Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes

Abstract

On March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products, mostly lithic blocks, some of which impacted the ground as far as down to 200 m a.s.l., about 1.5 km far away from the active vents.Two days after the explosion, a new vapour emission was discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called "Nel Cannestra". This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO(2) soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10-15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow, with a temperature close to the water boiling point (76 degrees C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 degrees C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestra, at similar to 500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO(2) soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the N41 degrees regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained on Mount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the northeastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit. (C) 2010 Elsevier B.V. All rights reserved

Diffuse carbon dioxide emissions from hidden subsurface structures at Asama volcano, Japan

“…The low-resistivity structure reported by Aizawa et al (2008) and by Koyama et al (2013) is thought to correspond to both the fluid and the sealed layers. To elucidate the boundary separating the fluid from the sealing layers, accurate surveys must be conducted using very-lowfrequency magnetotelluric techniques (Zlotnicki et al 2006) or direct current resistivity measurements (Revil et al 2008;Finizola et al 2010). Based on the results reported by Aizawa et al (2008), the altitude of the top of the low-resistive body beneath the western part is lower than that beneath the eastern part.…”

“…However, it is difficult to ascertain whether the low-resistive body represents hydrothermal water or altered smectite-rich layers solely by the resistivity observations. Consequently, to delineate hydrothermal fluid within volcanic edifices, diffuse CO 2 flux measurements are often conducted with resistivity observations (e.g., Revil et al 2008;Finizola et al 2010). The diffuse CO 2 survey makes it possible to distinguish a contributing factor of the low-resistive structure because diffuse CO 2 cannot ascend in soil that is sealed by clay minerals having low permeability.…”

Hydrothermal system of Central Tenerife Volcanic Complex, Canary Islands (Spain), inferred from self-potential measurements

“…To investigate electrical resistivity distribution, electrical resistivity tomography (ERT) is of prime importance (see Revil et al, 1999aRevil et al, ,b, 2004Revil et al, , 2010Finizola et al, 2006Finizola et al, , 2010, but it is an arduous and time-consuming method requiring the mobilization of hundreds of kilograms of instrumentation and water, making very difficult to cover wide areas of rough terrain with enough measurement profiles to extract a complete structural image. The self-potential method, on the other hand, is a passive technique (without any artificial electrical sources), relatively quick and simple to perform and requiring transportation of only few kilograms of material.…”

Architecture and temporal variations of a terrestrial CO2 degassing site using electric resistivity tomography and self-potential

“…While many studies have focused on CO 2 capture and storage sites, far fewer studies exist that used geoelectrical methods at natural, terrestrial degassing sites. Most of these CO 2 degassing studies either used geoelectrical methods (Flechsig et al 2008;Nickschick et al 2015;Pettinelli et al 2010;Schütze et al 2012a, b) or combined them with self-potential methods (Revil et al 2008(Revil et al , 2011Byrdina et al 2009;Finizola et al 2010;Sandig et al 2014;Sauer et al 2013). Although all of these studies can reveal the underground structure of degassing sites (Ramirez et al 2003;Bergmann et al 2012Bergmann et al , 2016, the aspect of changes over time within these degassing sites has only been scarcely researched (Drahor et al 2012;Fedele et al 2015).…”