This earthcache will give you a first hand look at the damage that
a landslide can do to the environment. Imagine if this landslide
had taken place in a populated area. The 1970 Simon and Garfunkel
song titled "Bridge Over Troubled Waters" which was followed by the
1977 Paul Simon song, "Slip Sliding Away," describe this area.
While these songs had nothing to do with this landslide it make for
an interesting comparison.
Some slopes are susceptible to landslides, whereas others are
more stable. Many factors contribute to the instability of slopes,
but the main controlling factors are the nature of the underlying
bedrock and soil, the configuration of the slope, the geometry of
the slope, and ground-water conditions. Once a landslide is
triggered, material is transported by various mechanisms including
sliding, flowing, and falling. Landslides often occur along planes
of weakness that may parallel the hill slope. Soils such as silt
and clay are weaker than rock and commonly have complex or multiple
planes of weakness. Landslides occur in slopes oversteepened by the
process of stream erosion or by the activities of man in grading
slopes. In many instances oversteepened slopes stand in apparent
stability until abnormally high ground-water conditions occur, thus
reducing the shear resistance and triggering the landslide. Once a
slope in a sensitive soil has been oversteepened by erosion at the
toe or by excavation work and the ground-water table is high, the
stage is set for a landslide to occur.
Three distinct physical events occur during a landslide: the
initial slope failure, the subsequent transport, and the final
deposition of the slide materials. Landslides can be triggered by
gradual processes such as weathering or by external mechanisms or
even a combination of factors. This type of slide is called a
rotational slide. Where the surface of rupture is curved concavely
upward and the slide movement is roughly rotational about an axis
that is parallel to the ground surface and transverse across the
slide. It was caused by a combination of factor going back to the
last ice age where as it retreated it left a fine layer of clay
that covered the region. The fact that the water was high for
several years cause the gradual undercutting of the river bank
which when coupled with heavy spring rainfall and run off cause the
bank to fail. The area above the slide had been recently logged
which changed the general nature of the spring run off. The heavy
rainfall induced increased erosion and oversteepening of the slope.
Besides this, the increased rainfall raised the water table, which
increased the pore water pressure, which in turn reduced the shear
resistance in the glacial marine clay causing it to liquefy and
finally slide.
DO NOT ATTEMPT TO ACCESS THIS CACHE FROM THE TRANS CANADA
HIGHWAY. This earthcache can be located by using an access road off
the Canterbury Exit. Just drive to the end of the access road where
it turns into an ATV trail from here either follow the ATV trail or
your GPS to the location.
At the coordinates listed above you will be in the general area
of the crown or top of the slide looking toward the river. To log
this Earthcache: Send an email to me through my profile with the
following information: What is the height of the main scarp at the
slide's crown. Use the diagram below to identify the parts of the
slide. Please begin your email with the name of the earthcache and
make sure your log includes the number of people in your group. It
also would be nice if you would post a photo so others would know
what they have to look forward to at this earth cache.
If you would like to explore the slide access is easiest along the
upstream edge of the slide, do not attempt to access the slide from
the top. For further information you might what to read: "Landslide
Types and Process" USGS Fact Sheet 2004-3072 July 2004
http://pubs.usgs.gov/fs/2004/3072/fs-2004-3072.html
