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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 YomiuriPyroclastic 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

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