Explosive Dome Eruptions Modulated By Periodic Gas-Driven Inflation

Tuesday, 16 December 2014
Jeffrey Bruce Johnson, Boise State University, Boise, ID, United States, John J Lyons, Alaska Volcano Observatory Anchorage, Anchorage, AK, United States, Benjamin James Andrews, Smithsonian Institution, Washington, DC, United States, Jonathan M Lees, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States and Benjamin R Phillips, SRA International, Inc. and Geothermal Technologies Office, U.S. Department of Energy, Washington, DC 20585, Washington, DC, United States
Volcan Santiaguito (Guatemala) ‘breathes’ with extraordinary regularity as the edifice’s conduit system accumulates free gas, which periodically vents to the atmosphere. Periodic pressurization controls explosion timing, which nearly always occurs at peak inflation, as detected with tiltmeters. Tilt cycles in January 2012 reveal regular 26 +/-6 min inflation/deflation cycles corresponding to at least ~101 kg/s of gas fluxing the system. Very long period (VLP) earthquakes presage explosions and occur during cycles when inflation rates are most rapid. VLPs locate ~300 m below the vent and indicate mobilization of volatiles, which ascend at ~50 m/s. Rapid gas ascent feeds pyroclast-laden eruptions lasting several minutes and rising to ~1 km. VLPs are not observed during less rapid inflation episodes; instead, gas vents passively through the conduit producing no infrasound and no explosion. These observations intimate that steady gas exsolution and accumulation in shallow reservoirs may drive inflation cycles at open-vent silicic volcanoes.