|Citation||Guthrie, RH, Brown, KJ. 2008. Denudation and landslides in coastal mountain watersheds: 10,000 years of erosion. Geographica Helvetica 63: 26-35.|
|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.
|Regional Watershed||Vancouver Island South, Vancouver Island North|
|Sub-watershed if known|
|Contact Name||Richard Guthrie|
|Contact Email||[email protected]|