volcanic gases[väl′kan·ik ′gas·əz]
gases formed during and after an eruption from a crater, crevices on the sides of volcanoes, and lava flows and pyroclastic rock. The gases emitted during a crater eruption are called eruptive gases, and all others, which are emitted during periods of quiet volcanic activity in the form of streams and swirling masses (from various sections of the crater or from the surface of lava flows), are called fumarole gases.
Eruptive gases determine the character of explosive eruptions and influence the flow of molten lava. These gases contain vapors of H2O, H2 HCl, HF, H2S, CO, and CO2 and small amounts of volatile compounds, mainly halogen compounds of many elements. Fumarole gases are mixtures of gases emitted from lava or pyroclastic rock with gases captured from the atmosphere, formed as a result of their reaction with organic substances found under the hot lava flows or the pyroclastic deposits.
Volcanic gases form numerous hot springs as they pass through the zone of underground waters.
REFERENCESBasharina, L. A. “Vulkanicheskie gazy na razlichnykh stadiiakh aktivnosti vulkanov.” In the collection Tr. laboratorii vulkanologii AN SSSR, issue 19. Moscow, 1961.
Iwasaki, I. [et al.]. “Nature of Volcanic Gases and Volcanic Eruption.” Bulletin Volcanologique, 1963, vol. 26.