ON MODELING BUBBLES IN A MAGMATIC CONDUIT

Many volcanoes exhibit long-period (LP) seismic signals, believed to be resonances of the volcanic system itself. While LP signals have been used successfully to detect incipient eruptions, their use for interpreting the interior dynamics has been explored less. We investigate the hypothesis that the primary cause of the LP signals is the motion of the gas bubbles in the magmatic conduit. In order to better understand that, it is necessary to model in detail the evolution of the magmatic gas phase.

We employ boundary-element methods paired with fast-multipole methods to model the dynamics of the bubble flow in the magmatic conduit. We reproduce the detailed 3D evolution of a cluster of bubbles, as well as their growth due to exsolution and decompression during bubble rise. We aim at reproducing the regular degassing events occuring during Strombolian activity and at estimating the effects on resonant signals. We compare our estimates with an online database of seismograms and discuss the implications. This should give greater insight on how the volcanic system functions, and allow for further progress in the interpretation of long-period seismic signals.