京 都 大 学 防 災 研 究 所 年 報 第47号 C 平成16年3月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 47 C, 2004

Study on the Evaluation Method of Volcanic Activity and the Improvement of Volcanic
Information: Preliminary Report

Kazuhiro ISHIHARA, Masato IGUCHI, Daisuke MIKI, Keigo YAMAMOTO, Wataru
KANDA, Takeshi TAMEGURI, Daisuke FUKUSHIMA*, Takehiko MORI*,
Hiromitsu OSHIMA**, Jun-ichi HIRABAYASHI***, Kenji NOGAMI***and Yasuaki SUDO***** COE Researcher, DPRI, Kyoto University** Graduate School of Science, Hokkaido University, Japan***Volcanic Fluid Research Center, Tokyo Institute of Technology, Japan**** Graduate School of Science, Kyoto University, Japan

Synopsis
This paper is a preliminary report that describes the outline of targets and present
results of our research project. Problems on volcanic information and education for
mitigation of volcanic hazards fairly became clear by a workshop and educational
activity. Present results on new tools applied for volcano monitoring at active
volcanoes in southern Kyushu are described; geomagnetic observation, remote sensing
for volcanic gases, and so on. Basic concept of a system of information processing onseismic data is described.
Keywords: Volcanic information; Volcano monitoring; Information processing

1. Introduction
There are 108 active volcanoes in Japan, and 5
volcanoes have erupted on average, and several
volcanoes indicate abnormal activity each year.
Among them, 3 to 4 volcanoes have induced severe
hazards or threatened people every decade, e.g.
eruptions at Unzen volcano (1991-1994), Usu
volcano (2000) and Miyakejima volcano (2000-) andvolcano-seismic crisis at Iwate volcano (1998). Since
eruption ejects huge amount of volcanic materials
and completely destroys everything around a volcano,people must evacuate from hazardous zone to safetyarea before eruption. Therefore, forecasting of
volcanic eruptions, volcanic hazard maps, and planfor volcanic disaster prevention are essential tools for
mitigation of volcanic disasters.
In Japan, the Japan Meteorological Agency(JMA) has responsibility for volcano monitoring andhas issued volcanic information to publics in volcano
crises. To cover insufficient ability of JMA in
volcano monitoring and evaluation of volcanic
activity, the Coordinating Committee for Predictionof Volcanic Eruptions (CCPVE) was organized in
1974. Universities, Coast Guard, and otherinstitutions are the members, and CCPVE has
evaluated significant volcanic activity and given
statements which have been announced as volcanic
information of JMA. This system has worked
effectively in case of the 2000 eruptions at Usu andMiyakejima volcanoes, where volcanic alerts were
issued just after detection of significant earthquake
swarms, and people evacuated in safety area before
the onset of eruptions.
Miyakejima and Usu volcanoes are rather
exceptional, because most of Japanese volcanoes
indicate no significant seismic precursors just before
eruptions, and it is difficult to evaluate volcanicactivity only by seismic data and to issue clear
statement on the possibility of eruptions. At present,
local governments and people at most volcanoes are
urged to respond volcanic crises, accepting
incomplete and ambiguous volcanic information.
In this study, we will treat two topics. The firstone is related to volcanic information and public
education for mitigation of volcanic disaster. The
second one is improvement in quality and ability ofprediction of volcanic eruptions, e.g. new methods of
volcano monitoring and evaluation method of
volcanic activity, including quick information system
on volcanic activity. In this paper, we will report
the outline of research activity during past 2 years.
2. Volcano information and public education
2.1 Workshop on volcanic information
On March 11, 2003, ‘Sakurajima Workshop on
Information for Mitigation of Volcanic Hazards’
supported by 21stCentury COE program for DPRI,
Kyoto University, was held at Sakurajima,
Kagoshima (Ishihara ed., 2003). The main purposesof the workshop are to exchange knowledge andexperiences in recent volcano crises at Usu, Iwate,
Miyakejima, and Suwanosejima volcanoes, and toclarify problems related to volcanic information andresearch topics in near future. 65 participants camefrom JMA, local governments, universities, Japan
Coast Guard, Ministry of Land and Transportation,
mass media and institutions. Totally 14 papers were
presented.
[1] Revised definition and classification of active
volcanoes in Japan, based on their past activity(Uhira, JMA-Headquarter)[2] Volcano information and effective communication among disaster prevention organizations in the2000 eruption of Usu volcano (Miyamura, JMASapporo)[3] Volcanic disaster of the 2000 Usu eruption andresponse of autonomy (Tanabe, Sobetsu Town
Office)[4] The point of hazard mitigation at Usu volcano:Support for communities through communication(Okada, Hokkaido Univ.)[5] Volcano information and countermeasure for the
volcanic unrest at Iwate volcano since 1998
(Yoshikawa, JMA-Sendai)[6] Mitigation of volcanic hazards and response doneby universities (Hamaguchi, Tohoku Univ.)[7] Volcano information and monitoring of Miyakejima volcano (Usui, JMA-Tokyo)[8] Response of Tokyo Metropolitan Governmentand relationship with volcanologists for the 2000
Miyakejima eruption (Sasai and Miyazaki, Tokyo
Metropolitan Gov.)[9] Volcanic activity and volcanic information at
Suwanosejima volcano in 2002 (Hiramatsu, JMAFukuoka)[10] Volcano information and alert level of

