Observations on the May 2019 Joffre Peak landslides, British Columbia

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Two catastrophic landslides occurred in quick succession on 13 and 16 May 2019, from the north face of Joffre Peak, Cerise Creek, southern Coast Mountains, British Columbia. With headscarps at 2560 m and 2690 m elevation, both began as rock avalanches, rapidly transforming into debris flows along middle Cerise Creek, and finally into debris floods affecting the fan. Beyond the fan margin, a flood surge on Cayoosh Creek reached bankfull and attenuated rapidly downstream; only fine sediment reached Duffey Lake. The toe of the main debris flow deposit reached 4 km from the headscarp, with a travel angle of 0.28; while the debris flood phase reached the fan margin 5.9 km downstream, with a travel angle of 0.22. Photogrammetry indicates the source volume of each event is 2-3 Mm3, with combined volume of 5 Mm3. Lidar differencing, used to assess deposit volume, yielded a similar total result; although error in the depth estimate introduced large error and masks expected increase due to dilation and entrainment. The average velocity of the rock avalanche-debris flow phases, from seismic analysis, was ~25-30 m/s, and the velocity of the 16 May debris flood on the upper fan, from super-elevation and boulder sizes, was 5-10 m/s. The volume of debris deposited on the fan was ~104 m3, 2-orders of magnitude less than the avalanche/debris flow phases. The 13 May landslide was apparently triggered by rapid snowmelt; with debuttressing triggering the 16 May event. While spring 2019 was warm, it wasn’t unusual. It is likely that progressive glacier retreat and permafrost degradation were the conditioning factors; precursor activity was noted at least 1 yr previous; thus, the mountain was primed to fail and average seasonal snowmelt tipped the balance.

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Publication type Article
Publication Subtype Journal Article
Title Observations on the May 2019 Joffre Peak landslides, British Columbia
Series title Landslides
DOI 10.1007/s10346-019-01332-2
Volume 17
Year Published 2020
Language English
Publisher Springer
Contributing office(s) Geologic Hazards Science Center
Description 18 p.
First page 913
Last page 930
Country Canada
State British Columbia
Other Geospatial Joffre Peak
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