Legacy Of Mount St. Helens’ Eruption
Puts Thousands More Lives At Risk Than Explosion Did, By Stephen Luntz/ Η
κληρονομιά της έκρηξης του όρους της Αγίας
Ελένης θέτει χιλιάδες περισσότερες ζωές σε κίνδυνο από την έκρηξη, από τον
Stephen Luntz
When Washington State's Mount St.
Helens erupted in 1980, the 57 resulting deaths were the most recorded for a
volcanic eruption in the United States. Yet a report has warned these could be
a tiny fraction of the true toll if nothing is done to tackle the legacy the
outburst left behind. The danger lies in catastrophic floods that could be
unleashed through a failure of a natural dam created during the eruption.
When St. Helens blew its top, it
triggered an avalanche that dammed the Toutle River. Water could no longer
drain from Spirit Lake, raising the water level. If this dam was to fail
suddenly, the flood that would sweep down the river system would threaten 50,000
people living downstream.
Authorities were aware of this
threat and quickly put measures in place to reduce the risks, including a
2.5-kilometer (1.5-mile) tunnel to allow some of Spirit Lake's water to escape.
However, as time has gone on, the danger has faded in people's minds. A report
to the US Forest Service by the National Academies of Science warns that
engineering works to protect areas below the dam are in urgent need of
updating.
Rumbles from St. Helens earlier this
year gained attention as an indication the mountain might be about to erupt
again. That seems to have been a false alarm, but even if it was real, the ash
and lava of a repetition of the 1980 explosion would be unlikely to produce
anything like the damage of failure by the Spirit Lake dam.
Such a failure is, unfortunately, a
real risk. The pressure of water can cause dams to collapse, and the location's
high sediment loads increase the chances of this, particularly given the
frequent floods from higher up the mountain. Moreover, given its proximity to
the Cascadia Seismic Zone, and the local shaking from even small eruptions, earthquakes
are to be anticipated.
The report recommends repairs to the
tunnel and to sediment retention structures above the dam. It also suggests
consideration be given to the creation of a spillway or a second drainage
tunnel.
As dangerous as the Spirit Lake Dam is, it has
nothing on another natural blockage half a world away. In 1911 an earthquake in
Central Asia triggered a landslide that blocked the Murghab River and formed
Sarz Lake. The lake is hundreds of meters deep, and if the dam were to fail as
a result of a new earthquake, the resulting wall of water would wipe out 28
villages in the valley below. In the worst case scenario, more than 5 million
people living further downstream would be in peril. Geologists disagree,
however, on the likelihood of such an event.
Spirit Lake looks very peaceful, but
that is a lot of water to suddenly come rushing down without warning.
jennagenio/Shutterstock
http://pirforosellin.blogspot.gr/ -
Επιτρέπεται η αναδημοσίευση του περιεχομένου της ιστοσελίδας εφόσον
αναφέρεται ευκρινώς η πηγή του και υπάρχει ενεργός σύνδεσμος(link ). Νόμος
2121/1993 και κανόνες Διεθνούς Δικαίου που ισχύουν στην Ελλάδα.3443.
ΕΠΙΣΗΜΑΝΣΗ
Ορισμένα αναρτώμενα από το διαδίκτυο κείμενα ή
εικόνες (με σχετική σημείωση της πηγής), θεωρούμε ότι είναι δημόσια. Αν
υπάρχουν δικαιώματα συγγραφέων, παρακαλούμε ενημερώστε μας για να τα
αφαιρέσουμε. Επίσης σημειώνεται ότι οι απόψεις του ιστολόγιου μπορεί να μην
συμπίπτουν με τα περιεχόμενα του άρθρου. Για τα άρθρα που δημοσιεύονται εδώ,
ουδεμία ευθύνη εκ του νόμου φέρουμε καθώς απηχούν αποκλειστικά τις απόψεις των
συντακτών τους και δεν δεσμεύουν καθ’ οιονδήποτε τρόπο το ιστολόγιο.
Δεν υπάρχουν σχόλια:
Δημοσίευση σχολίου