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 :º»¬ ¼ ½/,*+* B +* C ,/ DEF ,*++ B / C ,* DE>The +12- Tenmei Eruption of Asama Volcano :Ash-fall Distribution and Sequence of the Eruption Review from Old Documents
Masashi TSUKUI῍
The +12- activity of Asama volcano was reviewed from May to the end of the year based on +00 old
documents, including those recorded at a distance.
+. Prior to the +12- Asama eruption, the level of magma head ascended at Kama-yama crater-pit.
Moderately explosive eruptions commenced on May 3, and repeatedly blew o# the plugged magma.
,. Depending on the wind direction, ash fell N, NNE, and NE of the crater including Sado Island, Tohoku
and Kanto districts. From August - to /, climactic plinian eruption dispersed pyroclastic materials. Distributions of 2 tephra- fall units were presented.
-. The timing of rumbling and quakes at distant places farther than +**km from the crater well correspondwith explosive events witnessed by neighbors of the volcano.
.. Duration of a single eruptive event rarely exceed 0 hours. It was true even during the culminating
plinian stage from Aug. - to /, +12-. The eruption was so violent in this stage that huge blocks larger than +*m were thrown from Kama-yama crater.
/. Documents concerning with Kambara pyroclastic ﬂow and subsequent debris avalanche occurred on
August /, suggested that an explosion on the northern ﬂank triggered collapse of northern sector. The event
occurred at about *2 : ** to *2 : -* am, which is 3* to +,* minutes earlier than estimations appear in previous
work.
0. Small and less frequent eruptions continued until January +/, +12..
Key words : Asama volcano, Tenmei eruption, old document, ash -fall, eruption sequence+ῌ ῐ ῎ ῑ ῏GH+IJKL%MNOPQ-.

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/ 0,0-῍2/,, 12312456789: +῍-12;<;<=><?@A
Graduate School of Science, Chiba University, +῍--,
Yayoi-cho, Inage-ku, Chiba, Japan ,0-῍2/,,Q¨©ªTU$HKLr   ῏   ! " ῏   #   $ % & ' ( ) * (+33-) +,-.Corresponding author : Masashi Tsukui
e-mail : tsukui@faculty.chiba-u.jp12 3 66

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Table +. List of old documents on the +12- Tenmei Asama eruption. (a) O$cial (daily)
reports of regional government, o$ce, temples or shrines. (b) Personal records of regional
o$cials. (c) Records of local government o$cials or knowledgeable individuals. (d)Disaster and observation reports to regional and local government. (e) Others or not clear.
 + 
(a)    (b) 
/0+1234'35' , (d) 6

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67

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ΐῐ῎ ῏ ῑ
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69

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70

Table +.

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Correlation between old Japanese time and solar time on Aug. /, +12- at Maebashi city.

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¼A7
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72
Table -.

!

Sequence of the +12- Tenmei Asama eruption.
 -

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Fig. +.

73

Distribution of fall-out tephra deposits of the +12- Asama eruption.
) +*+,-./0123)

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Fig. +.

Continued.

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

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Aramaki, S. (+3/0) The +12- activity of Asama volcano.
Part I. Japanese Journal of Geology and Geography, ,1,+23ῌ,,3.
Aramaki, S. (+3/1) The +12- activity of Asama volcano.
Part II. Japanese Journal of Geology and Geography, ,2,++ῌ--.
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Minakami, T.(+3.,) On the distribution of volcanic ejecta(Part II) The distribution of Mt. Asama pumice in +12-.
Bull. Earthq. Res. Inst., Univ. Tokyo, ,*, 3-ῌ+*0.
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Voight, B. (+32+) Time scale for the ﬁrst moments of the
May +2 eruption. The +32* Eruptions of Mt. St. Helens,
Washington. Lipman, P. and Mullineaux, D., editors. U.
S. Geological Survey Professional Paper, +,/*, 03ῌ20.
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