Sakurajima volcano (Daiku et al., JMA-Kagoshima)[11] Volcanic processes of large eruptions andinformation at Sakurajima (Ishihara, Kyoto Univ.)[12] Investigation on alert level of active volcanoes
in Japan –Present and future view- (Yamasato, JMAHeadquarter)[13] User requirements on volcanic information(Hayashi et al., JMA-Headquarter)[14] Requests on volcanic information from local
governments (Higashi, Kagoshima Prefecture Gov.)
Summary of active discussion are as follows:(1) Contents and essential parts of ‘Volcanic
information’ are not easy to understand for staff oflocal governments and people. Who are the users of
volcanic information? And to whom issue of volcanic
information is oriented? Detail explanation should
be done by JMA, and lesson on volcanological terms
is expected to staff of local governments andresidents at active volcanoes.
(2) Local governments expect to get ‘additional
information and advice’ from volcanologists ofuniversities. They need the other line of informationin addition to volcanic information from JMA.
(3) ‘Alert level of volcanic activity’ which will besoon applied by JMA to 5 volcanoes was appreciatedby most of participants. Application to othervolcanoes and is expected, after negotiation on thecriteria of alert level with related autonomy is done.
(4) Communication systems among residents, local
government, scientists and so on at volcanoes areimportant for mitigation of volcanic hazards.
2.2 Practical Public Education
Daisuke Fukushima, a COE researcher, hascontinued practical activity to get procedures on how
to stimulate interest of residents toward Sakurajima
volcano and how to transfer knowledge for mitigationof volcanic hazards, based on ‘Ecomuseum’ concept(Fukushima and Ishihara, 2004).
His activity
includes lectures for students and adults, lecture andfield tours for member of Sakurajima Friend
Association organized by him.
He collected
questionnaire from attendants and analyzed it. He
temporarily got some conclusions. Lecture andeducation directly oriented to hazard mitigation are
not necessarily effective. Combined program of
lectures with field tours are more effective foreducation on disaster, and the contents of the
program should include culture and nature of
Sakurajima.
3. Development of evaluation method of volcanic
activitySouthern Kyushu is the most active volcaniczone in Japan (Fig.1). Both Sakurajima and
Suwanosejima volcanoes have intermittently erupted
for about half a century. Satsuma-Iwojima has
emitted continuously huge amount of volcanic gases
over one thousand years, started emission of volcanic

Kaimon

Univ.

−

885

Satsuma-Ionia

JMA, Univ.

Published

1998〜

Kuchinoerabujima

Univ.

Published

1980

Nakanoshima

Univ.

Published

1949

Suwanosejima

JMA, Univ.

