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Volcano Observatory Best Practice Workshop - Near Term Eruption Forecasting Erice , Sicily (IT), 11 - 15 September 2011. Unrest that led to eruption: Unzen and Kirishima , Japan. Setsuya Nakada 1 and Hiroshi Shimizu 2

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Unrest that led to eruption unzen and kirishima japan

Volcano Observatory Best Practice Workshop

- Near Term Eruption Forecasting

Erice, Sicily (IT), 11 - 15 September 2011

Unrest that led to eruption: Unzen and Kirishima, Japan

Setsuya Nakada1 and Hiroshi Shimizu2

1. Volcano Research Center, Earthquake Research Institute, The University of Tokyo

2. Institute of Seismology and Volcanology. Kyushu University

Eruption history at Mount Unzen

  • 1663 - 1664: More than 30 people were killed by earthquakes and

  • debris flows.

  • 1792: Failure of Mt. Mayuyama(old lava dome) generated tsunami.

  • About 15,000 people were killed.

  • 1990 - 1995: Lava effusion continued for almost 4 years.

    • (2x108m3 ofdacite lava was extruded)

  • 44 people were killed by pyroclastic flows.

  • About 2,500 houses were destroyed.

  • Mt. Fugen-dake

    (Main Peak of

    Unzen Volcano)

    Mt. Mayuyama

    Shimabara City

    Nov. ‘89

    Dec. ‘89

    July ‘90

    Oct. ‘90

    Precursor of eruption (seismicity)

    Nov. 19, 1990

    Precursors of first eruptions


    Volcanic Tremor

    Micro-pumice in phreatic eruption products in February 1991

    May 3, 1991

    Precursors of lava dome emergence

    These werereported to the Coordinating Committee for Prediction

    of Volcanic Eruptions (CCVEP)


    Ground tilt


    total Force

    May 20, 1991

    Gps at unzen
    GPS at Unzen

    Nishi et al, (1999) JVGR v.89

    Japan Meteorological Agency (JMA)

    Coordinating Committee for Prediction of Volcanic Eruptions (CCPVE)








    The public /

    concerned inhabitants


    of universities

    Transmission of volcanic information in Japan

    JMA only can issue official statements on volcanic activity.

    Volcanic Information



    Volc. Inform.

    Volcanic information is transmitted to

    The public through local government/

    mass media.

    Observation data/results are reported to

    CCPVE which assesses the unrest.

    Pyroclastic flow event

    The Yomiuri

    Pyroclastic flow event

    • Dome collapse started on May 24, 1991

    • Pyroclastic surges attacked mass media and fire station staffs. June 3, 1991

    June 24, 1993

    June 3, 1991

    The prefectural governor asked the Self Defense Force (SDF) for rescuing casualties.

    The operation in a limited area needed real-time information on volcanic activity.

    Other civil protection agencies also needed real-time information for quickly respond to coming disaster.

    The official information flow was too slow during pyroclastic flow events.

    Transmission of volcanic information at Unzen Volcano

    Cooperation between organizations concerned made it possible to transmit unofficial but useful volcanic information: more quickly, accurately and understandably.

    Official information

    Japan Meteorological Agency

    Coordinating Committee for Prediction of Volcanic Eruptions (CCPVE)





    Unofficial information (real-time)












    Local government

    Cable TV

    Unofficial information (real-time)

    Members of SDF and police stationed at the observatory (SEVO),

    watching seismograms and video monitors all day.

    They transmitted the monitoring data directly to their headquarters.

    The information was shared with the local government and cable-TV.




    SDF, police, local governments and inhabitants were able to be informed immediately what was monitored.

    Daily observation flight by SDF-helicopter

    In addition,volcanologists shared the observation data to SDF, police, local government and mass media soon after helicopter flights every day.

    Prof. Ohta

    Local government official


    Mass media

    Mass media braodcasted volcanologists’ comments soon after the daily inspection flight.

    SDF supported volcanologists in helicopter flights, Doppler radar observation, and maintaining the observation system within the limited areas.

     Doppler radar was used to know the travel distance of pyrolastic flows

    Eruption at shinmoedake kirishima in 2011

    IUGG (Melbourne) on July 4, 2011

    Eruption at Shinmoedake (Kirishima) in 2011

    Jan.26 pm

    (Courtesy by Kazuo Shimousuki)

    Location of kirishima volcano group
    Location of KirishimaVolcano Group


    Pumice eruption in Shinmoedake crater after about 300 yrs silence.

    In 1715-16, plinian explosions with pyrolcastic flows continued for two years



    Three sub-plinian explosions in Jan. 26 and 27, 2011

    Jan 26 evening

    Courtesy by Kazuo Shimousuki

    Jan 27, 15:41 explosion

    Lava accumulation in crater for Jan. 28-31, 2011

    Explosion crater was sealed with new lava.

