Landslide Deposit Erosion and Reworking Documented by Geomatic Surveys at Mount Meager, BC, Canada

Author:

Parizia Francesco12ORCID,Roberti Gioachino3ORCID,Clague John J.4,Alberto Walter5,Giardino Marco6ORCID,Ward Brent4,Perotti Luigi1ORCID

Affiliation:

1. Department of Agriculture, Forest and Food Sciences of Torino University, Largo Braccini 2, 10095 Grugliasco, Italy

2. Department of Civil, Construction and Environmental Engineering (DICEA), Sapienza University of Rome, 00184 Rome, Italy

3. Mount Meager Consulting, 17-38173 Westway Avenue, Squamish, BC V8B 0Y4, Canada

4. Department of Earth Science, Simon Fraser University, Burnaby, BC V6B 1R8, Canada

5. Arpa Piemonte, Via Pio VII, 9, 10135 Turin, Italy

6. Department of Earth Science, Torino University, Via Valperga Caluso 35, 10125 Turin, Italy

Abstract

Mount Meager is a deeply eroded quaternary volcanic complex located in southwestern British Columbia (BC) and is known for its frequent large landslides. In 2010, the south face of Mount Meager collapsed, generating a long-runout debris avalanche that was one of the largest landslides (50 × 106 m3) in Canadian history. Over the past 14 years, the landslide deposit has been reworked by stream action, delivering large amounts of sediment to Lillooet River, just downstream. In this study, we investigate 10 years of geomorphic evolution of the landslide deposit using orthophotos and digital elevation models (DEMs) generated using Structure from Motion (SfM) photogrammetry on aerial photographs acquired during unmanned aerial vehicle (UAV) and Global Navigation Satellite System (GNSS) surveys. The SfM products were used to produce a series of precise maps that highlight the geomorphological changes along the lower Meager Creek within the runout area of the landslide. Comparison of DEMs produced from 2010, 2012, 2015, and 2019 imagery allowed us to calculate deposit volume changes related to erosion, transport, and redeposition of landslide material. We estimate that about 1.1 × 106 m3 of sediment was eroded from the landslide deposit over the period 2015–2019. About 5.2 × 105 m3 of that sediment was redeposited inside the study area. About 5.8 × 105 m3 of sediment, mainly sand, silt, and clay, were exported from the study area and are being carried by Lillooet River towards Pemberton, 40 km from Mount Meager, and farther downstream. These remobilized sediments likely reduce the Lillooet River channel capacity and thus increase flood hazards to the communities of Pemberton and Mount Currie. Our study indicates a landslide persistence in the landscape, with an estimated 47-year half-life decay, suggesting that higher flood hazard conditions related to increased sediment supply may last longer than previously estimated. This study shows the value of using SfM in tandem with historic aerial photographs, UAV photos, and high-resolution satellite imagery for determining sediment budgets in fluvial systems.

Funder

SOCIETAL CHALLENGES—Climate Action, Environment, Resource Efficiency and Raw Materials

Publisher

MDPI AG

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