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,**/  .  ,1  ,**0  +  1 Time Variation of Volcanic Plume Related with the Eruptions of Asama Volcano in ,**.
Tsuneomi KAGIYAMA῍ and Etsuro KOYAMA῍῍Asama Volcano had a series of eruptions from September + to November +., ,**.. We have carried out
infrared observation at the eastern foot of the volcano since August ,**,, and have succeeded in capturing
successive plume imageries. We examined long term and short term variation in volcanic plumes related with the,**. Eruptions.
We examined long term variation of the plume height from January to November ,**., and found two
di#erent kinds of correlation between the plume height and other volcanic activities ; the increase in plume height
followed by the eruption with a long time delay, and that followed by the eruption promptly. The plume heightturned to increase gradually in March and May with the increase of the A-type earthquakes and gradual inﬂationsuggesting supply of magma in the deeper part, and the height increased anomalously from July ,/ with rapid
inﬂation suggesting magma migration to the shallower part. These anomalies were followed by the ﬁrst eruption
on September + about .* days after. Erupted products included some juvenile materials, but the major part of theproducts were lithic materials. The plume height became lower just after the eruption, but turned to increase
from September +, following the increase of A-type earthquakes. The second eruptive stage started from
September +., , days after the increase of the plume height. Three small eruptions occurred on September +.,and many small eruptions occurred successively from September +0 to +1. The erupted products were mostly well
vesiculated juvenile materials. This evidence suggests that the eruptions in the second stage occurred with much
volcanic gas, while the ﬁrst eruption occurred after degassing from magma.
We examined short term variation of the volcanic plume during the developing stage of the successive minor
eruptions ; from ** : /1 a.m. to *2 : ** a.m. on September +0. We got time series data of the average temperatureon the certain vertical line segment, which is crossed by moving volcanic plume, and examined spectrums. As aresult of analysis, some power peaks were conﬁrmed at the multiples of *.**,/ Hz until . a.m. And this peak wasfound to move to higher frequency according to the eruptive activity ; *.**-, Hz at 1 a.m. One possible reason isthat Asama Volcano has some resonance beneath the crater (conduit), and the characteristic length of the conduit
changed to be shorter during the successive minor eruptions. Japan Meteorological Agency reported the numberof eruptions increased from . a.m., and Geographical Survey Institute found a lava cake within the crater about++ a.m. These evidences suggest that magma ascended within the conduit around . or 1 a.m., and may beconsistent with our analytical results.
Key words : Asama Volcano, eruption, volcanic plume+ῌ ῐ ῎ ῑ ῏) &*+,*-. /01& 23  !"!" #$%$%&'(456789*:+;$%$%&<'(!=*>203ῌ+.*. ?@ABCDEBCFGH /,2*IJKLKLMLNOPQRSLNOTUNOVWXY
Aso Volcanological Laboratory, Graduate School ofScience, Kyoto University, Minami-Aso, Aso, Kumamoto 203ῌ+.*., Japan.
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Asama Volcano Observatory, Earthquake ResearchInstitute, University of Tokyo, Nagakura-Yama, Karuizawa, Nagano -23ῌ*+++, Japan.
Corresponding author : Tsuneomi Kagiyama
e-mail : kagiyama@aso.vgs.kyoto-u.ac.jp