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| Titel |
Glacier Lake Outburst Floods in Norway 2001 - 2009 |
| VerfasserIn |
Miriam Jackson, Rune Engeset |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250040854
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| Zusammenfassung |
| Several GLOFs or jøkulhlaups occurred in Norway during the first decade of the
millennium, the most significant being several from Rundvassbreen, an outlet glacier of
Blåmannsisen and one from Flatbreen, an outlet glacier of Jostedalsbreen. A number
of minor flood events occurred also. Many of the glaciers in Norway, especially
the maritime glaciers with high winter balance, demonstrated frontal advance and
positive mass balance in the 1990s. However, since 2000 most glaciers have had a
negative mass balance, and undergone frontal retreat and a corresponding decrease in
area.
The outburst flood from Flatbreen in 2004 was from a moraine-dammed lake that usually
drains under the glacier itself. The immediate cause of the flood was a sudden period
of warm, wet weather and the sudden increase of additional water into the lake
caused the moraine to rupture. Over 50 000 m3 of water drained from the lake, and
the resulting debris flow from the lake to the valley 1000 m lower had a volume
of 240 000 m3. Fortunately there were no injuries from this flood, but extensive
material damage to farmland on the valley floor. Previous, but smaller events occurred
from this lake in 1924 and 1947. The moraine is still partially ruptured, thus the
potential for a new jøkulhlaup of the same magnitude as that in 2004 is greatly
reduced.
Several floods occurred from a glacier-dammed lake at the glacier Blåmannsisen in Nothern
Norway, the first occurring in 2001, and subsequently in 2005, 2007 and 2009. The
jøkulhlaups all occurred in late summer, but at different water levels of the lake. The first two
events occurred when the lake was full and 35 – 40 million m3 of water drained. However, the
second event occurred a year after the lake had filled again, with the excess water in
the meantime draining over a spillway and away from the glacier, as it had done
prior to 2001. The two subsequent events occurred before the lake was completely
full, and were half the size of the first two events at about 20 million m3 of water.
The thickness of ice at the barrier has decreased over the past few decades, which
instigated the first event. Comparing measurements in 1961 and 1998, the part of
the glacier adjacent to the lake was up to 55 m thinner. Laser scanning performed
in autumn 2002 showed a further 4-10 of thinning between 1998 and 2002. GPS
measurements on the glacier surface showed that there was thinning of an average
of 4.5 m from 2001 to 2004, and a further 5-10 m between 2004 and 2009. This
further thinning led to the lake emptying under the glacier at a lower lake level than
previously. There were no human or material damages from any of these events. In
contrast, the floodwaters flowed into Sisovatn, a hydropower reservoir and were
financially beneficial. No similar events have been recorded before the 2001 event.
The lake is now expected to continue to empty under the glacier at fairly regular
intervals. |
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