日本雪氷学会北信越支部学習会(8月22日)のおしらせ

8月22日に北信越支部学習会を下記の通り雪氷防災研究センターにおいて開催い
たします。
今回は来日されている Dieter Issler氏(NGI、ノルウェー地球工学研究所）に
話題を提供していただきます。所属されているノルウェー地球工学研究所の
雪崩のデータベースの中で、14°という最小の見通し角を記録した雪崩について
の話題です。

暑い折ではございますが、皆様ぜひお越し下さい。

記

日　時：2014年8月22日(金) 15:00～

場　所：新潟県長岡市栖吉町前山１８７－１６
雪氷防災研究センター　大会議室（2F）

話題提供者/題目

Dieter Issler（NGI、ノルウェー地球工学研究所）

*How can snow avalanches attain a run-out angle of 14 degrees?*

要旨

Once in a while, snow avalanches with unexpectedly long run-out are
observed. A striking and well-investigated event is the 1994
dry-snow avalanche at Bleie, south-western Norway that went more
than 1 km farther than usual and destroyed a farm that had been
unharmed for 700 years at least. Surveys on Svalbard (approx. 80
deg. N) revealed several small to medium-size avalanches that
reached much farther than one reasonably would expect. Near Davos,
Switzerland, a small wet-snow avalanche with a run-out angle of
only 16 deg. occurred in 2004. The present "record holder" in NGI's
database, however, is a medium-size dry-snow avalanche in
mid-eastern Norway that had a run-out angle of only 14 deg. This is
over 6 standard deviations less than the prediction of the
topographical-statistical alpha-beta model developed for Norway.

Even though such events have low annual occurrence probability,
perhaps of the order of 0.001, they cannot be neglected in hazard
mapping and land-use planning: Present regulations in Norway forbid
building single-family homes in areas where the annual avalanche
probability is larger than 0.001. For multi-family homes or public
buildings, the maximum allowed annual probability is 0.0002. On the
other hand, if one assumed an extreme run-out angle of 14 degrees
everywhere, most of Norway would be uninhabitable. It is therefore
of great importance to understand the circumstances that lead to
extremely long run-out, and to characterize the associated flow
regime.

In this talk, avalanche flow regimes and the conditions of their
occurrence will be discussed. In particular the
intermediate-density fluidized flow regime may be relevant for the
long-runout problem. Fluidized flow has often been observed in
dry-snow avalanches and was studied in the laboratory by Nishimura
and Maeno, but remains incompletely understood. The presentation
concludes with preliminary thoughts on how these mechanisms might
be included in numerical flow models.