Abstract
Quiescent volcanoes dissipate a large part of their thermal energy through hot soils and ground degassing mainly in restricted areas called Diffuse Degassing Structures. La Solfatara crater represents the main spot of thermal release for the Campi Flegrei volcano (Italy) despite its reduced dimensions with regards to the whole caldera. The purpose of this study was to develop a method to measure thermal energy release extrapolating it from the ground surface temperature. We used imaging from thermal cameras at short distances (1 m) to obtain a mapping of areas with thermal anomalies and a measure of their temperatures. We built a conceptual model of the energy release from the ground to atmosphere, which well fits the experimental data taken in the La Solfatara crater. Using our model and data, we could estimate the average heat flux in a portion of the crater as q a v g = 220 ± 40 W / m 2 , compatible with other measurements in literature.
Highlights
One of the most obvious signals of activity of a volcano is the fumarolic emission and the associated heat release [1,2]
We emphasize that the thermal energy released by the hot soils of La Solfatara (∼1013 J/d [3]) is much larger than both the heat conductively transmitted over the entire caldera (∼100 km2) and the energy dissipated by earthquakes and ground deformation [3] in the current period of volcanic quiescence
We avoided the use of the thermal camera in windy conditions or sun irradiation, and we selected only measurements performed at night or in the first hours of the day just before sunrise
Summary
One of the most obvious signals of activity of a volcano is the fumarolic emission and the associated heat release [1,2]. The steam is not emitted by the fumaroles but condenses in the subsoil forming hot soils diffusely degassing the incondensable species (mainly CO2). Hot soils and ground degassing does not occur throughout the whole volcanic or hydrothermal areas, but from restricted areas called Diffuse Degassing Structures (DDS), commonly associated with areas of high permeability related to faults or fractures [3,4]. We emphasize that the thermal energy released by the hot soils of La Solfatara (∼1013 J/d [3]) is much larger than both the heat conductively transmitted over the entire caldera (∼100 km2) and the energy dissipated by earthquakes and ground deformation [3] in the current period of volcanic quiescence. Since this method only gives punctual measurements of the thermal gradient, it is a very time consuming methodology when used to estimate the heat release from a large area, because it needs the collection of several samples and it may require weeks to be brought to a conclusion [13,14,47]
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