HR: 15:25h
AN: V13G-08    [Abstracts]
TI: The composition of volcanic gas issuing from Pu`u `O`o, Kilauea Volcano, Hawaii, 2004-5
AU: * Edmonds, M
EM: medmonds@usgs.gov
AF: US Geological Survey, Hawaiian Volcano Observatory, 51 Crater Rim Drive, Hawaii National Park, HI 96718 United States
AU: Gerlach, T M
EM: tgerlach@usgs.gov
AF: US Geological Survey, Cascades Volcano Observatory, 1300 SE Cardinal Court #100, Vancouver, WA 98683 United States
AU: Herd, R A
EM: rherd@usgs.gov
AF: University of Hawaii, Hawaiian Volcano Observatory, 51 Crater Rim Drive, Hawaii National Park, HI 96718 United States
AU: Sutton, A J
EM: ajsutton@usgs.gov
AF: US Geological Survey, Hawaiian Volcano Observatory, 51 Crater Rim Drive, Hawaii National Park, HI 96718 United States
AU: Elias, T
EM: telias@usgs.gov
AF: US Geological Survey, Hawaiian Volcano Observatory, 51 Crater Rim Drive, Hawaii National Park, HI 96718 United States
AB: The eruption of lava is accompanied by prodigious quantities of volcanic gases at Kilauea Volcano. Although sophisticated gas monitoring methods have been implemented at Pu`u `O`o, it is logistically difficult to gather data regularly on the full suite of volcanic gases emitted from crater and flank vents. Since March 2004, Open Path Fourier Transform Infrared Spectroscopy has been carried out, using incandescent vents as a source of infra red (IR) radiation. Strong IR sources, high gas concentrations and short optical pathlengths allow the regular determination of 7 volcanic gas species from vents which are usually too dangerous to approach for direct gas sampling. The data show that a) the gas composition exhibits a significant amount of variation over time and b) different crater vents, just 40-100 metres apart, emit different gas compositions and the gas composition is generally highly variable spatially around the cone and upper flow-field degassing sources (vents, skylights, hornitos). The main degassing site within Pu`u `O`o, the East Pond vent, has emitted gas of a very similar composition to that measured in 1983-5, throughout most of 2004-5: typically 75-85 mol% H<sub>2</sub>O, 10-13% SO<sub>2</sub>, 0.1-3.0% CO<sub>2</sub>, 0.3-0.6% HCl, 0.1-0.5% HF, 0.1-0.8% H<sub>2</sub>S and 0.015-0.025% CO. The most highly variable species over time and space are CO<sub>2</sub>, HF, H<sub>2</sub>S and CO. Data collected during February 2005 show cyclic variations in gas composition during lava spattering activity, which occurred every 10-20 minutes at the East Pond vent inside the crater of Pu`u `O`o. The volcanic gas was rich in CO₂, HCl, H₂S and CO during and immediately after the spatter episode, which involved the spray of lava from the vent 10-30 metres into the air. During the next 10-15 minutes, after spattering, the volcanic gas gradually became more water-rich, it lost its CO₂ and H₂S components and the HCl/HF ratio decreased. We interpret these changes to be due to the upward migration of discrete bubbles from tens of metres depth beneath the volcanic vent, which burst at the surface and cause expulsion of lava and gas. Between larger, deep-derived bubbles bursting at the surface, degassing, of mainly water, takes place from the topmost part of the magma column.
DE: 8419 Volcano monitoring (7280)
DE: 8425 Effusive volcanism
DE: 8430 Volcanic gases
DE: 8486 Field relationships (1090, 3690)
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005