Quilotoa's 800 yr BP eruption, in the Ecuadorian Andes, is an example of a powerful plinian eruption at a small dacitic volcano. It produced a crystal-rich, fine-grained ash layer which mantled an extrapolated 810,000 km2 with ≥ 1 mm thickness and has a bulk magma volume of about 18.3 km3. Stratigraphic and petrographic studies, as well as granulometric and density analyses were employed to investigate these eruptive products, particularly the distal co-plinian fall deposits. The eruptive cycle consisted of a phreatomagmatic triggering, the establishment of a powerful sustained plinian column and subsequently partial column collapses, leading to widespread surge and ash flow activity. Quilotoa's 800 yr BP eruption has a (VEI) Volcano Explosivity Index = 6, and generated a maximum column height of about 35 km and a mass discharge rate of 2 × 108 kg/s. In comparison, Pinatubo's 1991 eruption had similar column heights and discharge rates but smaller erupted volumes.
Factors that possibly contributed to the extreme explosiveness and resulting fine-grained ash production include inferred volatile overpressures in the crystal-dominated dacite magma, a rapid eruption onset, a forceful and sustained plinian column, possibly through a crater lake, thus promoting extreme fragmentation of the magma, but without leaving evidence of wet, phreatoplinian-type deposits.