AIST (National Institute of Advanced Industrial Science and Technology)
GSJ (Geological Survey of Japan)
Miyake-jima Volcano
by A.Tomiya (Last revised: Aug 28, 2006)
[To Japanese page]
If you have any questions,
please ask "Geological Consulting Office" of GSJ.
E-mail : soudan@gsj.jp
Contents
- Present Status
- Photographs
- Summary of the 2000 eruption of Miyake-jima volcano
- About recent Miyake-jima eruptions (1940, 1962, 1983)
Present Status
[The gas emission and evacuation]
The volcanic activity of Miyakejima volcano since the 2000 summer is ongoing as of Aug 2006.
Much volcanic gas is still discharging.
The flux of SO2 gas is about 1,000 - 5,000 tons/day as of May 2006.
Although the gas flux is high, the danger of destructive eruptions is considered to be small.
The residents of Miyakejima island (ca. 3,800 people), who had been evacuated from Sep. 2000 to Jan. 2005, are now returning to their home island.
[The eruptions]
Very minor eruptions (small ash emission) sometimes occurs.
The last eruption occurred Aug 23, 2006 (as of Aug 28, 2006).
[list of eruptions since 2001]
Data from: The flux of Miyakejima volcanic gas (SO2) (by Japan Meteorological Agency)
#note: The "jima" (a euphonic change of "shima") in the word "Miyakejima" means "island", so that "Miyakejima" is the same meaning as "Miyake island".
[In addition, the word "miyake" is maybe originated from an honorific expression of "yake" (mi + yake), and the "yake" means "burning". If this is true, "Miyakejima" means "the burning island"! ]
Photographs
Selective photos of Miyakejima volcano (since Dec. 2000)
Recent Miyakejima volcano (Nov. 16, 2004)
(Sorry, Japanese only.)
Summary of the 2000 eruption of Miyake-jima volcano
Discolored seawater and magma intrusion: The events around 27 June
Water discoloration was found on 27 June about 1 km off the west shore of Miyake-jima, an island of Izu-Bonin islands. It was observed during the morning of the day, but vanished in the afternoon. No eruptive products were found for this activity.
Many fractures and three 'craters' were found on the seafloor near the discolored seawater by ROV (Earthquake Research Institute, Univ. Tokyo) and multi-beam side-scan sonar (Hydrographic Department, Japan Coast Guard). It is controversial, however, that there was an 'eruption'. Some researchers insist that it is only 'thermal water activity' activated by the magma that intruded near this region.
Many earthquakes have been observed since the evening of 26 June. The hypocenters were under the island at the first stage, but soon moved to west (observed epicenters by JMA). Now, the earthquake region is far west from the island (about 10km northwest).
Crustal deformation was also found, which implied the existence of open cracks under the west flank of the volcano.
Anyway, it is certain that magma intrusion occurred at the west flank of Miyake-jima volcano around 27 June. This intrusion caused the water discoloration and associated earthquakes.
Summit eruption and formation of a large pit crater (caldera): The events around 8 July
An eruption occurred at the summit of Miyake-jima on 8 July, following the earthquake swarm under the summit area since 4 July. The eruption was a very small phreatic explosion (the duration is only several minutes), and no essential material was ejected. In accordance with the eruption, a large pit crater was formed. The diameter is about 800m and the subsidence is about 100-200m. It is considered that the pit crater is caused by 'drain back' of the magma that intruded under the volcano, and that the eruption is induced by the collapse of the floor.
Enlargement of the crater (caldera)
The crater extended the size (both depth and diameter) for several weeks and by September 2000 its diameter reached about 1.6 km (about the same size today).
Now it should be called a "caldera".
(You can see data for the change of the size (in Japanese) by Geographical Survey Institute.)
Successive phreatomagmatic eruptions
Several phreatomagmatic eruptions occurrred during July and August, 2000 (July 14-15; August 10, 13, 18, 29).
The largest one occurred Aug. 18.
The following is the characteristics of the Aug. 18 eruption (e.g., Miyagi et al., 2000: Eos):
- the height of the eruption column was about 15 km;
- large amount of ash and bomb were ejected (ca. 7.5 million m3);
- the essential bomb was cauliflower-shaped (photo);
- about 30-40 % of the ash was essential fragment with many microbubbles and microlites (photo);
At the Aug. 29 eruption, low-temperature pyroclastic flow occurred.
