of landslide-generated waves and providing better understanding of the phenomenon. LiDAR has been used along with other remote sensing systems (SONAR and aerial photography) and field mapping to investigate erosional and depositional effects of waves and a seiche in Chehalis Lake (Coast Mountains, British Columbia, Canada) generated by a ca. 2-3 Mm_³ rockslide on 4 December 2007. The waves and seiche impacted the entire 18 km perimeter of Chehalis Lake, as well as Chehalis River downstream from the lake. Effects include stripping of soil, unconsolidated sediments and forest up to 25 m above lake level; deposition of organic debris up to ca. 30 m above lake level; log jamming at the outlet of the lake and along the Chehalis River; erosion of the banks of Chehalis River; and destruction of three campsites, which fortunately were unoccupied at the time of the event. Data gathered during this study and their initial interpretation improve understanding of landslide-generated waves in several ways. First, the data and observations elucidated the types and preservation potential of geomorphic evidence, including both subaerial and subaqueous features, that can be used to identify past events elsewhere. Second, mapping of wave run-up indicators and impacts provided information about the dynamics of the displacement waves and subsequent seiches. Third, the study provided field data (wave run-up, direction and energy indicators) that can be used to test and validate predictive numerical models.