Editing Magma (section)

==== Felsic magmas ====
''Felsic'' or [[Silicon dioxide|silicic]] magmas have a silica content greater than 63%. They include [[rhyolite]] and [[dacite]] magmas. With such a high silica content, these magmas are extremely viscous, ranging from 10<sup>8</sup> [[centipoise|cP]] (10<sup>5</sup> Pa⋅s) for hot rhyolite magma at {{cvt|1200|C||}} to 10<sup>11</sup> cP (10<sup>8</sup> Pa⋅s) for cool rhyolite magma at {{cvt|800|C||}}.{{sfn|Philpotts|Ague|2009|p=23}} For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce [[Pyroclastic rock|pyroclastic]] (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form [[lava spine]]s, [[lava dome]]s or "coulees" (which are thick, short lava flows).{{sfn|Philpotts|Ague|2009|pp=70-77}}  The lavas typically fragment as they extrude, producing [[Lava#Block lava flows|block lava flow]]s. These often contain [[obsidian]].{{sfn|Schmincke|2003|p=132}}

Felsic lavas can erupt at temperatures as low as {{convert|800|°C}}.{{sfn|Philpotts|Ague|2009|p=20}} Unusually hot (>950&nbsp;°C; >1,740&nbsp;°F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the [[Snake River Plain]] of the northwestern United States.<ref>{{cite journal |last1=Bonnichsen |first1=B. |last2=Kauffman, D.F. |year=1987 |title=Physical features of rhyolite lava flows in the Snake River Plain volcanic province, southwestern Idaho |journal=Geological Society of America Special Paper |series=Geological Society of America Special Papers |volume=212 |pages=119–145|doi=10.1130/SPE212-p119 |isbn=0-8137-2212-8 }}</ref><!-- Rather an old source; are the Snake River flows still regarded as fluid flows and not ash flows?-->