The initial cooling of pahoehoe flow lobes |
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| Authors: | Laszlo Keszthelyi Roger Denlinger |
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| Institution: | (1) Hawaiian Volcano Observatory, United States Geological Survey, P.O. Box 51, Hawaii Volcanoes National Park, HI 96718, USA, US;(2) Hawaii Institute for Geophysics and Planetology, SOEST, 2525 Correa Road, Honolulu, HI 96822, USA Fax: +808–967–8890 E-mail: lpk@soest.hawaii.edu, US |
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| Abstract: | In this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows. The accurate modeling of this
initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as
well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation.
This model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not
an empirical fit to field data. We find that the only significant processes are (a) heat loss by thermal radiation, (b) heat
loss by atmospheric convection, (c) heat transport within the flow by conduction with temperature and porosity-dependent thermal
properties, and (d) the release of latent heat during crystallization. The numerical model is better able to reproduce field
measurements made in Hawai'i between 1989 and 1993 than other published thermal models. By adjusting one parameter at a time,
the effect of each of the input parameters on the cooling rate was determined. We show that: (a) the surfaces of porous flows
cool more quickly than the surfaces of dense flows, (b) the surface cooling is very sensitive to the efficiency of atmospheric
convective cooling, and (c) changes in the glass forming tendency of the lava may have observable petrographic and thermal
signatures. These model results provide a quantitative explanation for the recently observed relationship between the surface
cooling rate of pahoehoe lobes and the porosity of those lobes (Jones 1992, 1993). The predicted sensitivity of cooling to
atmospheric convection suggests a simple field experiment for verification, and the model provides a tool to begin studies
of the dynamic crystallization of real lavas. Future versions of the model can also be made applicable to extraterrestrial,
submarine, silicic, and pyroclastic flows.
Received: 26 November 1994 / Accepted: 1 December 1995 |
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| Keywords: | Key words Lava Cooling Pahoehoe Hawai'i |
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