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What
are my risks?
What
areas are prone to landslides?
Areas
generally more prone to landslides are those located at:
- previous
landslides
- base of
slopes
- base of
minor drainage hollows
- base or
top of an old, filled slope
- base or
top of a steep, cut slope
- developed
hillsides with leach-field septic systems.
SOURCE:
State of California Department of Conservation, Sacramento,
CA and National Landslide Information Center, U.S. Geological
Survey, Denver, CO
Recent
Kauai Landslides
Soil avalanches:
In Hawaii, valley walls are typically covered by soil
which is held to the bedrock by plant roots. We can find
soil avalanches or landslides taking place on the western
side or even northern side of Kauai.
Soil avalanches
may leave bright scars on the hillside for months. A good
example is a slide which occurred in Olokele Canyon
on Kauai in October, 1981. The slide face was about
300 meters wide and about 800 meters high. That's a thousand
feet wide by 2,400 feet high, a slide of tremendous proportions.
This particular
slide was caused by a combination of high rainfall and
underground water seepage. Features like this or processes
like this are responsible for much of the valley development
here in Hawaii.
Slow earth
movement: One other thing to note is that soil creep
is not a dramatic process but especially important. It's
a slow, imperceptible, continuous process where the movement
may be only a centimeter or so per year, but it is a very
important process, and it's especially important in housing
and commercial developments.
Hillside
cut: Here where houses are built on the side of the
hill, even very slow movements may cause the house to
break. It may cause telephone poles to bend very slowly.
It may cause fences to move.
Road cuts:
How many times have we seen landslides along road
cuts? The Department of Transportation mitigates landslides
near roadways by erecting chicken wire strapped around
the edge of the cliff. The purpose of this is to prevent
rockfalls and other things from sliding out onto the highway.
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