Published

1949〜

flows. The 1966 eruption was followed several
minor eruptions until 1980. Sakurajima Volcano
Research Center started seismic observation in 1992
using an interactive personal computer system(Iguchi, 1991), as eruption potential is expected toincrease in a decade. Volcanic earthquakes haveactually increased since July 1999 (Fig.2).
Joint Observation by universities was carried out
in 2000-2001 to get baseline data on seismic,
geodetic, geomagnetic, geothermal and geochemical
observation (Sakurajima Volcano Research Center,2002). Most of observation data and results ofresearch suggested consistently that the storage oferuption energy might be located 0.5-1 km under thesummit crater, e.g. location of micro-earthquakes wasconcentrated at a zone shallower than 1 km under thecrater and no earthquakes deeper part. It was also
recognized that seismic and geodetic data are notenough to evaluate eruption potential for phreatic
explosions, and geomagnetic and geochemical
observation are required to be continued to detect
geothermal state under the volcano.
Continuous observation of geomagnetic force
around the summit crater was initiated using satellite
telecommunication in late of 2000 (Kanda et al.,2001) and the method of data processing is developed(Kanda and Fujii, 2003). Geomagnetic changes at a
rate of a few nT/y started in the mid of 2001, whichsuggested demagnetization of volcanic body at a
depth shallower than 1km due to temperature
increase, probably, up to 400 ℃ or more． The rateof geomagnetic changes at stations around the craterhas been accelerated up to 10 nT/y since January
2003. Then new fumaroles appeared on the wall of
the summit crater in February, and CO was detectedin volcanic gases, which suggested temperature in thesubsurface of the summit area increased significantly.
Volcanic processes of the volcano are summarized asfollows:
1) 1991-June, 1999: Normal state2) Mid of 1999- mid of 2001: Temporal increase ininternal pressure at shallow part indicated by seismic
and GPS data
3) Mid of 2001-December 2002: Temperature
gradually increased under the crater suggested bygeomagnetic changes and gradual increase inseismicity.
4) January 2003-: Hydrothermal system under thecrater has been activated indicated by new fumaroles
and temperature increase on the crater wall,
acceleration of geomagnetic change and change inchemical components of volcanic gases.

2.1 Research on the evaluation of eruption
potential at Kuchinoerabujima volcano.
Kuchinoerabujima volcano originated strong
phreatic explosions in 1841, 1931, 1933 and 1966.
Many residents were killed and some communities
were destroyed completely by eruptions and mud

Thus it was revealed that geomagnetic
observation is powerful tool to evaluate geothermal
state at shallow part of active volcanoes. However,
it is still unsolved problem how to evaluate
quantitatively heat energy accumulated under thecrater from the data of geomagnetic changes, andwhether phreatic explosions is triggered mainly byash in 1997. Kuchinoerabujima volcano, which
repeated strong phreatic explosions, indicated gradualincrease in volcanic activity.
Thus, southern
Kyushu is the best test field to develop monitoringand evaluation methods on volcanic activity. In
addition,
Kagoshima
prefecture
government
published volcanic hazard maps and made plan for
mitigation of volcanic hazards for these volcanoes(Table 1).

.
Fig.1 Active volcanoes in southern Kyushu. Open
triangles are those added as active volcanoes byrevised definition of active volcanoes in 2003.

Table 1 Monitoring and hazard maps at volcanoes in
Kagoshima prefecture
VolcanoMonitoring

Hazard map

Last eruption

Kirishima

JMA, Univ.

Published

1991

Sakurajima

JMA, Univ.

Published

1955〜the heat energy accumulation or excited by additional
intrusion of magma.
Residents reported that they recognized volcanic
rumblings or weak earthquakes immediately before
some of former explosions. To forecast eruptions, weneed both quick information processing of seismic
data and information on abnormal phenomena fromresidents.

