Sakura-jima and a riddle!

Sakura-jima, one of Japan’s most active volcanoes, is a 13,000 year old Decade volcano located in Kyūshū, Japan, overlooking the city of Kagoshima (population of 680,000 approx).

An ash-rich eruption column rises above Sakura-jima volcano on September 9, 1985 (Tom Pierson – U.S. Geological Survey)

Sakura-jima lies in the Aira Caldera which formed during an eruption 22,000 years ago. This eruption is believed to have been in the order of a VEI7, producing large pyroclastic flows, a caldera 17 × 23 km-wide and large pumice fall. It is estimated that somewhere in the order of 400 km3 of tephra was erupted.

Sakura-jima, itself, is a stratovolcano with three peaks: Kita-dake, Naka-dake and Minami-dake. Kita-dake ( 1,11 m) is the highest peak.

Most of Sakura-jima’s eruptions are Strombolian but it has produced a few Plinian eruptions. Early eruptions were from Kita-dake to 2900BC; activity then moved to the Minami-dake crater, which has been active ever since. After 1914 it had minor explosive activity, including the creation of the Showa crater in 1939. In 1955 activity increased. The volcano may now erupt as frequently as between every four to 24 hours.

Large eruptions occurred in 1471–1476 (VEI 5?), 1779–1782(VEI 4), 1914(VEI 4) and 1946 (VEI 2). Each of these produced andesitic lava flows large enough to alter the coastline of Sakura-jima. The 1914 eruption occurred after a period of dormancy of more than 100 years.

Because of the threat to nearby populations, Sakura-jima was designated a Decade Volcano in 1991, which means that it is monitored as part of the United Nations’ International Decade for Natural Disaster Reduction.

Sakura-jima is heavily monitored: both the Japanese Meteorological Agency (JMA) and Kyoto University’s Sakurajima Volcanological Observatory (SVO) monitors the volcano’s activity. SVO was set up in 1960. Monitoring techniques used at Sakura-jima are:

Ground deformation, including a tide levels in the bay.
Seismometers detect earthquakes which occur immediately beneath the crater, signaling the onset of the eruption. They occur 1 to 1.5 seconds before the explosion.
Tiltmetre systems measure minute movements of the mountain.
Ground water temperature.
Remotes sensing is used on Sakurajima since the gases are highly toxic: the ratio of HCl gas to SO2 gas increases significantly shortly before an eruption.

Kagoshima has an interesting history, including being attributed the birthplace of Japan’s industrial revolution after a group of its students shared Western science and technology gleaned from a clandestine visit to England and the USA. It is also called the “Naples of the Eastern World”, having a similar bay and climate as its namesake in Italy; Kagoshima’s bay is from the Aira Caldera.

Kagoshima conducts regular evacuation drills; it has built shelters where people can take refuge from volcanic ash; and, it also has an extensive system of man-made channels and dams (Sabo dams) to provide protection from lahars. Kagoshima City’s website has useful information on what to do to prepare for an eruption and what to do in the event of an eruption: http://www.city.kagoshima.lg.jp/gaikokugo/english/emergency.html

Sakura-jima’s volcanic activity is fed by lavas created by the subduction of the Pacific Plate under the Eurasian Plate – more about this later.

KarenZ, September 4, 2012

References:

Aramaki, Shigeo (1984). “Formation of the Aira Caldera, Southern Kyushu, ∼22,000 Years Ago”. Journal of Geophysical Research 89 (B10): 8485–8501. Bibcode 1984JGR….89.8485A. doi:10.1029/JB089iB10p08485. http://www.agu.org/pubs/crossref/1984/JB089iB10p08485.shtml.
http://www.photovolcanica.com/VolcanoInfo/Sakurajima/Sakurajima.html
The Smithsonian Institution GVP: http://www.volcano.si.edu/world/volcano.cfm?vnum=0802-08=
Wikipedia: http://en.wikipedia.org/wiki/Sakurajima
Wikipedia: http://en.wikipedia.org/wiki/Kagoshima,_Kagoshima
Wikipedia: http://en.wikipedia.org/wiki/Decade_Volcanoes
Webcams

http://webcam-svo2.pr.kyoto-u.ac.jp/local/camera.html
http://373news.com/_sakucap/index.php?time=1343204842#live_cam

KarenZ

An evil riddle by AlanC

Ruddy cephalopods – when they get angry, they come out in lumps!
What am I?
Where am I found?
How was I formed?

Good hunting!