Debris Flow on a Seasonally Frozen Rupture Surface at Moose Lake, British Columbia Marten Geertsema, Menno van Hees, Marta Chiarle and Jennifer Hayek Abstract In early month of November 2007, a 1.4 km debris flow initiated on a steep south-facing slope above Moose Lake in Mount Robson Provincial Park, British Columbia. Snow meltwater was likely concentrated along a shallow sea- sonally frozen rupture surface, generating high pore water pressure. The debris flow bifurcated into two concentrated gullies before distributing as a debris flood on a snow-covered fan. The debris flow crossed a twin pipeline corridor and came to rest in a ditch against a highway berm. There was no damage to infrastructure. In many ways, the landslide resembles skin flows described in permafrost zones. Keywords Debris flow Á Debris flood Á Seasonal ice Á Snow Á South-facing slope Á British Columbia 1 Introduction Shallow flows, common in permafrost areas around the world have been studied in detail. Water from snowmelt and rainfall concentrates along the upper boundary of permafrosts in the active layer, generating high porewater pressures and thaw consolidation (McRoberts and Morgenstern 1974, Leibman 1995, Lewkowicz and Harris 2005). Less well known are shallow landslides that occur in a similar fashion over seasonally frozen ground (Guo and Shan 2011; Shan et al. 2012). In this chapter we briefly describe an example of the latter case. M. Geertsema (&) Á M. van Hees Á J. Hayek Ministry of Forests, Lands and Natural Resource Operations, Prince George, BC, Canada e-mail: marten.geertsema@gov.bc.ca M. Chiarle Consiglio Nazionale delle Ricerche—Istituto di Ricerca per la Protezione Idrogeologica U.O.S, Torino, Italy W. Shan et al. (eds.), Landslides in Cold Regions in the Context of Climate Change, Environmental Science and Engineering, DOI: 10.1007/978-3-319-00867-7_19, Ó Springer International Publishing Switzerland 2014 263