Mountain tsunamis – a rising threat

Mountain tsunamis – a rising threat
Navin Singh Khadka
chinadialogue, May 24, 2011
www.chinadialogue.net/article/show/single/en/4310-Mountain-tsunamis-a-rising-threat

Earthquakes could burst glacial lakes in the Himalayas, flooding
populated areas downstream, scientists are warning. Navin Singh Khadka
reports.

Glacial lakes in the Himalayas could pose a major hazard to population
centres if they are ruptured by earthquakes, scientists say. The true
risk to settlements and infrastructure downstream in the Hindu
Kush-Himalayan region is difficult to assess. But the Himalayan region
is dotted with glacial lakes and is in a seismically active zone.
Experts say that, on the basis of past records, a large quake in the
region is overdue.

Many glacial lakes are said to be growing – some of them alarmingly fast
– because of melting glaciers. Some are at risk of rupturing, which
would flood areas downstream. There have been at least 35 glacial lake
outburst events in Nepal, Pakistan, Bhutan and China during the last
century, according to the United Nations Environment Programme (UNEP).
But the increased risk from the quake-induced rupture of glacial lakes
has been rarely discussed.

"Such a disaster is very much possible, more so, when we are expecting a
big earthquake in the region now," says Sushil Kumar, a geophysicist
with the Wadia Institute of Himalayan Geology in India. "If the
acceleration is very high in the epicentre of the earthquake, everything
will be in the air as things will not be stable. So, naturally, the
liquids like waters in glacial lakes will burst out."

A number of these lakes are located near seismic faults. "Given the
location of the lakes, if the epicentre of the earthquake happens to be
nearby them, they will certainly explode," says Pradeep Mool, a
glaciologist with the International Centre for Integrated Mountain
Development (ICIMOD), which works on mountain issues in the region.

A recent report produced by ICIMOD, together with the World Bank and the
Global Facility for Disaster Reduction and Recovery, has also said that
such a hazard "is a possibility that should be considered, although
prediction [of earthquakes] is beyond current competence."

Officials with Nepal's National Seismological Centre (NSC) say at least
half a dozen minor tremors are recorded in the Himalayas every day. "And
when the tremor is [magnitude] five or above... we record many
aftershocks as well," says Dilliram Tiwari of the NSC. "We know that
these activities are happening in the Himalayas but we cannot confirm if
they are happening nearby any glacial lakes." That is because hardly any
seismic meters are installed near glacial lakes.

The danger is not just from the lakes that are filling up. Landslides
and avalanches can make even smaller lakes dangerous, especially during
earthquakes, experts say. For instance, the outburst of the Dig Tsho
glacial lake near Mount Everest in eastern Nepal in 1985 was triggered
by a large ice and rock avalanche. The splash into the relatively small
lake led to an outburst. The floodwaters swamped a hydroelectric plant
and other infrastructure downstream.

Tsho Rolpa is one of Nepal's most monitored glacial lakes. The lake is
risky not just because of its growing size and weak moraine, but also
because it has two hanging glaciers high above it. "In case of
earthquakes, glaciers such as these can make the glacial lakes like Tsho
Rolpa even more dangerous because of the possibility of splash and
surge," says Mool.

Although not created by glacial melting, a lake that formed after a
landslide blocked the Hunza river in Pakistan last year was caused by an
earthquake, says professor Asif Khan, a geologist with Peshawar
University in Pakistan. What has happened in these lower parts of the
Hindu Kush-Himalaya could also occur in higher areas with glacial lakes,
he warns.

"The main reason why we have not yet witnessed the outburst of glacial
lakes because of earthquakes is because the region has not been hit by
big ones in recent decades," says Sushil Kumar of the Wadia Institute of
Himalayan Geology. "And when the last earthquakes hit the region, there
were barely any glacial lakes in the Himalaya region." Glaciologists say
the round of glacial melting leading to the formation of most new
glacial lakes in the Himalayas began in the 1950s. The last big
earthquake to hit the region was in 1934.

A recent report on Nepal's glacial lakes said their average area had
increased by 33%. "A great number of people are potentially in danger
should the lakes classified as dangerous in the Hindu Kush Himalayas
drain," says another report by UNEP. "In most cases, there would be
little or no warning, with insufficient time for complete evacuation."

But studies have so far focused only on retreating glaciers and
expanding glacial lakes. "They have not been monitored in relation to
seismicity," says Khan. "It is indeed quite worrying given the scale of
the impending risk."

Navin Singh Khadka is a journalist with the BBC Nepali service. He has a
sustained interest in environment, with a focus on climate change
vis-a-vis Himalayan ecology.

An earlier version of this article appeared on the BBC Science and
Environment website. It is reproduced here with permission.
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