The 2010 Mount Meager landslide was a large catastrophic debris avalanche that occurred in southwestern British Columbia, Canada, on August 6 at 3:27 a.m. PDT (UTC-7).

[9][10] The massif has been a source of large volcanic debris flows for the last 8,000 years, many of which have reached several tens of kilometres downstream in the Lillooet River valley.

The rockfalls fell approximately 500 m (1,600 ft) onto Meager's weak and heavily saturated south flank where they destabilized a significant volume of material, forming a highly mobile, very rapid debris flow.

The landslide dam ultimately failed into the Lillooet River valley, releasing roughly 2,650,000 m3 (94,000,000 cu ft) of water towards Pemberton with an average velocity of approximately 2.5 m/s (8.2 ft/s).

[1][11] The landslide consisted mainly of intrusive porphyritic rhyodacite, lava flows and breccia derived from the Capricorn and Plinth assemblages, which are the most recently formed geological formations comprising the Mount Meager massif.

Sediment moving downstream puts pressure on the Pemberton district diking system, raising the effective flood levels.

[1] The landslide generated long-period seismic waves that were visible at seismograph stations from southern California to northern Alaska, up to 2,800 km (1,700 mi) away.

[1] Landslides do not always generate identifiable seismic signatures due in part to their slower source process and poor ground coupling as compared to earthquakes.

K. Kraliz, J. Duffy, J. Tilley and P. Smith arrived at upper Lillooet forest campsite at 3:25 a.m. PDT and began unloading their gear.

Chaos ensued for the next few hours before daylight as they encountered debris flows, mud, falling trees and other hazards at the edge of the landslide deposit in the Lillooet River valley.

[1] As of this edit, this article uses content from "The 6 August 2010 Mount Meager rock slide-debris flow, Coast Mountains, British Columbia: characteristics, dynamics, and implications for hazard and risk assessment", authored by Guthrie et al., which is licensed in a way that permits reuse under the Creative Commons Attribution-ShareAlike 3.0 Unported License, but not under the GFDL.