    Taken by Tetsuo Kobayashi on Jan 31, 2011

    SAR images with a few days interval were very effective

    Explosion crater was covered completely with new lava


    Insufficient degassing


    Highly possible strong explosions


    This observation data were not reflected to evacuation plan.


    Entered into vulcanian stage

    Courtesy by PASCO Co., Ltd.

    Strain change & magma volume

    Vulcanian St.






    Direction toward the source

    Normal direction toward the source

    Data of extensometer (Isa Observation Station of DPRI, Kyoto Univ.)

    Eruption rates change

    Plinian St.

    Lava accum. St

    Vulcanian St.

    Typical subplinian explosion data from Cioni et al. (2000)

    Temporal change in seismicity in Kirishima Volcano

    Yakiwara and others (2011)

    2001/01/01 to 2011/06/30


    The rate increased with time


    The rate increase in mid-2006 and the end of 2009.

    Temporal changes of GPS baselines

    Graphs after reducing the effects of vapor in air and regional tectonic movement.

    Geogr. Surv. Inst. (Data for 119th CCVEP)

    Inflation slowly during 2006 to 2007,

    accelerated after the end of 2009

    Pumice found in tephra of Jan 19 (0.5 mm across)

    Juvenile in tephra

    Phreatic explosions began in 2008, and repeated in 2010.

    10% of pumice were observed in the Jan 19, 2011 product, a week before sub-plinian explosions.

    Unzen 1
    Unzen (1)

    1. What kind of eruption forecasting assessment?

    Start of eruption (Nov 1990)

    1) Elevated seismicity and its migration

    2) Clear attenuation of seismic waves passing under the summit

    3) LP event that is the first time in monitoring at Unzen and increased.

    Lava appearance (May 1991)

    1) Swarm of high frequency B-type quakes beneath the crater

    2) Rapid changes in EDM and tilt-meter and shallow demagnetization

    3) Juvenile ash involved

    2. How the forecasts have been achieved?

    Couldn’t forecast exactly when steam explosion, but was expected.

    Lava effusion was forecasted by CCVEP.

    After lava effused (PF stage), rather qualitative assessment.

    Unzen 2
    Unzen (2)

    3. What kind or critical information was missed?

    The manual to issue the alert was not prepared 20 years ago. Probably better now…..?

    4. How the scientific forecast has been used to take mitigation actions (the decision-making chain)?

    After lava effused, the official information flow was not useful due to slowness.

    Instead, communication of observatory scientists with the local governments, mass media and army was effective.

    5. The interaction between scientists, decision makers, and mass media.

    Before lava effused, neither bad nor good.

    After lava effused, on-site interaction among them went well and timely.

    Volcanic warning introduced in 2007
    Volcanic warning introduced in 2007

    Alert levels in Shinmoedake (Kirishima)

    5: Evacuation

    4: Prepare for evacuation

    3: Limit approach to volcano (~2.5 km)

    2: Limit approach to crater area (~1km)

    1: Normal


    Aug. 22, 2008

    Mar-Jul. 2010


    Jan. 19

    Jan. 26-27

    Jan. 29-31

    Feb. 1-

    Volcanic phenomenon

    Phreatic explosion

    Phreatic explosions

    Magmatic eruption

    Sub-plinian explosions

    Lava accumulation

    Vulcanian explosions

    Volcanic Alert issued

    Aug. 22-Oct. 29, 2008: level 2

    Mar. 30-Apr. 16, Mar. 6, 2010: level 2

    Jan. 26: level 3 ~3km distance(bomb)..?

    Jan. 31: level 3 ~3km (pyroclastic flow)..?

    Feb. 1: level 3 ~4 km (bomb)

    Mar. 22: level 3 ~3 km (bomb/pyr. flow)

    Response was too slow
    Response was too slow

    • A village decided evacuation by themselves in the night of Jan. 30, 2011.

    • They lived within a few kilometers from the active crater, in the lowest side without seeing the crater. Explosions that night were so noisy for them to be very frightened.

    • In addition, effusion of “lava dome” was observed two days before. The word of “lava dome” made them to fall into a sort of panic, as they imaged pyroclastic flow events at Unzen by it.

    New lava dome in the crater floor (Jan. 28)

    Shinomedake kirishima
    Shinomedake (Kirishima)

    1. What kind of eruption forecasting assessment was made?

    1) Inflation rate increased for a year

    2) Rate of seismicity increased, though was not noticed correctly.

    3) Precursory steam eruption for a few years

    4) juvenile ash one week before the climax.

    2. How the forecasts have been achieved

    Forecast couldn’t be done correctly.

    3. What kind or critical information was missed?

    2) of 1 items. No one may have considered seriously.

    4. How the scientific forecast has been used to take mitigation actions?

    Personal scientific communication was useful in part.

    5. The interaction between scientists, decision makers, and mass media.

    Understanding and information issue were taken behind the phenomena.

    Present condition of shinmoedake
    Present condition of Shinmoedake


    Daily cumulative time of volcanic tremor