The flow was weak, however, it reached the sea and its ash cloud ascended to 8000 m.
Large amount of gas emission with very minor explosions
After the largest eruption at Aug. 18, large amount of volcanic gas started to discharge.
The mean flux of SO2 during Sep. to Dec., 2000 was about 40,000 tons/day.
Large eruption has not occurred since Aug. 29, 2000, however, small explosions with minor ash emission sometimes occurred.
List of eruptions (small explosions) since 2001
Note:
All of the eruptions since 2001 are small with minor ash emission.
(Data from Japan Meteorological Agency)
| Date | Plume Height | Type | Time |
|---|
| [2001] | | | |
| Jan. 11 | 800m | - | at about 10:40 |
| Mar. 19 | 800m | - | at about 07:00 ~ 07:40 |
| May 27 | 1200m | M | at about 06:04 |
| Jun. 3 | 700m | - | at about 06:34 |
| Jun. 10 | 500m | - | at about 19:25 |
| Jul. 10 | 500m | - | at about 06:38 and 08:23 |
| Jul. 18 | ??? | - | at about 17:42 |
| Sep. 26 | 1000m | M | at about 11:32 |
| Sep. 27 | 1000m | M | at about 21:28 |
| Sep. 27 | 800m | - | at about 23:04 |
| Sep. 28 | 800m | - | at about 05:28 |
| Oct. 11 | ??? | - | at about 04:45 and 09:00 |
| Oct. 16 | 1500m | M | at about 07:22 |
| Nov. 1 | 800m | - | at about 12:32 |
| [2002] | | | |
| Jan. 23 | 200m | - | at about 12:34 |
| Feb. 21 | 300m | - | at about 17:37 |
| Mar. 2 | ??? | - | at about 05:53 and 06:12 |
| Mar. 31 | 200m | - | at about 06:04 |
| Apr. 2 | 300m | - | at about 10:02 |
| Apr. 16 | ??? | - | at about 06:00 |
| Jun. 15 | 500m | - | at about 16:19 |
| Aug. 1 | ??? | - | at about 17:42 |
| Sep. 16 | ??? | - | at about 05:10 |
| Oct. 8 | 200m | - | at about 14:51 |
| Nov. 24 | ??? | - | at about 13:20 |
| [2003] | | | |
| (There were no eruptions in 2003.) |
| [2004] | | | |
| Nov. 30 | 300m | - | at about 07:46 |
| Dec. 2 | 600m | - | at about 16:45 |
| Dec. 7-8 | ??? | - | ??? |
| Dec. 9 | ??? | - | at about 06:16 |
| [2005] | | | |
| Apr. 12 | ??? | - | at about 04:45 |
| May 18 | ??? | - | at about 02:41 |
| [2006] | | | |
| Feb. 17 | ??? | - | at about 22:38 and/or 23:34 |
| Aug. 23 | 500m | - | at about 04:25 |
Type:
M: Major explosion (Plume Height > 1000m)
-: Other explosion
About recent Miyake-jima eruptions (1940, 1962, 1983)
Miyake-jima is one of the most active volcanoes in Japan. There are 14 eruptions in historic time. The last 3 eruptions (1940, 1962, 1983) are well documented.
All the three eruptions began with precursory seismic activity of several hours. The eruptions are typically fissure eruptions at the flank, although some summit eruptions are also known. In both types of eruptions, basaltic magma erupted, and lava flow often damaged the towns on the foot of the volcano.
Special precautions is taken against phreato-magmatic eruptions because of its extensive explosivity. In the 1983 eruption, large phreato-magmatic explosions occurred.
The 1940 eruption
- precursory earthquakes = 3.5 hours
- duration of the eruption = 22.5 hours (flank) + 25 days (summit)
- position of the fissure = NE of the island
The 1962 eruption
- precursory earthquakes = less than 2 hours
- duration of the eruption = 30 hours (flank)
- position of the fissure = NE of the island
The 1983 eruption
- precursory earthquakes = 1 hours & 20 min.
- duration of the eruption = 15 hours (flank)
- position of the fissure = SW of the island
Reference: Aramaki & Hayakawa (1984). Miyazaki (1984)
Tomiya's Home Page
TOMIYA, Akihiko
Geological Survey of Japan, AIST
E-mail: 
http://staff.aist.go.jp/a.tomiya/tomiyae.html
Created: July 3, 2000
(Counting since July 12, 2000)
