Nanoscale silicate melt textures determine volcanic ash surface chemistry

Area of Science:

• Geochemistry
• Volcanology
• Materials Science

Background:

• Explosive volcanic eruptions generate silicate ash with surfaces altered during atmospheric transit.
• Altered ash surfaces influence environmental interactions like ice nucleation and biota toxicity.
• Previous studies assumed ash surface chemistry matched bulk composition due to unknown initial states.

Purpose of the Study:

• To investigate the initial surface chemistry of ash particles generated by controlled volcanic fragmentation.
• To determine if fragmentation creates ash particles with differing surface chemistries compared to bulk composition.

Main Methods:

• Controlled fragmentation of andesite volcanic material.
• Analysis of the surface chemistry of generated ash particles.

Main Results:

• Fragmentation produces ash particles with significant differences in surface chemistry.
• Nanoscale melt heterogeneities, specifically Fe-rich nanophases, influence fracture propagation during fragmentation.
• Pre-eruptive microtextures can alter fracture paths, leading to primary discrepancies in ash surface chemistry.

Conclusions:

• Volcanic ash surface chemistry is not equivalent to bulk composition immediately after fragmentation.
• Melt heterogeneities and pre-eruptive microtextures are key factors controlling initial ash surface chemistry.
• These findings are essential for understanding the environmental consequences of reactive volcanic ash.