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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #Nouvelle brève

A new scientific publication from the OVPF / IPGP in collaboration with the BRGM, the University of La Réunion and Sorbonne University, on imaging the internal structure of Piton de la Fournaise by high resolution 3D airborne electromagnetic measurements is available at:
https://www.nature.com/articles/s41598-019-54415-4

The ReunEM project made it possible, during the austral winter 2014, to provide complete helicopter coverage of Reunion Island in high resolution magnetism and electromagnetism. © BRGM

After reading the video, here are some excerpts. For the full original text in English, see the source link.

"The global understanding of the volcanic structure and its dynamics is thus limited by the study of the surface, the spatial resolution and the depth of penetration of the ground methods, but also by human and material resources and difficult environments.

Here, we show for the first time that an airborne electromagnetic survey provides a 3D global resistivity model of an active volcano. The high resolution survey acquired at the Piton de la Fournaise volcano on Reunion Island, Indian Ocean, shows unprecedented details of the internal structure of the building, highlighting the hydrothermal upwelling system under the craters, magma intrusion pathways and inherited faults. Associated with surface surveillance, these aerial images have a high potential for better characterizing the internal structure of the volcano and magmatic processes, and therefore for better anticipating catastrophic events such as phreato-magmatic eruptions or destabilization of volcanoes. "

Presentation of the most active part of Piton de la Fournaise: the Enclos Fouqué caldera. (B) Map of La Réunion Island with the two volcanoes: PdN: Piton des Neiges - PdF: Piton de la Fournaise. The study area is delimited by a red dashed square. (C) Digital elevation model with the location of the recent volcano-tectonic seismic activity (colored circles), eruptive fissures visible in the field (in black solid line), the three rift-zones: NE, SE and N120 (Bachèlery, 1981), and the N65 (in green dashed lines) and Plaine des Osmondes (in blue dashed line) faults as defined by Michon and Saint-Ange (2008). Maps B and C have been generated with Illustrator CS6 and the open source QGIS 3.8.3, respectively. Coordinates in meters (WGS84, UTM 40S). - image extracted from doc. referenced in source

Presentation of the most active part of Piton de la Fournaise: the Enclos Fouqué caldera. (B) Map of La Réunion Island with the two volcanoes: PdN: Piton des Neiges - PdF: Piton de la Fournaise. The study area is delimited by a red dashed square. (C) Digital elevation model with the location of the recent volcano-tectonic seismic activity (colored circles), eruptive fissures visible in the field (in black solid line), the three rift-zones: NE, SE and N120 (Bachèlery, 1981), and the N65 (in green dashed lines) and Plaine des Osmondes (in blue dashed line) faults as defined by Michon and Saint-Ange (2008). Maps B and C have been generated with Illustrator CS6 and the open source QGIS 3.8.3, respectively. Coordinates in meters (WGS84, UTM 40S). - image extracted from doc. referenced in source

Location of the 3.655 inverted AEM soundings (blue dots) above the active part of the Piton de la Fournaise volcano (i.e. the Enclos Fouqué caldera), displayed on the magnetic anomaly map (reduced to the pole to lined-up anomalies with magnetic sources). The eruptive fissures visible in the field are denoted in black. The number refers to the negative magnetic anomalies discussed in the text. The 2D profiles (A–D) are marked with white/black lines (the color of the line changes each 500 m). The map has been created using open source QGIS 3.8.3. Coordinates in meters (WGS84, UTM 40S).  - image extracted from doc. referenced in source

Location of the 3.655 inverted AEM soundings (blue dots) above the active part of the Piton de la Fournaise volcano (i.e. the Enclos Fouqué caldera), displayed on the magnetic anomaly map (reduced to the pole to lined-up anomalies with magnetic sources). The eruptive fissures visible in the field are denoted in black. The number refers to the negative magnetic anomalies discussed in the text. The 2D profiles (A–D) are marked with white/black lines (the color of the line changes each 500 m). The map has been created using open source QGIS 3.8.3. Coordinates in meters (WGS84, UTM 40S). - image extracted from doc. referenced in source

{...} "Faced with geological and geophysical results, an AEM survey makes it possible to define:

- the 3D geometry of the shallow hydrothermal system rising under the craters,

- the location and vertical pathways of the dense magma intrusion system along the three rift zones, and

- the extension of deep volcano-tectonic structures from surface lineaments to deep seismic activity under the mobile and unstable flank of the east.

The airborne data set improves our understanding of the geological history of Piton de la Fournaise and its possible future evolution by imagining the zones of weakness resulting from different volcanic processes and by supporting and validating the previous hypotheses. Its ability to detect the three main characteristics of destabilization over a large area, as well as geological observations and / or geophysical measurements, provides essential information to understand their interconnection. We present a reliable geometry of the hydrothermal system, emphasizing its presence near the summit and its possible role in the continuous movement of the eastern flank. We define six main routes of magma injection into the rift zone, improving our understanding of near-surface magma routes and eruptive dynamism. Finally, we also demonstrate that the topographic scars of previous destructive events correspond to deep fault planes where the volcanic deformation accumulates mechanical stresses which can be reactivated during future volcanic destabilization.

In the future, the Piton de la Fournaise monitoring program will integrate the areas of weakness identified in this study to improve the monitoring effectiveness of volcanoes. The integration of the airborne results into a realistic and detailed 3D model of the building will also help to interpret the dynamism and instabilities of the volcano.

 

Sources: Dumont, M., Peltier, A., Roblin, E. et al. Imagery of internal structure and destabilization features of active volcano by 3D high resolution airborne electromagnetism. Sci Rep 9, 18280 (2019) doi: 10.1038 / s41598-019-54415-4

https://doi.org/10.1038/s41598-019-54415-4

Piton de La Fournaise - Dolomieu - 3D extraction of the conductive body from the AEM resistivity model. The model is shown as a function of the elevation of each cells overlayed with the magnetic RTP map. - image extracted from doc. referenced in source

Piton de La Fournaise - Dolomieu - 3D extraction of the conductive body from the AEM resistivity model. The model is shown as a function of the elevation of each cells overlayed with the magnetic RTP map. - image extracted from doc. referenced in source

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