Spectral and Informational Analysis of Temperature and Chemical Composition of Solfatara Fumaroles (Campi Flegrei, Italy).

Simona Tripaldi,Michele Lovallo,Luciano Telesca

doi:10.3390/e23050593

Abstract

Temperature and composition at fumaroles are controlled by several volcanic and exogenous processes that operate on various time-space scales. Here, we analyze fluctuations of temperature and chemical composition recorded at fumarolic vents in Solfatara (Campi Flegrei caldera, Italy) from December 1997 to December 2015, in order to better understand source(s) and driving processes. Applying the singular spectral analysis, we found that the trends explain the great part of the variance of the geochemical series but not of the temperature series. On the other hand, a common source, also shared by other geo-indicators (ground deformation, seismicity, hydrogeological and meteorological data), seems to be linked with the oscillatory structure of the investigated signals. The informational characteristics of temperature and geochemical compositions, analyzed by using the Fisher–Shannon method, appear to be a sort of fingerprint of the different periodic structure. In fact, the oscillatory components were characterized by a wide range of significant periodicities nearly equally powerful that show a higher degree of entropy, indicating that changes are influenced by overlapped processes occurring at different scales with a rather similar intensity. The present study represents an advancement in the understanding of the dominant driving mechanisms of volcanic signals at fumaroles that might be also valid for other volcanic areas.

Highlights

Changes in temperature and composition at fumaroles are widely used to monitor volcanic activity aimed to surveillance [1,2,3]
Radon monitoring series at the two sites of Campi Flegrei caldera (Italy) were analyzed, and the results were compared with the CO/CO2 ratio, CO2 concentration, fumarolic tremor, ground deformation and the cumulative number of days with earthquakes [11,12]; the well correlated time variation of the independent signals suggest a general intensification of volcanic crisis at the caldera and that the current unrest involves an area much larger than the one characterized by seismicity and intense hydrothermal activity
This preliminary analysis shows that for most of the time series the spectral content is mainly concentrated in the region of the very low frequencies that suggests the dominance of the trend

Summary

Introduction

Changes in temperature and composition at fumaroles are widely used to monitor volcanic activity aimed to surveillance [1,2,3]. The time variation in the fumarolic compositions at the Kusatsu-Shirane volcano (Japan) suggest a close relation between activation of seismicity and the increase of magmatic components; the compositional difference among the fumarolic gas recorded at different sites have been interpreted as reflecting the existence of three hydrothermal reservoir and formed by distinct condensation mechanisms [10]. Radon monitoring series at the two sites of Campi Flegrei caldera (Italy) were analyzed, and the results were compared with the CO/CO2 ratio, CO2 concentration, fumarolic tremor, ground deformation and the cumulative number of days with earthquakes [11,12]; the well correlated time variation of the independent signals suggest a general intensification of volcanic crisis at the caldera and that the current unrest involves an area much larger than the one characterized by seismicity and intense hydrothermal activity

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Conclusion