Geology Reference
In-Depth Information
important natural hazards in terms of loss of life, however, are land-
slides, earthquakes and volcanoes.
There are more than 300 fatal landslides each year on average (Petley,
2011). Some of these are in man-made slopes and therefore a matter
for engineering design (
Chapter 6).
Many, however, are in natural
slopes and single incidents can cause many deaths. The debris
ow
that struck Gansu, China, in August 2010, killed more than 1,200
people and destroyed at least 300 buildings. A total of 45,000 people
had to be evacuated. The risk to sites from natural terrain landslides is
therefore an important consideration at many sites.
Natural terrain landslides can be split into those where the detached
debris directly impacts a site through gravity and those where the
debris becomes channelised and
flows down a valley (
Figure 3.57).
Channelised landslides are relatively easy to deal with conceptually, in
that the pathway for the debris, which often becomes saturated and
flows, is easily predicted, even if the size of the event is not. The best
thing to do is to avoid the outlet of any valley, but if this is not possible,
Open hillside failure (OHF) within 100 m
of river
debris reacjes valley
debris reacjes valley
temporary dam forms then is
breached
temporary dam forms then is
breached
D
D
A
A
Shallow crest failure
in cut slope
crest failure
ut slope
B
B
OHF within 100 m of
facility at risk
F within 100 m of
facility at risk
D+
D+
C
C
Channelised debris
flow
Rock fall debris from cut
slope or threatening cliff
hazardous where they directly threaten a facility. Remote landslides can,
however, feed into a stream channel where they can be channelised and
ow
great distances. Things may be made worse where the initial failure produces a
landslide dam, behind which a lake forms. When the temporary dam is
breached, a sudden discharge of
fluidised debris is released.
