Gas flux cyclic regime at an open vent magmatic column inferred from seismic and acoustic records

Gen Kondo,Giorgio Lacanna,Ryohei Kawaguchi,Taishi Yamada,Takahiro Miwa,Riccardo Genco,Eisuke Fujita,Hiroshi Aoyama,Maurizio Ripepe,Takeshi Nishimura

doi:10.1038/s41598-019-42033-z

Abstract

On August 7, 2014, a new effusive vent opened on the northern flank of Stromboli. A characteristic pattern was observed in both seismic and infrasonic signal amplitudes prior to this effusive eruption. The pattern consisted of the repeating cycle: (1) quiet phase, (2) puffing phase, and (3) explosion phase. Correlation between seismic and infrasound signal suggests that pulses in the puffing phase were caused by repetitive bursts of small gas pockets at the central crater, while the explosion phase coincided with an explosion at the central crater. We show that degassing of the magma column occurred in cycles of increasing gas flux, which controlled the transition from a bubbly flow (puffing phase), to a slug flow (explosion phase) gas regime. The quiet phase was characterized by a constant time length of 150 s, indicating that the gas rose in the magma column as well-organized waves of gas layers. These cycles represent cyclic changes of the gas flux regime in the shallow magma column, associated with increases in the magma-gas supply input rate before the effusive eruption.

Highlights

Stromboli Volcano, located in the South Tyrrhenian Sea, Italy, is well known for the repetitive emission of volcanic gases with basaltic magma from its summit vents (Fig. 1a)
Explosions and puffing show significant short-term variability, indicating that the degassing activity of the magma column at Stromboli can be very sensitive to changes in the magma supply rate of the shallow feeding system[1,25]
Puffing would be www.nature.com/scientificreports expected to generate small pulses only in infrasonic records, but not in seismic records, which more commonly exhibit a continuous signal typically defined as a tremor[6,18,19], because small seismic transients radiated by puffing repeating with short time interval (

Summary

Introduction

Stromboli Volcano, located in the South Tyrrhenian Sea, Italy, is well known for the repetitive emission of volcanic gases with basaltic magma from its summit vents (Fig. 1a). Explosive activities at Stromboli are classified into three types according to frequency and intensity: normal explosions ( referred to as “explosions”), major explosions, and paroxysms[7] In addition to these activities, moderate and discrete gas emissions are observed in active vents, a process referred to as puffing[6,8]. At 5:15 UTC (hereafter, time is given in UTC), a new flank vent opened at 650 m above sea level on the SDF, and lava effusion started[11] (Fig. 1b) This effusive activity continued until November 13, 2014, with the total volume of lava ejected estimated to be 7.4 × 106 m3 (refs[10,12]). We present a schematic model based on the features of our geophysical data and previous studies on Strombolian activity

Methods

Results

Conclusion