Sakura-jima – What type of lavas does she produce?

A quick re-cap: Sakura-jima is a post-caldera cone of the Aira caldera. She emerged roughly 13,000 years ago on the southern rim of the caldera, building an island which was eventually connected to the Osumi Peninsula during the eruption of 1914. She is located near the junction of several tectonic plates, whose movement drives eruptive activity.
Sakurajima’s lavas have tended to be andesite – dacite. But she has produced effusive lava flows.

Lava rocks along Nagisa Lava Trail on Sakurajima, Jakub Hałun, 2012, Wiki Commons.

In 1914, lava’s filled the strait between the island and the mainland. The 1914 eruption started as explosive with an eruption column and pyroclastic flow. Effusive lavas were produced later after a large earthquake. During the later stages of the eruption the centre of the Aira Caldera sank which seems to indicate that lava is sourced from a common reservoir. Other effusive eruptions occurred in 1471 (believed to be her largest recent eruption), 1779 and 1946.

Kagoshima covered in ash. NYPL Picture Collection — Illustrated London News, 1914, Wiki Commons

A study by Goto, H Ishibashi, T Yanagi looked at the temperatures of her dacite lavas. The temperatures appear to be a consistent (850°C) with few magmatic inclusions in the lavas. The lavas contain phenocrysts of plagioclase, clinopyroxene, orthopyroxene and magnetite. These show a bimodal distribution of plagioclase phenocryst compositions. This implies a) injection of basalt magma into the resident magma chamber; and, b) the magmas are well mixed before eruption.

Yanagi et al (1991) had found that the lava flows became more mafic with time from an initial dacite composition. They proposed a two chamber system with a plagioclase pyroxene plug separating an upper dacite chamber from a lower basalt chamber.

Nagel et al researched this further looking at 12,000 years of eruptive history. They discovered that there was a cycle of mafic and more felsic lavas prior to the 1471 eruption. After the 1471 eruption the mafic content of lava has increased to 55% of the dacite lava showing magma mixing. They propose a shallow dacite magma chamber which is repeatedly flushed with mafic magma from a deeper chamber.

Since 1914 Sakura-jima has been relatively quiet; eruptive activity has been mainly ash, lava bombs and gasses, which may or may not be accompanied by earthquake activity.

KarenZ

References
http://en.wikipedia.org/wiki/Sakurajima
http://www.volcano.si.edu/world/volcano.cfm?vnum=0802-08=
“Petrochemical evidence for coupled magma chambers beneath the Sakurajima volcano, Kyushu, Japan” T Yanagi, Y Ichimaru, S Hirahara – Geochemical Journal, 1991 – terrapub.co.jp
“Apparent temperatures estimated from pyroxene phenocrysts in dacites from Unzen, Kuju and Sakurajima”, S Goto, H Ishibashi, T Yanagi – jpgu.org
“Temporal Geochemical Variations in Lavas From Sakurajima Volcano, Japan”, Nagle, A. N.; Harpp, K. S.; Geist, D. J. http://adsabs.harvard.edu/abs/2005AGUFM.V53B1566N