risk from dams
Large dams in mountainous
regions could threaten people living near them by stressing
the Earth's crust to danger levels, a scientist says. The
researcher says there have been recorded cases in several
countries of dam construction causing earthquakes. Large-scale
mining, he believes, can sometimes produce the same result.
He says parts of Africa are
especially vulnerable because of the tectonic forces that are
shaping the continent.
scientist, Chris Hartnady, is a former associate professor in
the department of geological sciences at the University of
Cape Town, South Africa.
was attending a conference here, the Africa Mountains High
Summit, hosted by the United Nations Environment Programme (Unep).
Hartnady says in his presentation: "Large areas of the
African continent are in an unstable, tectonically active
state, and especially in the mountain regions substantial
danger is posed to growing populations.
"The economic cost of
seismic and volcanic disasters is likely to escalate
dramatically during this century.
If you dig a big enough reservoir, you're going to get
earthquakes " Bill McGuire
Benfield Greig Hazard Research Centre
Mountain areas appear very
attractive places in which to site reservoirs or
hydro-electric schemes. However, in east and southern Africa,
these high-lying areas are usually associated with
tectonically active belts near faults and rifts in the Earth's
McGuire, director of the Benfield Greig Hazard Research Centre
in London, UK, says rising seismic and volcanic damage is a
"There's no question that
if you dig a big enough reservoir, you're going to get
"The Three Gorges Dam in
China is going to be a big problem," he told BBC News
"There's also the worry
that if you build a dam in mountainous terrain that you will
get landslides as it fills."
huge landslide behind the Vaiont dam in northern Italy in 1963
took the lives of over 2,500 people when a wave of water and
debris spilled over the dam and swept away a small town, he
Hartnady says the African continental crust is stressed to the
"fracture criticality" limit.
dams if you must, but engineer them much more sensitively than we do now Chris
told BBC News Online: "Partly this is because of the
African superswell, a mass of warm volcanic rock which is
rising under much of south-eastern Africa, producing a
buoyancy effect which is helping to pull the crust apart.
partly it's the forces at play in the boundary zone between
the Nubian and Somalian tectonic plates. Mining triggers
earthquakes in South Africa's high veldt."
late October 1995, the reservoir behind the Katse dam in
Lesotho began to fill. Days later people started feeling earth
tremors, and one measuring 3.1 on the Richter scale was
recorded on 3 January 1996.
am positive that was cause and effect. In 1964, a dam was
built at Koyna in India's Western Ghats. There was a big
earthquake in the region in 1967 - cause and effect again.
"So build dams if you
must, but engineer them much more sensitively than we do
Hartnady believes geohazards, including earthquakes, volcanic
activity and shifting soils, are an underestimated problem.
He says: "I wonder whether
for Africa they may be a more real and present danger than
climate change. We badly need more research, on the sort of
scale of the effort going into climate change.
are a problem in developed countries too, in places like
California and Japan. The US Geological Survey has a wealth of
expertise. But some of their knowledge just isn't applicable
in places like Africa with much slower rates of motion.
"In the San Andreas Fault
in California, the rate is something like 30-50 mm a year,
compared with 5-10 mm in the Rift Valley in East Africa. But
while 5 mm a year may not be sexy, it could be serious."
with the centuries-old records and monitoring from developed
countries, Africa's detailed seismological monitoring goes
back only about 40 years, Professor Hartnady says.
But he is confident that
science means it will soon be possible to predict the risks
much more accurately.
need to leapfrog to a new kind of technology, and it does
exist," he says. "There's everything space geodesy
can offer, including the global positioning system, very long
baseline interferometry, and satellite laser-ranging. These
will measure current rates of plate motion.
"I can't tell people now
when the risks will become acute. There could be a catastrophe
tomorrow, or we could get through this century without one.
"Come back in five to 10
years, though, when we can start to distinguish the signal
from the noise, and I'll give you the numbers. The sooner we
begin sophisticated monitoring, the sooner we'll have the