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THE PROBLEM !!. NOT THE PROBLEM !!. VOLCANIC ASH. An unconsolidated mixture of sand to dust sized (1mm to .001 mm) rock and mineral fragments produced during explosive eruptions.
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VOLCANIC ASH • An unconsolidated mixture of sand to dust sized (1mm to .001 mm) rock and mineral fragments produced during explosive eruptions. • Rock fragments are typically glassy and form as liquid magma quenches following its eruption at the earth’s surface • Mineral fragments include plagioclase feldspar, hornblende, and pyroxene. These melt at higher temperatures than do the glassy rock fragments. • Ash is hard, sharp, and angular.
Frequency of Ash Cloud Hazard • North Pacific volcanoes average 5-6 eruptions per year, with ash at flight levels on 4-5 days per year. • On an additional 10-12 days per year, ash clouds are estimated to be close enough to flight routes to be a concern to aviation. • Empirical estimates based on a combination of a 20-year record and a 200-year historical record (Miller and Casadevall, 2000) • Extrapolation to the rest of the world shows that ash is expected to be at flight levels on 20-25 days per year, and a concern on 50-60 days per year.
