Quantitative scanning-electron microscope analysis of volcanic ash surfaces; application to the 1982-1983 Galunggung eruption (Indonesia)

Qualitative analyses of volcanic ash are time-consuming and subjective, whereas quantitative analyses are methodical and automated. Not only volcanic ash particles, but also many natural particles have been widely described and quantified by their outlines. The qualitative data of volcanic ash surfaces need to be expressed quantitatively, supported by supplementary methods such as statistical analysis and artificial intelligence. Well-defined surface descriptors can be applied to volcanic ash particles. In this study, roughness and texture descriptors of pyroclastic material from the 1982-1983 eruption of Galunggung (Java, Indonesia) were used to describe the vesicle surfaces of the particles, alteration intensity, and/or fine particle abundance. These parameters are important for distinguishing the products of magmatic eruptions from those of phreatomagmatic eruptions. Further application of this method may allow these descriptors to be easily converted to alteration grade, vesicularity index, intensity of the fragmentation mechanism, and relative proportions of the pyroclast types. Hence, discrimination between products of different fragmentation mechanisms may permit forecasting of volcanic hazards.