Publication Date:
2021-03-16
Description:
Understanding gas-magma dynamics in volcanic conduits and linking them with the associated geophysical
signals at the surface is of fundamental importance in monitoring active volcanoes. In the past, a significant
number of studies have been devoted to this topic, addressing the onset, the key factors governing each degassing
regime and the related markers at the surface, particularly at basaltic volcanoes. Here, we first review
such a broad and increasing literature, focusing on the main approaches used in the attempt of deciphering
conduit dynamics by indirect observations: 1) analogue laboratory experiments; and 2) seismo-acoustic measurements.
Then, we combine the two techniques into a novel set of experiments, addressing a crucial, yet
unexplored, issue: the irregularity (i.e. the departure from an ideal smooth cylindrical shape) of the conduit
surface. We built a set of epoxy conduits with various fractal dimensions (Dc; i.e. irregularity) of the internal
surface, using silicone oil as a proxy for magma. Different degassing patterns (bubbly, slug and churn-annular
flow) were reproduced by changing systematically: 1) injected gas flux (5 to 180×10−3 l/s); 2) analogue
magma viscosity (10 to 1000 Pas); 3) fractal dimension (Dc) of the conduit surface (i.e. Dc=2, Dc=2.18 and
Dc=2.99). The experiments were monitored by means of a video-camera and a set of sensor aimed to detect the
seismic and acoustic signals. Results show that viscosity strongly influences the transition among degassing
patterns and the recurrence rate of slug bursts at the surface. Moreover, we observed an increase of the exponent
of the power law equation linking squared seismic amplitude to gas flow rate with conduit roughness; the
opposite trend was noticed with increasing liquid viscosity. These results have important implications for linking
seismic tremor to eruption source parameters such as the volume discharge rate at different volcanoes or for
investigating its temporal evolution at a single vent.
Description:
Published
Description:
317-336
Description:
2V. Struttura e sistema di alimentazione dei vulcani
Description:
JCR Journal
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
