Geologic Background:
The 8 x 5 km island of Suwanose-jima in the
northern Ryukyu Islands is occupied by a stratovolcano
with two historically active summit craters. In 1884 a
new cone (On-take) with a 450-m-wide crater was formed at
the head of the large breached crater extending to the
sea on the east flank. Intermittent Strombolian eruptions
have occurred since 1949. The volcano has been active
almost continuously since 1956.
Historic Activity:
- Eruptions in 1813, 1877, 1884-1885, 1889, 1914, 1915,
1922, 1925, 1934, 1938, and 1940.
- The largest historical eruption occurred in 1813-14;
as a result, thick scoria beds covered the residential
area and lava flows descended WSW from a new
300-m-diameter crater.
- Large eruptions also occurred in 1884-85 and a lava
flow reached the E coast. The island was evacuated for
about 70 years, but as of 1996 there were around 50
residents.
- In 1949 explosive eruptions began in the central
crater. Occasional strombolian activity has continued to
present.
Recent Activity:
- Eruptions occurred in July and August 1988 with a
3000 meter ash cloud. Explosions and ash clouds from Jan.
to July 1989. Eruptive activity was weak in the first
half of 1990, but explosions became frequent in late
July, and activity was most vigorous in October and
November. Exposions occurred from summit cone in late
October 1991. Frequent explosions and ashfalls were
reported from early to mid May 1992. Increased activity
occurred during late Oct. and early Nov. 1992. Additional
activity occurred Nov. 19-22 with incandescent lava
fountains being observed on night of Nov. 21. Sporadic,
weak ash eruptions during March and April 1993. Weak ash
eruptions in late May. Eruptive activity in mid-August
caused ashfall on the island and other islands 100 km
northeast.
- Weak ash eruptions were observed and explosion sounds
were heard by local residents throughout 1994. Heavy ash
sometimes fell in a village on the island. Ash ejections
were observed in Feb. through May, July through October,
and in Dec.
- Eruptive activity took place from March to Jue and
from August to December 1995. Nine explosions throughout
1995.
- Small eruptions during Jan. 10-13, 1996. Ash eruption
on Feb. 23. Weak ash eruptions on March 5 and 6 and April
14 resulted in small ash falls. Strong eruptions in June
produced volcanic ash clouds. Weak ash eruptions in July.
Weak ash emission in late December.
- An ash column 500-600 m high above the summit
resulted in ashfall. Ash emissions on April 16-17, 1997
sent a column 500-700 m high.
- Elevated activity in Dec. 2000 resulted in two new
craters.
- Several eruptions between May and July 2001.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 9, No. 3 to V. 14,
No. 7)
- Global Volcanism Network (V. 15, No. 12 to V. 26, No.
7).
|