Water Stewardship Information Sources
| Citation | Guthrie, RH, Brown, KJ. 2008. Denudation and landslides in coastal mountain watersheds: 10,000 years of erosion. Geographica Helvetica 63: 26-35. |
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| Organization | BC MoE |
| URL | http://cses.washington.edu/cig/outreach/seminarfiles/2010seminars/Guthrie_Brown2008.pdf |
| Abstract/Description or Keywords | Landslides are primary denuders of the landscape since they directly transport sediment from upslope sources to both stream networks and lower more stable positions. Precipitation and earthquake triggered landslides in coastal British Columbia, Canada, annually erode the surrounding landscape concurrent with other dynamic modes of erosion such as stream incision and runoff. Here, we present a conceptual model of landslide-induced denudation for coastal mountain watersheds spanning 10,000 years of environmental change. Given that climate has varied substantially during the Holocene from warm-dry to cool-wet, the model fosters important insight into the interaction between climate and landslide-induced denudation. Further, the model considers recent and deleterious anthropogenic activity, mainly logging, and provides a framework by which human-induced denudation rates can be contrasted to those of the Holocene. Setting. Vancouver Island is located off the southwest coast of British Columbia, Canada (Figure 1). The island is comprised of 31,788 km2 of highly variable terrain, with the interior of the island containing the steep and rugged volcanic and intrusive Vancouver Island Ranges (Guthrie 2005a; Massey et al. 2003a, 2003b; Yorath & Nasmith 1995). The largest mountain peaks attain elevations of c. 2,200 m. Average annual precipitation varies longitudinally across the island, with eastern rain shadow areas receiving as little as 700 mm of annual rainfall compared to >3,500 mm of rainfall on the oceanic west coast (Environment Canada 1993, 2007). The moist and mild climate supports widespread temperate rainforest in the lowlands. At high elevations, cooler temperatures coincide with alpine forest and tundra. The island is located near the surface trace of the Cascadia subduction zone and is tectonically active (Adams 1984; Clague & James 2002; Dragert 1987). At least two earthquakes of sufficient magnitude to cause landslides occurred in the last century (Cassidy et al. 1988; Keefer 1984; Mathews 1979; Rogers 1980). Further, on a longer (semi-millennial) timescale, Vancouver Island is subject to large earthquakes of >8 magnitude (Atwater 1987; Leonard et al. 2004; Satake 1995). In addition to tectonic activity, Vancouver Island has been significantly modified by Pleistocene glaciation (Clague & James 2002; Ryder & Clague 1989), resulting in steep U-shaped valleys in the mountainous regions. On the mid and lower slopes, till and glaciofluvial deposits blanket the landscape. Subsequent post-glacial erosion and denudation has fostered the development of widespread shallow colluvium. |
| Information Type | article |
| Regional Watershed | Vancouver Island South, Vancouver Island North |
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| Contact Name | Richard Guthrie |
| Contact Email | [email protected] |