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Explosive eruption column dynamics for crystal-rich magmas

Greg A. Valentine1 , Shanaka L. de Silva2

  • Affiliations: 1Department of Geology, University at Buffalo, Buffalo NY, USA; 2College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis OR, USA

  • Presentation type: Talk

  • Presentation time: Monday 14:30 - 14:45, Room S150

  • Programme No: 3.6.2

  • Theme 3 > Session 6

Abstract

Many deposits of large-volume, caldera-forming explosive eruptions involved magma with high crystal contents (~25-50 vol.%).  Numerical modeling shows that such abundances of coarse crystals in an erupting mixture significantly influence eruption column and pyroclastic current dynamics compared to eruptions dominated by fine ash. In high gas content eruptions that would otherwise produce buoyant plumes/columns, abundant crystals can cause chaotic fountains (collapsing columns). Eruptions with intermediate gas content and abundant crystals can generate fountains and pyroclastic currents under conditions that would produce a buoyant plume in fine ash-only eruptions. Some conditions produce mixed behaviors involving low-altitude fallout of crystals while a buoyant fine-ash plume rises above. Crystal-rich eruptions, particularly large ones, require a new conceptual model where such eruptions can proceed directly to fountaining and ignimbrite deposition without the canonical buoyant eruption plume and basal fall unit.