Magma storage in a strike-slip caldera.

Area of Science:

• Volcanology
• Geophysics
• Tectonics

Background:

• Silicic calderas form from explosive volcanic eruptions triggered by magma withdrawal and collapse along faults.
• The interplay between magmatism and tectonism in caldera systems remains poorly understood.
• Regional stress fields are hypothesized to influence magma reservoir location and fault development.

Purpose of the Study:

• To investigate strike-slip volcano-tectonic relationships.
• To gain insight into the subsurface structure of Ilopango caldera.
• To understand the influence of regional tectonics on caldera evolution and eruption potential.

Main Methods:

• Analysis of Bouguer gravity data from Ilopango caldera, El Salvador.
• Inversion of gravity data to determine the depth and nature of subsurface density anomalies.
• Correlation of gravity anomalies with regional stress orientations of the El Salvador Fault Zone.

Main Results:

• A significant low-gravity anomaly was observed beneath Ilopango caldera, aligned with regional stress orientations.
• Data inversion indicates a low-density structure extending to approximately 6 km depth.
• This structure is interpreted as a shallow volcanic plumbing system, including a hydrothermal and a magmatic reservoir with exsolved vapor.

Conclusions:

• Regional stress patterns, specifically the El Salvador Fault Zone, control magma localization within Ilopango caldera.
• The identified shallow magmatic and hydrothermal system is critical for understanding the caldera's history of explosive eruptions.
• Understanding fault-controlled magma accumulation is essential for assessing future volcanic vent locations and associated hazards.