Event Name : Aniakchak Half Cone Lower Pumice
|Start: 840 (± 40 Years) || Years BP C-14 (raw) || |
|Pyroclastic flow, surge, or nuee ardente: ||
|Eruption Product: || dacite ||
From Bacon and others (2014): "Pumice-fall and pyroclastic-flow deposits from Half Cone are exposed in the north wall of the 1931 Main Crater 2 km to the south (fig. 13D [in original text]). Here, the cliff at the base of the section (fig. 13E [in original text]) is composed of >22 m of partly welded or indurated coarse pyroclastic-flow material, much like spatter-rich pyroclastic-flow deposits at Santorini (Mellors and Sparks, 1991), containing andesite bombs as large as 0.6 m × 2 m and similar in composition to Half Cone pyroclasts (59 weight percent SiO2). This unit is overlain by 13 m of pumiceous cross-bedded surge layers, 31 m of pumice-fall deposits, 5 m of Half Cone ca. 400 yr B.P. spatter agglutinate, and an 81-m-thick section of 1931 materials (Nicholson and others, 2011, their figure 3F). Dacite tephra older than the Pink Pumice and considered to have a Half Cone source, and which therefore may be correlative with proximal deposits at Half Cone and with the section exposed in the 1931 Main Crater, have weighted mean radiocarbon ages of 840+/-40 and 570+/-40 yr B.P. (tables 1 and 2 [in original text], lower and upper light pumice, respectively)."