Obsidian Clasts Research Articles

Magmatic volatiles in explosive rhyolitic eruptions

Obsidian clasts in rhyolitic tephra deposits preserve preemption magmatic volatile contents, providing a direct means for determining the volatile content of explosively erupted magmas. Small to moderate volume Plinian eruptions (10−3 to 10−1 km³) appear to be driven by 0.5‐1.0 wt.% volatiles, consisting dominantly of H2O with minor CO2. Analysis of obsidian from eruptive sequences consisting of tephra and flows indicates that this hydrous magma abruptly overlies magma with only 0.1‐0.2 wt.% H2O.