A sharp volatile-rich cap to the Yellowstone magmatic system

Area of Science:

• Geophysics
• Volcanology
• Seismology

Background:

• Volcanic system stability depends on magma storage depth and volatile exsolution.
• Yellowstone caldera has an upper crustal magma reservoir, but its depth and properties are poorly understood.

Purpose of the Study:

• To constrain the depth and properties at the top of Yellowstone's magma reservoir.
• To investigate the state of volatile exsolution and bubble accumulation in the reservoir.

Main Methods:

• Controlled-source seismic imaging to illuminate the magma reservoir's structure.
• Analysis of P-wave and P-to-S-wave reflections to infer fluid/magma properties.
• Comparison of seismic data with tomographic models and dynamic modeling.

Main Results:

• A sharp, reflective cap of the magma reservoir is identified at approximately 3.8 km depth.
• The reservoir cap contains a mixture of supercritical fluid and magma, indicating bubble exsolution and partial retention.
• Seismically estimated bubble volume fraction is lower than pre-eruptive conditions, suggesting efficient bubble escape.

Conclusions:

• Yellowstone's magma reservoir is likely crystal-rich with ongoing magma supply.
• Efficient bubble ascent into the hydrothermal system promotes reservoir stability.
• The current state suggests a stable system with high fluxes of magmatic volatiles escaping to the surface.