 |
| Titel |
Physical model of a fumarolic system inferred from a high-resolution 3-D Resistivity image of Solfatara volcano |
| VerfasserIn |
Marceau Gresse, Jean Vandemeulebrouck, Svetlana Byrdina, Giovanni Chiodini, Antonio Pio Rinaldi, Timothy C. Johnson, Tullio Ricci, Zaccaria Petrillo, Giuseppe Vilardo, Thomas Lebourg, Annarita Mangiacapra |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143634
|
| Publikation (Nr.) |
 EGU/EGU2017-7376.pdf |
|
|
|
|
|
| Zusammenfassung |
| Solfatara crater, located inside the Phlegrean Fields caldera, is showing a significant unrest
activity since 10 years with a increase of ground deformation, degassing and heating.
Electrical Resistivity Imaging was performed between 2012 and 2016 with the purpose
of improving our knowledge of the shallow hydrothermal system. The complete
dataset includes 43,432 D-C measurements inverted using the E4D code. This 3-D
inversion was compared with the mappings of surface temperature, diffuse soil
CO2 flux and self-potential in order to better constrain the interpretation of the
observed resistivity structure in terms of lithological contrasts and hydrothermal
signatures.
For the first time, we highlighted in 3-D the main geological units: Monte Olibano lava dome
and Solfatara crypto-dome appear as two relatively resistive bodies (50-100 Ω.m).
Furthermore, the resistivity model clearly revealed the contrasting geometry of the
hydrothermal circulation in the Solfatara crater. A channel-like conductive structure (7 Ω.m)
represents the condensate that flows from the main fumarolic area down to the
liquid-dominated Fangaia mud pool. This interpretation is consistent with the negative
Self-Potential anomaly and with the surface observations.
We imaged at a metric-resolution the two main fumaroles, Bocca Grande and Bocca
Nuova, that have the following geochemical characteristics. Bocca Grande vent:
162∘C, ∼150 t of CO2 released per day with a mass ratio CO2/H20 = 0.4 and Bocca
Nuova vent: 148∘C, ∼50 t of CO2 released per day with a mass ratio CO2/H20 =
0.45.
The differences between these geochemical characteristics could lead one to believe that they
are fed by two distinct sources at depth. On the contrary, our resistivity model shows that
the two fumarolic vents are directly connected to a common resistive body (30-50
Ω.m) at a depth of 50 meters. This structure likely represents a single gas reservoir
feeding the two fumaroles. Its depth corresponds indeed to a steam source at a
pressure of 6 bar and at a temperature of least 165 ∘C. The geophysical images
combined with the geochemical data allowed us to build up a multiphase fluid flow
model of the Bocca Grande and and Bocca Nuova fumaroles using the TOUGH 2
code. Our results show that the distinct resistivity structure, temperature, and water
content of the both fumaroles are due to the particular geometry of the condensate
flow that intersects and contaminates the Bocca Nuova but not the Bocca Grande
fumarole.
These results indicate the necessity to combine geophysical and geochemical approaches in
order to better apprehend the structure complexity and the dynamics of fumaroles and
hydrothermal systems. |
|
|
|
|
|
|