350
300
250
200
150
100
50
Jan.2004

Jan.2003

Jan.2002

Jan.2001

Jan.2000

Jan.1999

Jan.1997

Jan. 1998

Jan.1996

Jan.1995

Jan.1994

Jan. 1993

Jan. 1992

0

Fig.2 Monthly number of volcanic earthquakes at
Kuchinoerabujima volcano
2.2 Geochemical tools for monitoring of volcanic
gases and volatiles in magma
Monitoring of gas flux and gas components from
active volcanoes and evaluation of volatiles inmagma are considered as the most important tools forevaluation of volcanic activity and forecasting
volcanic eruptions for geochemists, since most of
eruptions are excited by gases dissolved from magma.
Recently, a new portable instrument formeasurement of SO2 emission is produced;
differential optical absorption spectrometer (DOAS).
The size, weight and consumed electric power of
DOAS are much smaller than the former type, that is,
COSPEC (Correlation spectrometer), as brought andoperated by a single person at volcanoes. Takeshi
Mori, a COE researcher, made experimental
observation at Sakurajima and Suwanosejima tocheck its performance of instrument and reliability ofobtained data with colleagues (Mori et al, 2004).
There are no significant difference in data between
DOAS and COSPEC and also no discrepancy in data
among three sets of DOAS. It is also verified bycontinuous monitoring for several hours performed at
the summit of Suwanosejima that DOAS is useful forobservation of temporal changes in SO2 emission
rate.
Volatile components trapped into volcanic ash
particles were analyzed, using ash samples of
Sakurajima collected by SVRC during the past 30
years, and compared with eruption styles. Volcanicash emitted during swarms of B-type earthquake
contained higher amount of chlorine than that emitted
by explosive eruptions. This supports the hypothesis

derived from geophysical observation that swarms of
B-type earthquakes might be originated by extrusionof fresh magma (Ishihara and Iguchi, 1989).

2.3 Development of an automated information
system on volcanic earthquakes and activity
It is well known that volcanic earthquakes andtremors observed at active volcanoes are classified
into several types, and predominant types of seismic
events change with the progress of volcanic activity，
including amplitude and number of volcano-seismic
events. Classification of volcano-seismic eventsand statistical evaluation of the data is useful forforecasting volcanic eruptions (e.g. Nishi, 1984;
Hidayati et al, 1998). Nishi (1988) proposed anddeveloped a prototype of automated data processing
system for volcanic earthquakes. It is composed of
two parts: the one is classification of seismic eventsusing several parameters and the other one isstatistical evaluation of volcanic activity. The main
parameters using classification are[1] Arrival times of triggered events[2] Maximum amplitudes[3] Spectra of seismic waves[4] Duration[5] Amplitude of air shocks, and combined parameters among seismic stations.
Using these parameters, each event was classified
into ‘A-type earthquakes’, ‘B-type earthquake’,‘Explosion’, ‘Eruption’, ‘Volcanic tremor’, ‘C-type
tremor’, ‘Debris flow’ and ‘Not volcanic’. He tried
to evaluate statistically the possibility of explosions
in next 24 hours, using the data of B-type
earthquakes. The results were partly satisfactory fora short time, but not necessarily acceptablethroughout a long time, because the quantitative
relationship between B-type earthquakes andexplosions changes with stage of activity. Later,
more reliable forecasting system, ‘AutomatedWarning System for Summit Explosions’ wasdeveloped using deformation data (Kamo andIshihara, 1989), and the system has been used by
Kagoshima Meteorological Observatory.
Volcano monitoring system at Sakurajima
Volcano Research Center (SVRC) has expanded toisland volcanoes in Kyushu (Fig. 1). New seismic
data processing system is now being developing,based on Nishi’s trial. The concepts and purpose
are, however, different from his idea. The purpose
is not ‘forecasting eruptions’ but ‘informing levels of
volcanic activity’ to researchers working at volcanoes,
volcano experts, autonomies and others.
Theoutline of the concept is illustrated in Fig. 3.
(1) Classification of seismic events at each volcano isdone in a similar way as Nishi did, though types ofseismic events at each volcano are differ from thoseat other volcanoes.
(2) Short daily reports are regularly transmitted toresearchers and others by hand-phones or e-mails.
Detail data are accessible through internets. Whenearthquake swarm or large earthquakes are detected,
rapid reports are transmitted.
(3) Information of three levels is in consideration: forvolcano experts [level A], for governmental use[level B], and for residents [level C].
Now, this system is in test operation at SVRC. We
have several problems to be solved on practical useof this system, e.g. check of result of classification of
volcanic earthquakes, criteria for evaluation of
eruption potential and some technical problems.

