The Year Leading to a Supereruption.

Area of Science:

• Volcanology
• Geochemistry
• Crystallography

Background:

• Supereruptions rapidly eject vast magma volumes, posing significant geological hazards.
• Understanding pre-eruptive magmatic processes is crucial for predicting eruption timing.

Purpose of the Study:

• To determine the timescales of quartz crystallization in the Bishop Tuff magma body.
• To assess the transition from pre-eruptive quiescence to rapid eruption.

Main Methods:

• Utilized synchrotron-based X-ray microfluorescence for quantitative titanium (Ti) mapping in quartz.
• Employed scanning electron microscopy (SEM) with cathodoluminescence (CL) imaging for high-resolution analysis of quartz crystal rims.
• Applied a 1D diffusion model to calculate Ti diffusional relaxation times and quartz growth rates.

Main Results:

• Distinctive, Ti-rich quartz rims formed rapidly, with maximum growth times ranging from minutes to 35 years, but a median of approximately 4 days.
• Over 70% of quartz rims show growth within one year prior to eruption.
• Calculated minimum quartz growth rates indicate very fast crystal growth (100s of nm to 10s of μm per day).

Conclusions:

• Quartz rim growth occurred predominantly in the days to months preceding the Bishop Tuff eruption.
• Rapid rim growth signifies the onset of magma decompression and the transition to syn-eruptive conditions.
• These findings provide critical insights into the short timescales of supereruption preparation.