4:30 PM - 4:45 PM
[SVC41-11] The estimation of the flow regime of gas phase of Strombolian eruptions at Aso volcano
Keywords:Strombolian eruption, Aso Volcano
At Aso volcano in Japan, repetitive Strombolian eruptions occurred during November 2014 – May 2015 and these eruptions were recorded by our observation network equipped around the active crater; a camera, seismometers, and low-frequency microphones. We extracted 702 infrasound events with STA/LTA method as a proxy of Strombolian explosions and confirmed that these all events accompanied VLP and high-frequency seismic signals as well. The source of VLP signals at Aso volcano has been identified as a resonance of a large crack (Yamamoto et al., 1999) which is connecting to the crater via a cylindrical conduit. Assuming that insertion of a slug from the crack to the conduit at ~300 m depth excites the VLP signal and an explosion generates the infrasound signal, we could estimate the ascending velocity of the slug before and after April 2015 as 0-150 m/s and 100-300 m/s. However, according to empirical correlation, maximum bubble rising speed at Aso volcano is only 7.7 m/s. To explain the discrepancy of these velocities, we propose here an alternative flow model of the gas phase in the conduit; a churn-flow model. In the slug flow, the liquid film surrounding the slug falls downward. The slug flow changes to the churn flow as gas flux gets over a threshold in which the gas flux is large enough to bring up and oscillate the liquid film. The critical gas phase velocity is reported as 76 m/s by Urivieli et al. (2013). This velocity is comparable with the order of our estimation velocity at Aso volcano. We should confirm the applicability of the churn-flow model using the other observational results in the further works.