HR: 09:48h
AN: V31D-10 INVITED     [Abstracts]
TI: Field Experiments on Active Kilauea Lava Flows to Improve Cooling Models for Pahoehoe Lava Flows
AU: * Keszthelyi, L
EM: laz@usgs.gov
AF: USGS, Astrogeology Team, Flagstaff, AZ 86001 United States
AU: Thornber, C
EM: cthornber@usgs.gov
AF: USGS, Cascades Volcano Observatory, Vancouver, WA 98683 United States
AU: Harris, A
EM: harris@higp.hawaii.edu
AF: Hawaii Institute for Geology and Geophysics, University of Hawaii at Manoa, Honolulu, HI 96822 United States
AU: Sharma, K
EM: k.sharma@open.ac.uk
AF: Department of Earth Sciences, Open University, Milton Keynes, MK7 6AA United Kingdom
AB: Previous attempts to model the cooling of pahoehoe lava flows have shown that uncertainties in the cooling by the wind and non-equilibrium crystallization caused significant errors. New analyses of field data collected over the past decade from active pahoehoe flows on Kilauea Volcano, Hawaii, have helped reduce these uncertainties. Field measurements of the cooling of pahoehoe surfaces by the wind show that the heat transfer coefficient to the atmosphere is 45-50 W m$^{-2}$ K^{-1}$ at a wind speed of 10 m/s and a surface temperature of 500 $\deg$C. This is consistent with earlier field data, but is more than 5 times higher than predicted by theory. We also find that cooling by the wind is the most inefficient when there is a slight breeze, rather than in still air. This may be because the convective patterns that would be set up in still air are disrupted by a breeze. Another field experiment quenched small pahoehoe lobes at different points in their cooling histories by cutting them off with an ax and dumping them into a bucket of water. The lobes were instrumented with thermocouples and cooled naturally for 370-2500 s before quenching. From these lobes we have produced a series of thin sections for which we have measured cooling histories. We find that the observed crystallinity can be adequately modeled as a function of either cooling rate or undercooling, but the the abundance of pre-existing nucleation sites is a critical parameter. In general, glass is formed at cooling rates above 1-3 $\deg$C/s. Initial undercooling of the lava was approximately 2-8 $\deg$C. Finally, the drilling of a 1.5 m thick inflating pahoehoe flow provides direct views into a flow that is intermediate in size between small pahoehoe lobes and flood basalt lava flows. From this experiment, we can constrain the growth of the upper crust as a function of time, when bubbles grew and migrated in the lava, and the overpressure during inflation. These field observations are being incorporated into an improved numerical model for the cooling of pahoehoe lava flows of all thicknesses.
DE: 8429 Lava rheology and morphology
DE: 8494 Instruments and techniques
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting