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One of Earth's largest known eruptions, the Toba eruption of 75 ka, erupted a minimum of 2800 km 3 of magma, of which at least 800 km 3 was deposited as ash fall. This ash may be entirely of coignimbrite origin and dispersed widely because of high drag coefficients on the predominantly bubble-wall shards. Shards of this shape are broken from the walls of spherical vesicles, which formed in high abundance in isotropic strain shadows near phenocrysts in this crystal-rich magma. © 1987 Geological Society of America.
Rose et al. (1987) studied this question.