> Watersheds > Vegetation and Topsoil > Erosion > Hot Topic: Landslides
Do clearcuts and forest roads cause
a large storm in November, 1996, four people were killed
near Roseburg when a landslide destroyed their home. The
landslide originated in a clearcut, and many people have
blamed logging for these deaths. Does clearcut logging cause
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occur naturally. Landslides even occur in pristine forests
where no trees have been cut and there are no roads. They
are usually caused by the buildup of groundwater during
intense rainstorms. High risk areas, or those areas where
landslides are most likely to occur, are steep slopes just
below ridgetops. High risk areas may have thin soil, and
hollows or depressions that collect water during storms.
Most research indicates that clearcut
logging can increase the risk of landslides, especially
in high risk areas during the first ten years or so after
logging. How much does the risk increase? That's hard to
say, because the results from different studies don't agree
,and there are many variables, such as geology, weather,
and logging practices. Some estimates of the effect of logging
may be exaggerated, because, when viewed from the air, it
is easier to see landslides in clearcuts than in older forests.
Some studies have actually shown a decrease in landslides
flow downhill into streambeds at the bottom
of canyons, so the debris from many
landslides will be deposited in the same place. This makes
it easier to predict areas that are in danger from landslides,
no matter what the cause.
about roads? Researchers have known for a long timethat
roads can cause landslides. Roadcuts are steeper than natural
hill slopes, and roads change the flow of surface water
road design and construction has improved in the last 20
years, and roads are more often built along ridges instead
of on steep slopes. The Oregon Forest Practice Rules strengthened
the requirements for forest roads in 1983. During the 1996
storms, roads built since 1983 appeared to cause fewer and
smaller landslides than older roads.
The Oregon Department of Forestry can
now restrict clearcut logging and road building on steep
slopes above highways and homes if it is determined that
it could present a hazard to public safety or property.
Research is underway to learn more about the effect of logging
on landslides. It is important to remember, however, that
even if no trees are cut in high-risk areas, there is still
a risk of landslides during intense rainstorms.
- Public safety requires curbs on clear-cutting,
construction. Statesman Journal, Salem, September 17,
- Pyles, M., P.W. Adams, R.L. Beschta,
and A.E. Skaugset. 1998. Forest practices and landslides:
a report prepared for Governor John A. Kitzhaber. Forest
Engineering Department, Oregon State University, Corvallis.