Fig. 7.

Typical variation of “lava” particles in early phase of vulcanian stage (February to mid-April). 250–500 μm fraction of February 18, 2011 ash (Table 1). All are photographs taken under binocular microscope at the same magnification. For definition of “lava” particles and its sub-types (“fresh” and “partly-altered”), see Subsection 5.1.1. (a)–(c) are “fresh lava” (corresponding to either lava accumulated in the crater during the 2011 eruptive activity (Section 2) or vesicle-poor part of erupted magma), while (d) is “partly altered lava”. Note the different appearance between “fresh lava” and “partly altered lava”; “fresh lava” particles are more angular and have luster on particle surface. Oxidized particles are identified in (c). “Fresh lava” particles commonly include olivine phenocrysts (Subsection 5.1.1), and one example is seen in (a) (red arrow). Color version available online.