EGU21-16599
https://doi.org/10.5194/egusphere-egu21-16599
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Terrestrial overview of a landslide-tsunami-flood cascade at Elliot Creek, British Columbia 

Marten Geertsema1, Brian Menounous2, Dan Shugar3, Tom Millard1, Brent Ward4, Göran Ekstrom5, John Clague4, Patrick Lynett6, Jonathan Carrivick7, Pierre Friele8, Andrew Schaeffer9, Davide Donati4, Doug Stead4, Jennifer Jackson10, Bretwood Higman11, Chunli Dai12, Camille Brillon9, Derek Heathfield10, Gemma Bullard13, Ian Giesbrecht10, Katie Hughes1, and Mylène Jacquemart14
Marten Geertsema et al.
  • 1British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development, Canada (marten.geertsema@gov.bc.ca)
  • 2University of Northern British Columbia, Canada
  • 3University of Calgary, Canada
  • 4Simon Fraser University, Canada
  • 5Lamont-Doherty Earth Observatory, USA
  • 6University of Southern California, USA
  • 7Leeds University, United Kingdom
  • 8Cordilleran Geoscience, Canada
  • 9Natural Resources Canada, Canada
  • 10Hakai Institute, Canada
  • 11Ground Truth Alaska, USA
  • 12Ohio State University, USA
  • 13BGC Engineering, Canada
  • 14ETH Zürich, Switzerland

On 28 November 2020, some 18 Mm3 of quartz diorite detached from a steep rock face at the head of Elliot Creek in the southern Coast Mountains of British Columbia. The rock mass fragmented as it descended 1000 m and flowed across a debris-covered glacier. The rock avalanche was recorded on local and distant seismometers, with long-period amplitudes equivalent to a M 4.9 earthquake. Local seismic stations detected several earthquakes of magnitude <2.4 over the minutes and hours preceding the slide, though no causative relationship is yet suggested. Pre-slide optical and radar remote sensing data indicated some slope deformation leading up to failure. More than half of the rock debris entered a 0.6 km lake, where it generated a 115 m displacement wave that overtopped the moraine at the far end of the lake. We estimate that some 13.5 Mm3 of water left the lake from the combined impact of the landslide as well as erosion of the dam. The water that left the lake was channelized along Elliot Creek, scouring the valley more than 40 m in some places over a distance of 10 km before depositing debris on a 2 km2 fan in the Southgate River valley. Debris temporarily dammed the river, and turbid water continued down the Southgate River to Bute Inlet, where it produced a 70 km turbidity current and altered turbidity and water chemistry in the inlet for weeks. The landslide followed a century of rapid glacier retreat and thinning that exposed a growing lake basin. The outburst flood extended the damage of the landslide far beyond the limit of the landslide, destroying forest and impacting salmon spawning and rearing habitat. We expect more cascading impacts from landslides in the glacierized mountains of British Columbia as glaciers continue to retreat, exposing water bodies below steep slopes while simultaneously removing buttressing support.

How to cite: Geertsema, M., Menounous, B., Shugar, D., Millard, T., Ward, B., Ekstrom, G., Clague, J., Lynett, P., Carrivick, J., Friele, P., Schaeffer, A., Donati, D., Stead, D., Jackson, J., Higman, B., Dai, C., Brillon, C., Heathfield, D., Bullard, G., Giesbrecht, I., Hughes, K., and Jacquemart, M.: Terrestrial overview of a landslide-tsunami-flood cascade at Elliot Creek, British Columbia , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16599, https://doi.org/10.5194/egusphere-egu21-16599, 2021.

Corresponding presentation materials formerly uploaded have been withdrawn.