Figure 1: Physical observations of volcanic ash aggregation.
From: Hail formation triggers rapid ash aggregation in volcanic plumes
Observations during the 2009 eruption of Redoubt Volcano in Alaska.(a) Extent of the mapped ashfall deposit19 from event 5 of the eruptive sequence. Scale bar, 50 km. Maximum diameters of ash aggregates indicated by white circles. ‘*’ denotes two closely spaced sites. Yellow triangle shows location of Redoubt Volcano. (b–c) Thin sections of ash aggregates (plane-polarized light), which landed frozen 12 km from Redoubt Volcano. Scale bar, 1 mm. The frozen ash aggregates are commonly (b) unstructured with slight fining outward from the centre (arrows) or (c) contain concentric layers of ash particles. (d) Total grain-size distribution in the volcanic plume before and after aggregate formation. Data are binned into whole-ϕ intervals (where ϕ=−log2D in mm). Vertical bars indicate the eight volcanic tracers used in the ATHAM large-eddy simulation. Lower axis shows diameter in microns, upper axis in ϕ.
