Tephrostratigraphy and eruptive history of Shinmoedake volcano of the Kirishima volcanoes, Kyushu, Japan

Precursory activity and evolution of the 2011 eruption of Shinmoe-dake in Kirishima volcano—insights from ash samples

“…Miyamoto (2012) also showed that gray pumice blocks are dominant relative to yellow (originally white) pumice blocks, as in the 2011 eruption. For the 1716-1717 lava and older ejecta, Tajima et al (2013) showed that the majority has SiO 2 = 59-63, as plotted in Fig. 12.…”

“…Imura and Kobayashi (1991) and Tajima et al (2013) showed that Setao pumice and Maeyama pumice, both erupted in the earliest phase of Shinmoe-dake activity (10.4 cal ka BP and 5.6 cal ka BP, respectively; Okuno, 2002), contain only two pyroxenes. Tajima et al (2013) showed, for later-stage tephras excluding Kyoho Pumice (1716-1717), that mafic phenocryst assemblages change in a similar manner to those in lavas of similar age.…”

“…Data for past ejecta excluding the 1716-1717 pumice include the Maeyama pumice (5.6 cal ka BP; Okuno, 2002) and lavas erupted in and prior to 1716-1717 eruption. For the 1716-1717 eruption, there is uncertainty about the timing of lava emplacement that took place after the explosive phases (Tajima et al, 2013). The lines with numbers (0, 10, 20) in the SiO 2 -K 2 O diagram show the compositional changes of representative ejecta (2011 lava and white pumice), when up to 20 wt% of their groundmass (63.9 wt% SiO 2 and 2.4 wt% K 2 O in lava; 76.6 wt% SiO 2 and 4.5 wt% K 2 O in white pumice; Suzuki et al, 2013) is separated from the bulk rock composition.…”

“…Recently, Tajima et al (2013) reconsidered the whole eruptive history of Shinmoe-dake, based on 1) the stratigraphy in the craterwall before the 2011 eruption, 2) re-categorization of both lava and tephra in other areas, and 3) new age determinations. Mafic phenocryst assemblages of lavas changed with time, from two pyroxenes in older lava flows to two pyroxenes + olivine in younger lava flows.…”

“…14). (2008)(2009)(2010)(2011), and bulk rock compositions of Shinmoe-dake ejecta in 2011 eruption and past eruptions (Tajima et al, 2013;blue plots). Compositions of ash erupted in early phase of 2010-2011 activity are enclosed by black ovals.…”