page_title: Volcanic gas
hierarchical_section_title: Volcanic gas
caption_attribution_description: Grand Prismatic Spring, Excelsior Group, northern Midway Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA in August 2011. Grand Prismatic Spring is, by far, the most beautiful thing I’ve ever seen. This rainbow-colored hot spring is best appreciated from the boardwalk along the northeastern edge of the pool and from atop Midway Bluff, a hill on the eastern side of the highway next to the Firehole River and from “7622 Hill” on the southeastern side of Fairy Falls Trail/Fountain Freight Road. [7622 Hill is now off limits due to the death of a Taiwanese tourist on the hillside in 2014; a boardwalk leading up to a viewing platform is supposedly being planned.] The deep blue color at the center of the pool is the result of very hot water having abundant, suspended, &lt;0.5 micron-sized, colloidal silica particles. The yellow, orangish, reddish, and brownish areas are mats of extremophile bacteria (e.g., Phormidium, Synechococcus, Calothrix). The greenish areas are the effect of “blue water” mixing with the light reflecting from the yellowish bacterial mats. Grand Prismatic Spring is the largest hot spring in the world. It does not erupt as a geyser.
context_page_description: Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating directly from lava or indirectly through ground water heated by volcanic action.
  The sources of volcanic gases on Earth include:
  primordial and recycled constituents from the Earth's mantle,
  assimilated constituents from the Earth's crust,
  groundwater and the Earth's atmosphere.
  Substances that may become gaseous or give off gases when heated are termed volatile substances.
context_section_description: Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating directly from lava or indirectly through ground water heated by volcanic action.
  The sources of volcanic gases on Earth include:
  primordial and recycled constituents from the Earth's mantle,
  assimilated constituents from the Earth's crust,
  groundwater and the Earth's atmosphere.
  Substances that may become gaseous or give off gases when heated are termed volatile substances.
caption: Degassing at Grand Prismatic Spring, Yellowstone National Park
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