Fig.3 Concept of information system on volcanic
activity
4. Concluding Remarks
It became fairly clear through the workshop andpractical activity on public education; what people
expect for volcanic information and how we should
transfer knowledge on mitigation of volcanic hazards.
Some tools were newly put into volcano monitoring
and a system of information processing on volcanic
data was introduced. It is our task in this project toimprove the evaluation methods of volcanic activity
from volcanological point of views, and to develop
the information system useful for mitigation of
volcanic hazards.

Acknowledgments
This research was supported by the Japanese
Ministry of Education, Culture, Sports, Science andTechnology (MEXT) 21st Century COE Program for
DPRI, Kyoto University (No.14219301, Program
Leader: Prof. Yoshiaki Kawata) as well as the Grantin-Aid for Scientific Research (specially promoted
research) (2) (No. 14080205, Principal Investigator:
Y. Tanaka, Kyoto University) and DPRI Joint
Research Project (15G-09, Principal Investigator, K.
Nogami, Tokyo Institute of Technology).
References
Fukushima, D. and Ishihara, K. (2004): Practicalresearch on educational dissemination for volcanic
disaster prevention: A case study based on the
ecomuseum concept, Annuals of DPRI, Kyoto Univ.,
No. 47, C (this issue).

Iguchi, M. (1991): Geophysical data collection using
an interactive personal computer system (part 1),
Bull. Volcanol. Soc. Japan, Vol. 36, pp. 225-343.
Iguchi, M., Yamamoto, K., Takayama, T., Maekawa,T., Nishimura, T., Hashino, H., Yakihara, H. andHirano, S. (2002): Characteristics of volcanic
earthquakes at Kuchinoerabu volcano-Geophysicaland Geochemical Joint Observation 2000-, Annualsof DPRI, Kyoto Univ., No. 44, B-1, pp. 317-326 (inJapanese).
Ishihara, K. and Iguchi, M. (1989): The relationshipbetween micro-earthquake swarms and volcanic
activity at Sakurajima volcano, Annuals of DPRI,
Kyoto Univ., No. 32, B-1, pp. 1-11 (in Japanese).
Ishihara, K. (ed) (2003): Report of Workshop on
Volcanic Information, 21stCentury COE programfor DPRI, Kyoto University, 50 p. (in Japanese).
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experiment on automated judgment of the stages of
eruptive activity using tiltmeter records at
Sakurajima, Japan, IAVCEI proceedings in
Volcanology 1, Volcanic Hazards, pp. 585-598.
Kanda, W., Tanaka, Y., Utsuki, M, Iguchi, M. and
Ishihara, K. (2001): Monitoring geomagnetic total
intensity using satellite telecommunication at
Kuchinoerabujima volcano, Annuals of DPRI,
Kyoto Univ., No. 44,B-1, pp. 327-332 (in Japanese).
Kanda, W. and Fujii, I. (2003): An attempt to detect
the volcanomagnetic variation by a Kalman filter
algorism, Annuals of DPRI, Kyoto Univ., No. 46, B,
pp. 797-803 (in Japanese).
Mori, T., Ishihara, K., Hirabayashi, J.., Kazahaya, K.
and Mori, T. (2004): SO2 gas monitoring by DOAS
at Sakurajima and Suwanosejima volcanoes,
Annuals of DPRI, Kyoto Univ., No. 47, C (thisissue).
Nishi, K. (1984): Volcanic B-type earthquake swarm
preceding volcanic explosion, Annuals of DPRI,
Kyoto Univ., No. 27, B-1, pp. 29-34 (in Japanese).
Nishi, K. (1988): An automatic data processing
system for volcanic monitoring, Proceedings,
Kagoshima International Conference on Volcanoes,
pp. 250-253.
Sakurajima Volcano Research Center (ed.) (2002):
Report on Joint Observations at Satsuma-Iwojima
and Kuchinoerabujima Volcanoes 2000, Sakurajima
Volcano Research Center, DPRI, Kyoto University,
184 p. (in Japanese).
Hidayati,S., Iguchi, M., Ishihara, K., Purbawinata,
M.A., Subandoriyo, Sinulingga I.K. and Suharna(1998): A preliminary result of quantitativeevaluation on activity of Merapi volcano, Proc.
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要旨ワークショップの開催，実践的な教育・普及活動に取り組み，火山防災情報の質の向上にかかわる問題点の整理がかなり進んだ．また，火山活動の評価手法を目指して，薩南諸島の火山において地磁気の連続観測，近年開発されたDOASによる二酸化硫黄の放出率の測定等を行い，また，過去30年間の桜島の火山灰中の揮発成分の分析を行い，他の観測調査データ等と比較することによって，これらの観測・分析手法が火山活動評価や噴火機構研究の有効なツールとなりうることを確認した．さらに，複数の火山の火山性地震を自動分類し，その結果を必要に応じて携帯電話やE‑mailで関係者に通報するシステムを開発し，試験運用を開始した．
キーワード: 火山防災情報，火山観測手法，自動データ処理，情報伝達

