Fig. 12.

SiO₂ variation diagrams for bulk ash compositions (2008–2011), and bulk rock compositions of Shinmoe-dake ejecta in 2011 eruption (Suzuki et al., 2013) 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. For the 2011 eruption, data for pumice blocks (white, and gray- and brown-colored) are from the three sub-Plinian eruptions and later explosion (January 28), while lava data are from February 1 vulcanian eruption (Suzuki et al., 2013). 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 SiO₂-K₂O diagram show the compositional changes of representative ejecta (2011 lava and white pumice), when up to 20 wt% of their groundmass (63.9 wt% SiO₂ and 2.4 wt% K₂O in lava; 76.6 wt% SiO₂ and 4.5 wt% K₂O in white pumice; Suzuki et al., 2013) is separated from the bulk rock composition. Also see Subsections 5.2 and 6.4. Color version available online.