MUDSLIDES AND DEBRIS SLIDES are a common occurrence in the rainy season of southern California. The following images depict this problem and how people have managed to cope with the unstable slopes.
Background Information:
The processes of mass wasting are those that move weathered material down slope under the influence of gravity. Two factors play the major role in these processes - gravity and water. Gravity is the obvious driving force that constantly pulls material downward. Water has a dual role in mass wasting. The presence of water in debris makes it heavier and thus more prone to the gravitational force, and, it also has a lubricating aspect. A thin film of water or a confined area of water under pressure can allow materials that were stable in the dry state to move when wet.
A dynamic landscape along the coast of southern California. Dynamic in the
sense that it has moved and will in the future. The hills consist of
unconsolidated to poorly consolidated sediments that when wet, become unstable.
This slope consists of considerably higher amounts of consolidated rock but with
highly weathered zones and interlaced with unconsolidated material. As a
result precautions must be taken to protect the cars from rocks falling from the
cliff face. In this image a retaining wall is seen on the left at the
cliff base. To the right of it is a lower retaining wall build out of
concrete highway dividers. The effect is to hold back rocks that fall from
the cliff - especially during wet weather.
A closer look shows that in addition to the retaining walls a heavy screen has
been draped over the slope. This screen prevents the larger rocks from
falling away from the cliff face. (Check the larger images of these
pictures by following the links in the left margin.)
Another view of the screen.
A little further inland, but still on unstable slopes, a homeowner attempts to
prevent the land from sliding away by coating a portion of the hill with
plastic. The idea is a valid one - the plastic prevents the water from
soaking into the sediments. Unfortunately the size of the slope is so
large that a lot more plastic would be needed to be effective.
This is a closer view of the above picture. The house at the hill top.
Another attempt to stabilize the slope is construct physical barriers.
This concrete retaining wall under construction show the reinforcements on the
left side. To make the wall more aesthetic it has been covered with
sculpted rock.
This homeowner opted for black plastic. White sand bags hang down from
above in a somewhat successful attempt to keep the plastic in place.
Another way to stabilize the slope is to cover it with stone. But it is
obvious that this barrier must be maintained to remain effective.