HR: 0800h
AN: V21A-0382    [Abstracts]
TI: Morphology and Emplacement of the Muliwai a Pele Lava Channel, Mauna Ulu (Kilauea, Hawai'i)
AU: * Harris, A
EM: harris@higp.hawaii.edu
AF: HIGP/SOEST, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AU: Rowland, S
EM: scott@soest.hawaii.edu
AF: G&G/SOEST, University of Hawaii, 1680 East-West Road, Honolulu, HI 96822, United States
AB: The 5.6 km-long Muliwai a Pele lava channel formed during one of the last stages of Kilauea's 1969 - 1974 Mauna Ulu eruption, specifically during a fountaining event of May 29 - June 2, 1974. We have mapped the entire channel to define spatial and temporal variations in channel construction, and their influence on the final channel form. The levee sequence comprises a basal 'a'a unit covered by pahoehoe overflow units. Morphologically the channel can be split into five down-channel sections: (1) 0 - 1.1 km: Tubed - The channel initiates as a notch in Mauna Ulu's south wall. Along this section, a braided tube system has developed; its line marked by surface collapse depressions and skylights. (2) 1.1 - 3.1 km Proximal - Along this section the channel is 3 to 11 m wide (mean = 9 m), and 2 to 6 m deep (mean = 3 m). The mean depth compares with a mean flow thickness of 4 m. The channel floor comprises undrained lava within which a tube developed and locally collapsed. Channel overflows are dominated by thin (1 - 20 cm), smooth surfaced, vesicular (53 - 58 %), pahoehoe sheets. These are of limited extent, extending no more than a few 10's of meters from the channel, but were able to bury the basal 'a'a entirely. (3) 3.1 - 4.1 km Medial I - Along this section blockages become common, with 8 occurring within this 1 km distance. Blockages are composed of levee chunks plucked from the up-flow channel walls. They are porous so lava flowed through them as well as around them. Behind each blockage, relatively viscous and dense (40-48 % vesicles) lava became ponded. In places this overflowed to feed flows with spiny-pahoehoe-to-'a'a surfaces. (4) 4.1 - 5.1 km Medial II - Along this section surge-fed overflows evolve into denser (40 - 50 % vesicularity), more viscous-appearing surface forms. Overflows are no longer smooth, and instead have spiny textures that transition into localized 'a'a swirls. The drained channel depth (mean = 10 m) is deeper than the sequence thickness (mean = 9 m), and the channel width varies between narrow (7-14 m wide) and broad (15-25 m wide) sections as the underlying slope begins to steepen. The over-deepening may be the result of thermal and mechanical erosion. (5) 5.1 - 5.6 km Distal - Over this section the channel descends the steep (20-30 °) slopes of Poliokeawe Pali, at the base of which the channel dies out to feed ~2.8 km of dispersed 'a'a flow. The channel features indicate variable supply over the course of emplacement, resulting in a three-stage construction process. First, a high effusion rate phase emplaced a basal 'a'a unit, that crops out along most of the medial section. Within this basal unit the channel developed. For the majority of the channel's life, lower-flux (<10 m³ s^-1) flow dominated, and localized tubes developed under and between ponds of viscous lava collecting between blockages. Occasionally, short-lived (~100 ³ s^-1) surges emplaced fluid, vesicular lava to build pahoehoe overflow units. These surges also transported blockage material.
DE: 8400 VOLCANOLOGY
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8425 Effusive volcanism
DE: 8429 Lava rheology and morphology
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting