Unrest that led to eruption: Unzen and Kirishima, Japan

Setsuya Nakada1 and Hiroshi Shimizu2

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

Tokyo2. Institute of Seismology and Volcanology. Kyushu University

Volcano Observatory Best Practice Workshop - Near Term Eruption Forecasting

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

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.(2x108 m3 of dacite 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

Eruption history at Mount Unzen

Nov. ‘89 Dec. ‘89

July ‘90 Oct. ‘90

Nov. 19, 1990

Precursor of eruption (seismicity)

Micro-pumice in phreatic eruption products in February 1991

May 3, 1991

Earthquake Volcanic Tremor

Precursors of first eruptions

EDM

Ground tilt

Magnetic total Force

Precursors of lava dome emergence

These were reported to the Coordinating Committee for Predictionof Volcanic Eruptions (CCVEP)

May 20, 1991

GPS at Unzen

Nishi et al, (1999) JVGR v.89

Japan Meteorological Agency (JMA)

Coordinating Committee for Prediction of Volcanic Eruptions (CCPVE)

JMA

Observatoriesof universities

NationalInstitutes

Local government

Massmedia

The public / concerned inhabitants

Transmission of volcanic information in Japan

Observation data/results are reported toCCPVE which assesses the unrest.

JMA only can issue official statements on volcanic activity.

Volcanic information is transmitted toThe public through local government/mass media.

Monitoringdata

Volcanic Information

Volc. Inform.

Pyroclastic flow event• Dome collapse started on May 24,

1991• Pyroclastic surges attacked mass

media and fire station staffs. June 3, 1991

The Yomiuri

June 24, 1993June 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.

Japan Meteorological Agency

Coordinating Committee for Prediction of Volcanic Eruptions (CCPVE)

Local governments

Massmedia

Inhabitants

Transmission of volcanic information at Unzen Volcano

Official information

Massmedia

SelfDefense

Force

Police

Local government

Cable TV

ShimabaraObservatory

Unofficial information (real-time)

Unofficial information (real-time)

Advices

Comments

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

　　　　　　　　　　　　　　　　　　

SDFPolice

Volcanologist

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.

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

Mass media

Prof. OhtaLocal government official

SDF

Daily observation flight by SDF-helicopter

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

(Courtesy by Kazuo Shimousuki)

Jan.26 pm

Eruption at Shinmoedake (Kirishima) in 2011

IUGG (Melbourne) on July 4, 2011

Location of KirishimaVolcano Group

Kirishima

Shinmoedake

Ohachi

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

Courtesy by Kazuo Shimousuki

Jan 27, 15:41 explosion

Jan 26 evening

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

Explosion crater was sealed with new lava.

Taken by Tetsuo Kobayashi on Jan 31, 2011

Explosion crater was covered completely

with new lava|

Insufficient degassing|

Highly possible strong explosions

|This observation data were not reflected to

evacuation plan.

SAR images with a few days interval were very

effective

Courtesy by PASCO Co., Ltd.

Entered into vulcanian stage TerraSAR-X

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

Vulcanian St.Subplinianexplosions

Lava accum.

stage

MethodsTephraDRE, x104 m3

Lava accum.DRE, x104 m3

Total DRE, x104 m3

Deposit 730~1100 1400 2100

~2500

Strain 1300 1400* 2600

Normal direction toward the source

Direction toward the source

Strain change & magma volume

Typical subplinian

Shinmoedake 2011

Intensity ~106 kg/s ~106 kg/s

Magnitude ~1011 kg 0.3-1.5x1010 kg

Column height <20 km 7-9 km

Eruption rates change

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

Vulcanian St.Lava accum. St

Plinian St.

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 20110

1000

2000

3000

Cum

ulat

ive

num

ber

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 20110

1

2

3

4

Num

ber /

Day

Temporal change in seismicity in Kirishima VolcanoYakiwara and others (2011)

The rate increased with time

3,401

2001/01/01 to 2011/06/30

Earthquakes

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

Inflation slowly during 2006 to 2007,

accelerated after the end of 2009

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

Temporal changes of GPS baselinesGraphs after reducing the effects of vapor in air and regional tectonic movement.

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)1. What kind of eruption forecasting assessment?Start of eruption (Nov 1990)

1) Elevated seismicity and its migration2) Clear attenuation of seismic waves passing under the summit3) 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 crater2) Rapid changes in EDM and tilt-meter and shallow demagnetization3) 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)

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.

Alert levels in Shinmoedake (Kirishima)5: Evacuation4: Prepare for evacuation3: Limit approach to volcano (~2.5 km)2: Limit approach to crater area (~1km)1: Normal

Volcanic Alert issued

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

Volcanic phenomenon

Phreatic explosionPhreatic explosions

Magmatic eruptionSub-plinian explosionsLava accumulationVulcanian explosions

Dates

Aug. 22, 2008Mar-Jul. 20102011Jan. 19Jan. 26-27Jan. 29-31Feb. 1-

Volcanic warning introduced in 2007

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)

1. What kind of eruption forecasting assessment was made?1) Inflation rate increased for a year2) Rate of seismicity increased, though was not noticed correctly.3) Precursory steam eruption for a few years4) juvenile ash one week before the climax.

2. How the forecasts have been achievedForecast 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

SO2

Daily cumulative time of volcanic tremor

GPS

hrs