Analysis of Volcanic Thermohaline Fluctuations of Tagoro Submarine Volcano (El Hierro Island, Canary Islands, Spain)

Anna Olivé Abelló,Evangelos Bakalis,Eugenio Fraile-Nuez,Francesco Zerbetto,Beatriz Vinha,Francisco Machín

doi:10.3390/geosciences11090374

Abstract

Temperature and conductivity fluctuations caused by the hydrothermal emissions released during the degasification stage of the Tagoro submarine volcano (Canary Islands, Spain) have been analysed as a robust proxy for characterising and forecasting the activity of the system. A total of 21 conductivity-temperature-depth time series were gathered on a regular high-resolution grid over the main crater of Tagoro volcano. Temperature and conductivity time series, as manifestations of stochastic events, were investigated in terms of variance and analysed by the Generalised Moments Method (GMM). GMM provides the statistical moments, the structure functions of a process whose shape is an indicator of the underlying stochastic mechanisms and the state of activity of the submarine volcano. Our findings confirm an active hydrothermal process in the submarine volcano with a sub-normal behaviour resulting from anti-persistent fluctuations in time. Its hydrothermal emissions are classified as multifractal processes whose structure functions present a crossover between two time scales. In the shorter time scale, findings point to the multiplicative action of two random processes, hydrothermal vents, which carries those fluctuations driving the circulation over the crater, and the overlying aquatic environment. Given that both temperature and conductivity fluctuations are nonstationary, Tagoro submarine volcano can be characterised as an open system exchanging energy to its surroundings.

Highlights

Hydrothermal vents, found in submarine volcanic islands, release important emissions of hot fluids that rise in a buoyant turbulent plume over the source [1]
Implementing a high-resolution grid of temporal series around and over the main crater reveals temperature and conductivity fluctuations in the whole domain, suggesting that the fields are disturbed by emissions from the volcano and may be far from a thermodynamic equilibrium
The findings show that for both short and long time scales as defined above, the volvolcano area operates as an open system releasing a continuous flux of energy into the cano area operates as an open system releasing a continuous flux of energy into the seaseawater, establishing temperature and conductivity to be non-conservative mean water, establishing temperature conductivity to be non-conservative mean fields fields as a result of local swirls and/orand vortexes

Summary

Introduction

Hydrothermal vents, found in submarine volcanic islands, release important emissions of hot fluids that rise in a buoyant turbulent plume over the source [1]. The fluids mix with the surrounding seawater and rise to a level where their density matches the water outside the plume being able to alter the temperature and salinity fields specific to the vertical seawater structure [3]. These vertical motions generate a horizontal flow, resulting in an anticyclonic vortex of sufficient magnitude to trap water, minerals, tracers, and organisms in a local recirculation [4]. Decoding fluctuations with stochastic analysis tools can shed light and benefit understanding the complexity of hydrothermal emissions [6,7,8]

Methods

Results

Discussion

Conclusion