(0.001 Pa·s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines, lava domes or "coulees" (which are thick, short lava flows). The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian.

Felsic magmas can