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Unrest that led to eruption: Unzen and Kirishima, Japan

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1 Unrest that led to eruption: Unzen and Kirishima, Japan
Volcano Observatory Best Practice Workshop - Near Term Eruption Forecasting Erice, Sicily (IT), 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

2 Eruption history at Mount Unzen
: 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. : 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

3 Precursor of eruption (seismicity)
Nov. ‘89 Dec. ‘89 Nov. 19, 1990 July ‘90 Oct. ‘90

4 Precursors of first eruptions
Earthquake Volcanic Tremor Micro-pumice in phreatic eruption products in February 1991 May 3, 1991

5 Precursors of lava dome emergence
These were reported to the Coordinating Committee for Prediction of Volcanic Eruptions (CCVEP) EDM Ground tilt Magnetic total Force May 20, 1991

6 GPS at Unzen Nishi et al, (1999) JVGR v.89

7 Transmission of volcanic information in Japan
JMA only can issue official statements on volcanic activity. Japan Meteorological Agency (JMA) Coordinating Committee for Prediction of Volcanic Eruptions (CCPVE) JMA Observatories of universities National Institutes Local government Mass media The public / concerned inhabitants Volcanic Information Monitoring data Volc. Inform. Observation data/results are reported to CCPVE which assesses the unrest. Volcanic information is transmitted to The public through local government/ mass media.

8 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 /The June 3rd pyroclastic flow had been largest by that time. /Fireman and fire car were running away from cloud of pyroclastic flow. /They could escape from the attack. /After passing of pyroclastic cloud, large trees are completely cut down, but this is only the pathway of cloud of pyroclastic flow. June 24, 1993 June 3, 1991

9 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.

10 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) Local governments Mass media Unofficial information (real-time) Comments Self Defense Force Shimabara Observatory Mass media Inhabitants Police Advices Local government Cable TV Unofficial information (real-time)

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

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

13 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

14 Eruption at Shinmoedake (Kirishima) in 2011
IUGG (Melbourne) on July 4, 2011 Today’s my talk is on the newest volcanic eruption in Japan which started at Kirishima volcano this January. The background photo of this slide shows the subplinian explosion of January. Volcanic ash was drifted eastward, so that several airplain flights were cancelled or forced to detour from the normal flight courses. Eruption at Shinmoedake (Kirishima) in 2011 Jan.26 pm (Courtesy by Kazuo Shimousuki)

15 Location of Kirishima Volcano Group
Pumice eruption in Shinmoedake crater after about 300 yrs silence. In , plinian explosions with pyrolcastic flows continued for two years Kirishim locates in southern Kyushu and north of Sakurajima. It is a group of volcanoes, including two most active centers; one is Ohachi and Shinmoedake. Eruption occurred in Shimoedake. Pumice eruption occurred in Shinmoedake about 300 years ago. The January eruption was reproduction of pumice eruption. Shinmoedake Ohachi

16 Three sub-plinian explosions in Jan. 26 and 27, 2011
Jan 26 evening The explosion continued for a few hours. Height of ash column was 7-9 km above the crater. In the downwind side, small scale pyroclastic flow was generated. Courtesy by Kazuo Shimousuki Jan 27, 15:41 explosion

17 Lava accumulation in crater for Jan. 28-31, 2011
The lava dome grew rapidly and it filled the crater in the following 4 days. During the growth very beautiful growing rings or wrinkles were observed on the surface. The form of this lava accumulation was flattened when the magma supply declined. Explosion crater was sealed with new lava. Taken by Tetsuo Kobayashi on Jan 31, 2011

18 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. The lava growing manner could be clearly followed by satellite SAR images. This is the example of lava accumulation within the crater. Growing wrinkles of lava surface is clearly visible. This kind of image was very effective to give warning to the local people. That is; the rate of lava accumulation was very fast, covering the explosion craters, so that we worried about imperfect degassing which may trigger sudden explosion. TerraSAR-X Entered into vulcanian stage Courtesy by PASCO Co., Ltd.

19 Strain change & magma volume
Vulcanian St. Subplinian explosions Lava accum. stage Direction toward the source Normal direction toward the source The extensometer and tiltmeter records were too important during explosions. This shows data of extesometer near the volcano. Before the onset of explosion, the data show daily drift. When subbplinian explosion occur the deflation of summit area marked. Three deflation crealy match the time of explosions. During lava accumlation at the crater, slow deflation was recorded continuously. As we can know the volume of lava accumulated in the crater with photographic measurement, we can know how much magma was issued during eruption by using the relationship between the extent of deflation and erupted magma volume.. The total volume of eruption ranges 21 million cubic meters in geological estimation. And the volume of magma which can be calculated from the extensometer is close to the geological value. Methods Tephra DRE, x104 m3 Lava accum. Total DRE, Deposit 730~ 1100 1400 2100 ~2500 Strain 1300 1400* 2600 Data of extensometer (Isa Observation Station of DPRI, Kyoto Univ.)

20 Eruption rates change Lava accum. St Vulcanian St.
Plinian St. Lava accum. St Vulcanian St. As we know the duration of each explosion or lava accumulation, we can calculate the eruption rates. This diagram shows the temporal change of eruption rate. The rate of subplinian explosion ranges 0.5 to 1.5 million kg per second. These values are typical to the eruption rate of typical subplinian explosions. Typical subplinian Shinmoedake 2011 Intensity ~106 kg/s Magnitude ~1011 kg x1010 kg Column height <20 km 7-9 km Typical subplinian explosion data from Cioni et al. (2000)

21 Temporal change in seismicity in Kirishima Volcano
Yakiwara and others (2011) 2001/01/01 to 2011/06/30 3,401 The rate increased with time Earthquakes The rate increase in mid-2006 and the end of 2009.

22 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

23 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. Juvenile materials were found in the products of phreatic eruptions a week before the first subplinian explosion.

24 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.

25 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.

26 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 Dates Aug. 22, 2008 Mar-Jul. 2010 2011 Jan. 19 Jan Jan 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) This was established in order to take rapid response to the public based on the agreement between JMA and local municipalities.

27 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)

28 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.

29 Present condition of Shinmoedake
GPS Daily cumulative time of volcanic tremor hrs SO2

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