火山活動の評価手法の開発と火山防災情報に関する研究（序報）○

石原和弘

１．はじめにわが国には，108 の活火山があり，毎年平均５火山で噴火が発生し，ほぼ同数の火山で異常現象が発現している．また，顕著な災害を引き起こす火山活動は，十年間に３〜４火山で発生している．約 30 火山では，ハザー
ドマップなどが作成・公表され，火山災害に対する対応を地域防災計画で定めている．特定の火山では，噴火の直前予知と対応には実績があるものの，数多くの火山ではいまだその段階には達しておらず，噴火様式の予測などについては，未だ困難である．わが国では，気象庁が火山活動の監視と火山情報の発表の責務を負い，自治体が住民の安全確保の責任を負っている．本研究では，火山活動の評価手法の開発と，情報伝達にかかわる諸課題の解決に向けた取り組みに焦点をあてた．

２．火山防災情報に関する研究（１）火山防災情報ワークショップ in 桜島
2003 年 3 月，全国の大学，気象庁，自治体，防災関係者が集合し，火山活動のレベル化，活火山の見直しな
どの新たな動き，有珠や三宅島などの危機時の火山情報と自治体等の対応について議論し，平常時・危機時の火
山防災の取り組みと火山情報のあり方について討議した．
（２）火山防災のための教育・普及活動
COE 研究員福島大輔（COE12 参照）は，火山防災の意識を住民・行政に根付かせるにはどのような取り組みが必要か探るため，講演，出前授業，野外研修などさまざまな活動を行い，教育普及活動のあり方を模索している．

３．火山活動評価手法の開発（１）水蒸気爆発の発生過程
長い休止期間の後の大規模噴火は，水蒸気爆発から始まる例が多く，その発生過程・機構の理解は火山噴火予知の重要課題のひとつである．20 世紀に顕著な水蒸気爆発を繰り返し，近い将来において噴火発生の可能性の高い口永良部島を対象に，水蒸気爆発の発生過程の解明を目的として，各種の調査・観測を行ってきた．その結果，山頂火口の地下浅部で，エネルギーの蓄積が緩やかではあるが着実に進んでいることが，地震，地殻変動，
地磁気，地温，火山ガスなどの観測によって捉えられた．
（２）火山ガス，マグマ中の揮発成分
近年開発された二酸化硫黄濃度の小型軽量な遠（DOAS）を用いた火山ガス中の二酸化硫黄放出率の試験観測を，
COE 研究員森健彦らが諏訪之瀬島，桜島等で実施した．従来の装置（COSPEC）と整合する測定値が得られる
こ，また，活動中の諏訪之瀬島で連続観測を実施し，噴火機構解明に有益な顕著な二酸化硫黄の濃度の時間変化のデータを得た．野上他は，桜島の火山灰中の塩素濃度が噴火様式の間で変化することを見出した．
（３）火山活動度の自動評価システムの開発
火山活動研究センターでは，南九州の５火山の火山性地震・微動の自動分類装置の開発に着手した．活火山を調査する観測者・研究者や住民の安全確保を図るため，分類結果をもとに火山活動を評価して，異常を検知したとき，携帯電話やインターネットを介して，防災関係者に通報するシステムへと発展させたいと考えている．