Tephra stratigraphy of Misti volcano, Peru

Abstract

Misti volcano in Peru has produced many pyroclastic falls and flows over the last 34,000yr. Three groups are distinguished within the pyroclastic stratigraphy. The first group is composed of a few mica-bearing, rhyolitic pyroclastic fall and flow deposits older than 34,000yr BP, which represent the oldest pyroclastic deposits attributed to Misti. The second group consists of several mica-bearing, dacitic fall deposits erupted between 34,000 and 31,200yr BP. The third group is made up of several tens of amphibole- and pyroxene-bearing, andesitic pyroclastic-fall and flow deposits. Most deposits of this latter group were erupted between 31,200 and 24,840yr BP, a few others between 24,840 and 10,670yr BP, and the last at 1920yr BP. Most fallout deposits represent plinian and subplinian eruptions of less than 1km3 (DRE). Mineral assemblages and major-element compositions define a high-K calc-alkaline series, while Sr (>400ppm) and Y (<18ppm) contents are typical of adakitic magmas. The city of Arequipa (700,000 population) is located 17km from, and 3500m lower than, Misti. The four primary volcanic hazards for Arequipa include ash and pumice fallout, pyroclastic flow, lahar, and debris avalanche. Those points emphasise the fact that Misti must be considered a high-risk volcano and deserves more interest than it has received to date.