HR: 09:36h
AN: V31D-09    [Abstracts]
TI: Drilling an Active Pahoehoe Lava Flow
AU: * Thornber, C
EM: cthornber@usgs.gov
AF: U.S. Geological Survey, 1300 SE Cardnal Ct., Vancouver, WA 98683 United States
AU: Keszthelyi, L
EM: Laz@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001 United States
AU: Lewis-Kenedi, C
EM: katelk@duke.edu
AF: Duke University, Div. Earth and Ocean Sciences, Durham, NC 27708 United States
AU: Cazeneuve, M
EM: mcazen@geoteq.com
AF: Geotechnologies, Inc, 439 Western Ave., Glendale, CA 91021 United States
AU: Goehring, D
EM: lavadg@cs.com
AF: American Technologies, Inc., 142 Fairbanks Rd., Oak Ridge, TN 37830 United States
AB: Core-Drilling of an actively inflating pahoehoe lava flow on Kilauea Volcano, Hawaii has provided new insight into the timing and causes of widely recognized petrologic variations within individual basalt flows. Seven closely spaced and successively longer cores through the crust-melt interface, along with melt samples, were recovered from a single lava flow during inflation and then throughout final solidification. Petrologic studies of these melt and core samples have yielded time-constrained vertical profiles of whole-rock, glass and mineral chemistry; glass thermometry and vesicularity. Theodolite measurements document flow inflation to 1.96 m height over the first 9.8 hrs after emplacement, concurrent with sporadic lava breakouts in the immediate vicinity of the drill site. Down-hole depth-profiles obtained at 3.0, 4.4 and 6.5 hrs, reveal steadily increasing upper and lower crustal thickness to 25 cm, while a melt thickness of 1.1-1.2 m was sustained within the inflating flow lobe. The temperature, composition and vesicularity of the upper crust-melt interface and central melt zone remained fairly constant as the flow inflated. However, olivine accumulated toward the base of the flow during this interval of dynamic recharge. As activity waned, the flow deflated for 17 hrs to a final height of 1.56m. Depth-profiles obtained from drilling at total elapsed times of 10.3, 11.1, 27.5 and 72.8 hrs, reveal a steadily diminishing melt thickness during deflation which culminated with a 45 cm, highly viscous zone in the core of the flow. As the melt receded from the deflating lobe, the interior flow cooled at $0.5\deg$C/hr and subsequent closed-system fractionation ensued with slower cooling at $0.2\deg$C/hr. During cooling, vesicles coalesced and migrated, leaving a dense inner flow core. Static processes associated with solidification of the flow core include development of a differentiated plagioclase mush at the flow-core top, an olivine rich layer at the flow-core bottom, and upward infiltration of late-stage residual melt. The flow core was completely solidified within 300 hrs after emplacement, when two final cores were collected. These complete cores allow correlation of the final intra-flow stratigraphy with the progressive changes documented by drilling of the flow while it was active.
DE: 8429 Lava rheology and morphology
DE: 8494 Instruments and techniques
DE: 3625 Descriptive mineralogy
DE: 3640 Igneous petrology
DE: 3655 Major element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting