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Open and almost shut case for explosive eruptions: Vent processes determined by SO₂ emission rates at Karymsky volcano, Kamchatka

¹ Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-1116, USA
² Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA
³ Department of Earth and Environmental Science, New Mexico Tech, Socorro, New Mexico 87801, USA

Vent processes were examined at Karymsky volcano, Kamchatka, by measuring SO₂ emissions using a correlation spectrometer (COSPEC). Continuous high-sensitivity COSPEC measurements and physical observations were collected on 11 and 12 September 1999, when Karymsky was producing small ashy eruptions every 5–20 min. Each eruptive event began with an explosion and audible rumbling (lasting 30 s) followed in some cases by audible chugging (lasting to 2 min). Gas plumes accompanied each event, and almost without exception the plumes dissipated and became invisible despite significant SO₂ emissions. Variations in SO₂ output show distinctive patterns that correlate with eruption activity. Maximum SO₂ output occurred following each explosion and then declined rapidly to low, but detectable levels. In contrast, a second type of event, often associated with audible chugging, was characterized by high SO₂ output long after the initial ash blast. Variations in degassing at Karymsky can be explained by secondary boiling, gas-pressure accumulation, and vent resealing. We developed a new application of the COSPEC technique to study the dynamic vent processes of erupting volcanoes. This application provides insights into the processes that occur at the otherwise inaccessible vents of erupting volcanoes particularly when a volcano changes from passive degassing and small explosions to degassing patterns that may precede a larger and more dangerous eruption.

Key Words: SO₂ flux • volcanology • second boiling • vent sealing • eruptions