The plinian fallout associated with Quilotoa's 800 yr BP eruption, Ecuadorian Andes

摘要: Abstract Large volcanic eruptions at dacitic or rhyolitic volcanoes often generate exceptional volumes of fine ash that mantles an area up to a million km 2 . These are characterized by extreme fragmentation the magma and hence extraordinary dispersal categorized as plinian, ultraplinian, phreatoplinian events. Large-volume co-ignimbrites co-plinian ashes produced such eruptions. High indices > 90% attributed violent eruption silicic magma, especially if augmented fuel-coolant reactions when abundant external water interacts with magma. The present study documents case where (≤ 1 mm diameter) fall deposit related plinian phase comprises overwhelming bulk – about 87 wt.% eruptive products. This is another example demonstrating predominance widespread, fine-grained, which follows initial coarser lapilli fall. Historical two other Andean Quizapu, (Chile) Huaynaputina, (Peru), Santa Maria, (Guatemala) Novarupta, (Alaska) similar sequences. Quilotoa's 800 yr BP eruption, in Ecuadorian Andes, powerful small volcano. It crystal-rich, fine-grained layer mantled extrapolated ∼ 810,000 km ≥ 1 mm thickness has volume 18.3 km 3 Stratigraphic petrographic studies, well granulometric density analyses were employed investigate these products, particularly distal deposits. cycle consisted phreatomagmatic triggering, establishment sustained column subsequently partial collapses, leading widespread surge flow activity. (VEI) Volcano Explosivity Index = 6, generated maximum height 35 km mass discharge rate ∼ 2 × 10 8  kg/s. In comparison, Pinatubo's 1991 had heights rates but smaller erupted volumes. Factors possibly contributed explosiveness resulting production include inferred volatile overpressures crystal-dominated dacite rapid onset, forceful column, through crater lake, thus promoting without leaving evidence wet, phreatoplinian-type