Scale-dependent location of hydrothermal vents: Stress field models and infrared field observations on the Fossa Cone, Vulcano Island, Italy

Abstract

Hydrothermal venting occurs on numerous volcanoes of various age, setting, topographic and structural expression. Vent locations are commonly found not within volcanic craters only, but predominantly at the crater margins and topographic highs. A case example is Vulcano Island, Italy, where the control on such vent locations along crater margins remained poorly understood, however. This paper describes numerical models combined with field observations and infrared imaging to explore the mechanisms that control the ascent paths of fluids in the Fossa cone on Vulcano. Using finite element modelling we calculate the gravitational stress in the volcanic edifice imposed by the topography. Results predict hydrofractures to be arranged in radial patterns at depth and in concentric patterns close to the surface. Furthermore, low compressive stress values are found at the rims of the nested craters. We compare the stress models to fumarole field data: Using a forward looking infrared camera we recorded images of the entire cone. Images were assembled to a mosaic and geocoded, providing the first map of a remotely sensed temperature field in high resolution at La Fossa. The degassing and high temperature anomalies are found to be located mainly at the crests of the craters, predominately in the northern and southern sector of the main crater. Therefore, the stress distribution favours and indeed corresponds to the occurrence of fumaroles at La Fossa. The stress models also yield compression at the bottom of the crater where temperatures are cool. Thus, we consider that the overall distribution of the fumaroles at the Fossa cone is controlled by topography. Additional mechanisms contribute to the exact position of the degassing sites: The influence of the lithological control seems to be strong in the southwestern part of the crater where the fumaroles are located 10-20 m below the inner crater rim in bedded strata. In the northern part of the crater, the exhalation sites can mainly be found at surface fractures and cracks emphasizing the structural control on the location of the fumaroles at this sector of the Fossa cone. Using combined theoretical modelling and field observations, this study helps to shed light into the processes directing fluids in volcanic edifices elsewhere and might contribute to the evaluation of upcoming hazard scenarios.

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

“…4a). As mentioned in the BIntroduction,p athways of the ascending fluids including CO 2 are controlled by topography, lithology, and/or volcano-tectonic structures (Schöpa et al 2011;Peltier et al 2012;Pantaleo and Walter 2014;Hutchison et al 2015). Here, we evaluate possibilities of these factors.…”

“…Recently, Hutchison et al (2015) presented evidence that, at Aluto volcanic complex, Main Ethiopian Rift, the fluid pathways are controlled not only by pre-and post-caldera structures at large scale but also by topography and surface lithology at small scale using soil CO 2 flux measurements and geomorphological analyses. This idea is based on recent thermal infrared imagery studies focusing on the fluid ascent in volcanoes (Schöpa et al 2011;Peltier et al 2012;Pantaleo and Walter 2014). Schöpa et al (2011) showed that, at Vulcano Island, positions of the fumaroles around the crater rims are controlled by topography at the large scale and by lithology and structures at small scale.…”

“…This idea is based on recent thermal infrared imagery studies focusing on the fluid ascent in volcanoes (Schöpa et al 2011;Peltier et al 2012;Pantaleo and Walter 2014). Schöpa et al (2011) showed that, at Vulcano Island, positions of the fumaroles around the crater rims are controlled by topography at the large scale and by lithology and structures at small scale. At the crests of the craters, stress field variations induced by topography encourage fluid ascent (Schöpa et al 2011).…”

“…Schöpa et al (2011) showed that, at Vulcano Island, positions of the fumaroles around the crater rims are controlled by topography at the large scale and by lithology and structures at small scale. At the crests of the craters, stress field variations induced by topography encourage fluid ascent (Schöpa et al 2011). Peltier et al (2012) indicated that, at Yasur-Yankahe volcanic complex, Vanuatu, hydrothermal areas were linked with planar stratification and structures such as faults and old crater rims.…”

Soil CO2 Degassing Path along Volcano-Tectonic Structures in the Pico-Faial-São Jorge Islands (Azores Archipelago, Portugal)

“…In fact, in the last 30 years, CO 2 spatial distribution has been used worldwide to identify hidden tectonic structures, since faults/fractures act as preferential pathways (high permeability zones) for the escape of gases from the deep crust or mantle to the surface (Giammanco et al, 1999(Giammanco et al, , 2006Baubron et al, 2002;Hutchison et al, 2015;Liuzzo et al, 2015). Based on the release of soil gases in confined areas, Chiodini et al (2001) named the anomalous CO 2 degassing areas, where hydrothermal/volcanic CO 2 is released, as diffuse degassing structures (DDS), whose shape depends on morphological, geological, and structural factors, such as the topography, existence of lithological heterogeneities, and presence of faults/fractures (Schöpa et al, 2011;Peltier et al, 2012;Pantaleo and Walter, 2014).…”