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Earth of fire

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

Publié le par Bernard Duyck
Publié dans : #Actualités volcaniques

Having been responsible for the destruction of Mayan civilization centers within 100 km. during the 5th century (450 +/- 30 years in GVP) in Salvador, Ilopango volcano did again talk to him.

The caldera of Ilopango and Lake - above photo / NASA - below photo / combination of bands 2, 3 and 4 in a Landsat satellite image (1986). geo.mtu.edu
The caldera of Ilopango and Lake - above photo / NASA - below photo / combination of bands 2, 3 and 4 in a Landsat satellite image (1986). geo.mtu.edu

The caldera of Ilopango and Lake - above photo / NASA - below photo / combination of bands 2, 3 and 4 in a Landsat satellite image (1986). geo.mtu.edu

Researchers from Bristol University / UK have discovered that the current tectonic stress field promotes the accumulation of magma and hydrothermal fluids shallow, less than 6 km, in the caldera of Ilopango. The magma contains a significant amount of gas, which indicates that the system is powered for the next eruption.

The Jocotán fault is the southernmost plate boundary fault between the North American and Caribbean plates, and is the northern boundary of along-arc transtensional deformation. ESFZ :El Salvador Fault Zone; G : Guatemala graben; IP : Ipala graben. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Commun.

The Jocotán fault is the southernmost plate boundary fault between the North American and Caribbean plates, and is the northern boundary of along-arc transtensional deformation. ESFZ :El Salvador Fault Zone; G : Guatemala graben; IP : Ipala graben. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Commun.

3D view of the negative density anomaly beneath the Ilopango caldera. a. Oblique view, b. plan view, c. facing north, d. facing west. The low extends to around 6,000 m below sea level and consists of a bifurcated structure with limbs branching toward the shallow subsurface. Latitude and longitude values are in UTM. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Commun.

3D view of the negative density anomaly beneath the Ilopango caldera. a. Oblique view, b. plan view, c. facing north, d. facing west. The low extends to around 6,000 m below sea level and consists of a bifurcated structure with limbs branching toward the shallow subsurface. Latitude and longitude values are in UTM. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Commun.

The caldera of Ilopango, 8km of 11, is located east of the capital-city of San Salvador and occupied by one of the largest lake in the country, contained in the high ramparts of 150 to 500 meters.

The final collapse of the caldera is the result of an eruption of VEI 6, producing the pyroclastic deposits "TBJ / Tierra Blanca Joven" about 1,500 years ago. The only historical eruption of Ilopango date from 1879-1880 and left a largely submerged lava dome in the center of the lake, forming the Quemadas islands.

Map of Bouguer the caldera of Ilopango - The domes are mentioned; the contours of the lake are in full line; those of the caldera dotted line, the asterisk marks the location of the co-ignimbritic lag breccia. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Common.

Map of Bouguer the caldera of Ilopango - The domes are mentioned; the contours of the lake are in full line; those of the caldera dotted line, the asterisk marks the location of the co-ignimbritic lag breccia. - Doc. In Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Common.

Engraving of the 1880 eruption of Ilopango with the birth of Quemadas islands. - Infrogmation

Engraving of the 1880 eruption of Ilopango with the birth of Quemadas islands. - Infrogmation

Ilopango - ash and pyroclastic flows deposits of the TBJ / Tierra Blanca Joven - Photo Giuseppina Kysar 1999 (Smithsonian Institution)

Ilopango - ash and pyroclastic flows deposits of the TBJ / Tierra Blanca Joven - Photo Giuseppina Kysar 1999 (Smithsonian Institution)

The caldera is controlled by regional faults of the Salvadoran central graben.

According to Dr. Gottsman, project leader and co-author of the study, " localized extension along the rift zone of El Salvador / ESFZ control the accumulation, the ascent and eruption of magma in Ilopango. This magma accumulation controlled by faults, and his movements, limit the potential location of future eruptions vents in the central, western and north of the caldera, an area that is part of metropolitan San Salvador, with a significant risk to a population of two million people. {...} link between areas of tectonic faults and volcanism is however not yet fully understood. "

As often, this kind of study raises many other questions ... How regional tectonic stress accumulation influences the magma buildup between major eruptions formative of caldera ? The answer is important for the understanding of the factors controlling the development of magmatic systems, and the prediction of likely locations of volcanic activity caldera forming in the future.

 

Lake Ilopango and Volcano Chinchontepec - in the foreground, the capital of Salvador - photo Mauro Arias

Lake Ilopango and Volcano Chinchontepec - in the foreground, the capital of Salvador - photo Mauro Arias

Sources:

- Magma build-up May could Salvadoran capital at risk -
link
- Saxby, J. et al. Magma storage in a strike-slip caldera. Nat. Commun.7: 12295 doi: 10.1038 / ncomms12295 (2016) .- link
- Global Volcanism Program - Ilopango - link

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