About 7 thousand people live at the foot of the volcano, and Kagoshima city with a population of about half a million is located 10 km west. The area within 2 km from the summit is "off-limit zone".

Explosive eruption with lightning at Sakurajima Volcano
Cinders were issued up to >2,500 m high (23:03 on18 May 1991; taken by SVO)

Sakurajima Volcano viewed from the east
Photo by International Air Photo Co.Ltd.

1. Characteristics of Volcanic Activity

   1. Andesitic volcano growing up at the south rim of the Aira caldera

   2. Repeated large flank eruptions (interval: 10^2 years) and summit eruptions (10^1 years)

   3. Production rate of magma during the historic time: (1-2)x10^10 kg/year

   4. Present state:

      a. Intermittent explosive eruptions and ash emission at the summit crater since 1955.

      b. Maximum range of flight of volcanic bombs: 3 km

      c. Maximum flow length of pyroclastic flows: 1.2 km

      d. Ashfall: 3 to 30 million ton/year)

      e. Debris flows caused by heavy rainfall, but almost controlled by Sabo engineering.

2. Volcano Monitoring

   1. Kagoshima Meteorological Observatory and Geomagnetic Observatory, Japan Meteorological Agency (JMA)

      Permanent observation: seismic. tilt, strain, sea level, air-shocks, video images, ashfall
      Survey: geomagnetic, water temperature

   2. Sakurajima Volcanological Observatory (SVO), DPRI, Kyoto University

      permanent: observation: seismic, tilt, strain, sea-level, geochemical, shock-wave, GPS
      survey: leveling, EDM, microgravity, etc.

   3. Kagoshima University

      Permanent observation: seismic, tilt
      Survey: EDM, GPS

   4. Kagoshima Prefectural Government

      Permanent observation: ashfall monitoring at 60 points

   5. Japan Air Line (JAL)

      permanent observation: seismic and air-shocks for aviation safety

   6. Joint Research by national universities

      Eight times since 1974, and the reports were published (written in Japanese)

   Data have been exchanged directly among institutions and agencies, and reported regularly at the Coordinating Committee for Prediction of Volcanic Eruption.
   

3. Volcanic Information

   1. Monthly and emergent volcanic information, and forecasting of wind direction above Sakurajima have been issued by Kagoshima Meteorological Observatory, JMA.

   2. The Coordinating Committee for Prediction of Volcanic Eruption has stated since 1974;

      a. The explosive activity will continue for the time being.

      b. There is no sign that the activity develops into large flank eruptions, and the precursor of flank eruption will be surely detected with volcano monitoring.
      

Public Work on Mitigation of Volcanic Disasters

1. Monitoring and mitigation of Debris flows: conducted by Osumi Construction Office, Ministry of Construction.

2. Drill of evacuation: conducted every year on 12 January (the memorial day of the 1914 eruption), using ferry boats, helicopters, aircrafts and so on.
   Organized by the prefectural government, town office, etc.

3. Volcanic hazards map: published and delivered in 1994.

4. Plan and system of evacuation: established and revised.
   

International Corporation

1. Experiment on detection and discrimination of volcanic ash clouds by infrared radiometry; CSIRO, Australia

2. Electrical and chemical properties of eruption plumes; university of Bristol and Lancaster University, UK

3. Isotopic study of volcanic rocks; Institute of Earth Sciences, Taiwan
   

Precursors of Eruptions and Method of Detection

1. Magma supply system of Sakurajima is characterized by (a) two magma reservoirs and (b) a constant magma supply at a rate of 10E7 c.m./year

2. Volcanic processes shallower than 10 km have been well monitored;

   a. Storage of magma beneath the caldera measured by leveling survey around the caldera (inflation of the caldera)

   b. Magma migration and storage beneath the volcano observed by tidal gauge and leveling survey at Sakurajima.

   c. A critical level of magma storage beneath the volcano or injection of magma from south of Sakurajima inferred from seismic observation (generation of A-type earthquakes)

   d. Rapid intrusion of magma into the shallow conduit after dormant periods detected by borehole seismometer, tiltmeter and extensometer (increase of BH-type earthquakes and gradual inflation of the summit)

   e. Extrusion of magma up to the summit crater detected by seismometers, infrasonic microphones, tiltmeters, and extensometers (swam of BL-type earthquakes, intermittent emission of air-shocks and deflation of the summit) --- indication that the preparation of explosive eruptions is completed ---

   f. Rapid injection of magma immediately before explosive eruptions evaluated from the date of tiltmeters and extensometers installed at an underground tunnel (inflation of summit)
   

Further Study

Three-dimensional structure of the caldera and volcano, interaction between two magma reservoirs, process in the magma conduit before and during explosive eruptions, geological evolution of the volcano, etc.

Go to Geology, Petrology, Geophysics at Sakurajima Volcano
Go to 1991-94 acitivity at Sakurajima
Go to Ash fall from Sakurajima (link to Kagoshima University)

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Go to Current eruptions in Japan
Go to Unzen Decade Volcano

If you have any comments and questions about this decade page, please feel free to e-mail them to: VRC-ERI, Univ. of Tokyo

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