Artikkelen under som jeg fant etter å ha skrevet den forrige malen min
bekrefter bl.a. hva jeg der hevdet om Andesfjellene. Videre sender jeg
en et år gammel artikkel om bresmelting verden over.
Karsten Johansen
Flood disaster threatens Himalayas
13:00 16 April 02
NewScientist.com news service
More than 40 lakes in the Himalayas could burst their banks at any time
and flood communities up to 100 kilometres downstream, according to a
new UN study. Very few of the people at risk would get any advance
warning.
The analysis of more than 5000 Himalayan glaciers and lakes revealed 20
in Nepal and 24 in Bhutan that are at bursting point. Hundreds more
lakes elsewhere in the Himalayas remain unsurveyed.
The lakes are formed as mountain glaciers melt, a process much
accelerated by global warming. The water is kept in place by ice or
piles of sediment, known as moraines, that were deposited when the
glacier was at its longest. But as the lakes grow, the moraines are
starting to collapse and every monsoon season, the risk of a disaster
grows.
"Unless urgent action is taken, any one of these lakes could burst its
banks with potentially catastrophic results," says Surendra Shrestha of
the UN Environment Programme. He warns that just two of the identified
lakes have early warning systems that would alert those that live in the
path of the threatened flood.
Dozens drowned
"These glacial lake outbursts used to be events that happened once every
500 years, but they have become frequent since 1950," says Shrestha.
There have been 12 glacial lake bursts in Tibet since 1935, says Pardeep
Mool of the International Centre for Integrated Mountain Development
(ICIMOD) in Kathmandu, who carried out the new survey. There have been
three major bursts in Bhutan since 1950 and a similar number in Nepal,
he says.
When the Sangwang Cho glacial lake in Tibet burst in 1954, the flood
damaged a city 120 kilometres away. A 15-metre wall of water burst from
the Dig Tsho lake in Nepal in 1985, destroying 14 bridges and drowning
dozens of people.
Two years ago, engineers in Nepal lowered one lake, Tsho Rolpa, by three
metres to ward off imminent collapse. They installed sensors in the
river bed below the lake that will set off sirens in villages below,
giving about 15 minutes warning and potentially saving 6000 lives.
But this arrangement remains unique in Nepal because there is no money
to help other threatened communities, says Mool.
Worldwide threat
He warns that lake bursts do not just threaten the Himalayas, as there
are thousands of mountain valleys above 5000 metres around the world
containing fast-growing glacial lakes.
The risk of such bursts has been recognised in the Peruvian Andes since
1970, when a glacial lake burst after an earthquake and killed 60,000
people. Since then, the authorities have siphoned water from some 40
Andean lakes to make them safe.
But five years ago, the work stopped. "This is really dangerous," says
Cesar Portocarrero, the Peruvian glaciologist who carried out the
surveys. "New lakes are forming all the time. But we no longer have them
mapped, so the risk of another big disaster grows."
Fred Pearce
------------------------
Meltdown
New Scientist 13:30 31 May 01
Most of the world's glaciers are shrinking, a new satellite survey of
over 2000 glaciers has revealed.
Concerns have been raised about melting glaciers on Mount Kilimanjaro in
the Tanzanian Himalayas and in the Glacier National Park in Montana (New
Scientist, 13 May 2000, p 28). Now infrared and visible photographs
taken by a Japanese instrument on board NASA's Terra spacecraft show the
shrinkage is happening on a global scale.
ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)
takes about two days to map the surface of the Earth, with a resolution
of about 20 kilometres. The instrument also has an unprecedented ability
to zoom in on sites of particular interest to resolutions as high as 15
km.
Glacier in Patagonia. Photo: NASA/GSFC/MITI/ERSDAC/JAROS/ASTER science
team
Rick Wessels of the US Geographical Survey in Arizona compared thousands
of ASTER images to aerial photographs dating back 20 years. He found
almost every mountain glacier in Patagonia, the Himalayas, the Alps and
the Pyrenees had shrunk by at least several hundred metres. In some
cases, the glaciers had shrunk by several kilometres.
"Some glaciers are more like snowbanks," Wessels told the American
Geophysical Union Meeting in Boston on 30 May.
Dark lakes
Wessels also looked at images of mountain lakes at the base of melting
glaciers. Many had grown over the last 10 years, and showed up dark blue
instead of light blue, indicating higher levels of sediments. This
suggests there has been increased erosion of the mountain by the
glacier, indicating higher flow rates of the ice - and higher
temperatures.
The three telescopes that make up ASTER take pictures in the visible,
infrared and thermal infrared parts of the spectrum. Snow, ice and
debris-covered ice can be distinguished by looking for particular
signature emissions - for example, high reflectance but low thermal
emissions indicate ice.
"The images have better than half a degree accuracy in temperature,"
says Kurt Thome of the Optical Sciences Center at the University of
Arizona.
Web link:
ASTER images
Eugenie Samuel, Boston
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