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Vapor segregation and loss in basaltic melts

¹ Hawaiian Volcano Observatory, U.S. Geological Survey, 51 Crater Rim Drive, Hawaii National Park, Hawaii 96718, USA
² Cascades Volcano Observatory, U.S. Geological Survey, 1300 SE Cardinal Court #100, Vancouver, Washington 98683-9589, USA

Measurements of volcanic gases at Pu'u‘’, Kilauea Volcano, Hawai'i, reveal distinct degassing regimes with respect to vapor segregation and loss during effusive activity in 2004–2005. Three styles of vapor loss are distinguished by the chemical character of the emitted volcanic gases, measured by open path Fourier transform infrared spectroscopy: (1) persistent continuous gas emission, (2) gas piston events, and (3) lava spattering. Persistent continuous gas emission is associated with magma ascent and degassing beneath the crater vents, then eruption of the degassed magma from flank vents. Gas piston events are the result of static gas accumulation at depths of 400–900 m beneath Pu'u‘’. A CO₂-rich gas slug travels up the conduit at a few meters per second, displacing magma as it expands. Lava spattering occurs due to dynamic bubble coalescence in a column of relatively stagnant magma. The large gas bubbles are H₂O rich and are generated by open-system degassing at depths of <150 m. Static gas accumulation and dynamic bubble coalescence are both manifestations of vapor segregation in basaltic melts, but their implications differ. Accumulation and segregation of CO₂-rich vapor at depth does not deplete the melt of H₂O (required to drive lava fountains near to the surface) and therefore gas piston events can occur interspersed with lava fountaining activity. Lava spattering, however, efficiently strips H₂O-rich vapor from magma beneath the crater vents; the magma must then erupt effusively from vents on the flank of the cone.

Key Words: Hawai'i • Kilauea • magma degassing • vapor segregation • basalt • open path Fourier transform infrared spectroscopy

This article has been cited by other articles:

				M. Edmonds New geochemical insights into volcanic degassing Phil Trans R Soc A, December 28, 2008; 366(1885): 4559 - 4579. [Abstract] [Full Text] [PDF]