Dams hold danger of floods when strong earthquakes hit
Himalayas
By Scientific American, adapted by Newsela staff
09.10.15
Earthquakes can create massive amounts of
damage. The people of Nepal, a nation of 27
million located in the Himalayan mountain range
south of China, know this all too well. Earlier this
year, two massive earthquakes struck in the
Himalayas, killing more than 8,500 people.
The people of Nepal are still recovering.
Scientists, meanwhile, are already worrying
about the next earthquakes that will strike the
region. One growing concern has to do with the
dams in the Himalayas. More than 600 large
dams have been built or are in some stage of
construction or planning in the mountains.
Scientists are worried that a large earthquake
could cause some of the dams in the Himalayas
to burst. A burst dam would release a sudden
flood of water, posing a grave threat to local
communities.
Nepal Quakes Caused Damage
The 2015 earthquakes that hit Nepal cracked or
damaged several dams. The next earthquake
could be even stronger. According to a number
of engineers and scientists, many of the dams in
the Himalayas are probably not strong enough to
withstand the worst earthquakes that could hit
the region.
Burst dams would unleash huge quantities of
water, which would rush down through the
mountains toward towns and cities. A collapse of
Tehri Dam in the central Himalayas, for instance,
would set loose a wall of water about 650 feet
high. The water would hit two towns. The
flooding would affect six additional cities with a
combined population of 2 million.
Earthquakes occur in the region because of the
movement of layers of rock miles below the
surface. According to the theory of plate
tectonics, different pieces of the earth's crust
("plates") are in slow, steady motion. One plate
below Nepal, the Indian plate, is pushing under
the Asian plate. It moves roughly 6 feet per
century, but it regularly gets stuck. This leads to
a build-up of pressure. When the pressure
reaches a certain level, the plates become
unstuck, causing an earthquake. The Himalayas
are located on a "fault line," an area where two
plates push against each other below the
surface. Because of its location in the Himalayas,
Nepal experiences earthquakes.
"Great" Earthquake Seen As Likely
Laurent Bollinger is a seismologist, a scientist
who studies earthquakes, at the French
Alternative Energies and Atomic Energy
Commission. He has studied the effects of the
earthquakes that hit Nepal earlier this year.
According to Bollinger's research, the
earthquakes destabilized the region, making a
"great" earthquake more likely to occur in the
future. A "great" earthquake is any earthquake
that scores an 8.0 or higher on the Richter scale.
The Richter scale rates the strength of
earthquakes from 0 to 10. The two earthquakes
that hit Nepal in April and May 2015 were
measured as 7.8 and 7.3, respectively.
Other studies indicate that these earthquakes
released only a fraction of the pressure that has
built up between the plates below the Himalayas.
This suggests that more earthquakes are likely in
the coming years. Vinod K. Gaur is a
seismologist at the CSIR Fourth Paradigm
Institute in India. He says that there could be a
8.0 earthquake in the Himalayas in the near
future. If there are no earthquakes for 200 years,
the pressure will keep increasing. When an
earthquake finally comes, it will be even more
powerful.
Given the likelihood of more earthquakes in
Nepal, the dams in the region have to be
specially reinforced. They must be able to
withstand the strong ground shaking of an
extreme earthquake, says Martin Wieland of the
International Commission on Large Dams.
India, China Secretive About Dam
Designs
Part of the trouble is that scientists are not
always allowed to study the dams freely to
determine whether or not they are strong
enough. Most of the dams in the region supply
power to India and China. Although every nation
has its own regulations, India and China are
secretive about their dam designs. Outsiders are
rarely allowed to examine Indian and Chinese
dams.
Scientists who have been able to study dams in
the region have sometimes found cause for
concern. Probe International is a Canadian
environmental research organization. It studied
China's Three Gorges Dam. It found that the
designers had not considered worst-case
scenarios when designing the dam's earthquake
resistance.
Scientists Seek Safer Construction
If the Indian and Chinese governments have not
put in place the proper reinforcements, hundreds
of dams could be in danger of bursting when the
next big earthquake hits the Himalayas. If that
happens during a rainy season, when the dams
are full, the burst dams could create massive
damage.
A handful of scientists have taken the lead in
arguing for safer dam construction. They have
only had limited success, though. For now, all
they can do is call attention to the problem.
Scientists hope that, with the help of public
pressure, dams in the Himalayas will be
reinforced to withstand great earthquakes.
Otherwise, the next great earthquake in the area
may result in a man-made tsunami.