Active structures and thermal state of the Piton de la Fournaise summit revealed by combined UAV magnetic and thermal infrared measurements

Lydie Gailler,Edouard Régis,Aline Peltier,Phillipe Labazuy,Valérie Ferrazzini

doi:10.30909/vol.05.01.4154

Abstract

In this study, we demonstrate the strong potential of combining Unmanned Aerial Vehicle (UAV)-based thermal infrared (IR) and magnetic measurements to image the thermal state of volcanic edifices, as well as the distribution of active volcano-tectonic features at depth. Since magnetization is strongly dependent on temperature and alteration, thermally active structures are also associated with a decrease in magnetization. Based on the analysis of recent combined magnetic and infrared acquisitions, we focus on the recent evolution of the summit activity at Piton de la Fournaise. The comparison clearly highlights zones of major thermal activity, alteration and high permeability, and potentially areas of low mechanical resistance. Those observations provide information on preferential pathways for future activity, and also provide constraints on fluid transfer, diffusion, and cooling processes occurring within the volcano subsurface. Through reiterations, such combined UAV measurements are therefore particularly relevant in monitoring volcanic hazards before, during and after eruptions.

Highlights

Magma transfer pathways from the magma plumbing system to the surface are strongly dependent on the inherited structure and the thermal state of the edifice [e.g. Patrick and Witzke 2011; Wessels et al 2013; Antoine et al 2017; Dumont et al 2019; Bouligand et al 2020]
Unmanned Aerial Vehicle (UAV) have only recently come into use for geophysical surveying [Antoine et al 2020; James et al 2020] with, among others, the example of high resolution digital elevation models (DEM) [Derrien 2019], IR mapping [Wessels et al 2013], and magnetic imaging [Catalán et al 2014]
We used a high-sensitivity and high-performance scalar magnetometer, the QuSpin Total-Field Magnetometer (QTFM; Figure 2A), based on an optically pumped rubidium sensor. It is associated with an Electronic Control Unit (ECU), an Advanced Communication Board (ACB) and a GNSS receiver (1 s acquisition rate)

Summary

Introduction

Magma transfer pathways from the magma plumbing system to the surface are strongly dependent on the inherited structure and the thermal state of the edifice [e.g. Patrick and Witzke 2011; Wessels et al 2013; Antoine et al 2017; Dumont et al 2019; Bouligand et al 2020]. Patrick and Witzke 2011; Wessels et al 2013; Antoine et al 2017; Dumont et al 2019; Bouligand et al 2020] Their evolution through time should be as precisely imaged as possible in order to help to image potential preferential pathways for future activity (i.e. weakness zones such as pre-existing fractures, previous intrusive fissures and altered area). Recent studies have shown the potential of magnetic field measurements to image temperature anomalies (due to the strong influence of temperature on magnetization) and mechanical heterogeneities [for example fracturing and alteration; Gailler and Lénat 2012; Gailler and Kauahikaua 2017; Bouligand et al 2019; Dumont et al 2019]. The two parameters can be combined and used to provide constraints on fluid transfer, diffusion, and cooling processes

Objectives

Methods

Findings

Discussion

Conclusion