The initial cooling of pahoehoe flow lobes

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(Jones , 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.

Terrestrial analogs and thermal models for Martian flood lavas

“…where h is the atmospheric heat transfer coefficient, which has an approximate value of 70 W m '2 K 'l on the Earth [Keszthelyi and Denlinger, 1996]. This value should be directly proportional to atmospheric density and heat capacity [e.g., Arya, 1988], suggesting a value of-1 for Mars.…”

Observations and initial modeling of lava‐SO2 interactions at Prometheus, Io

“…As described by Turcotte and Schubert [1982] and modified for crystallinity by Keszthelyi and Denlinger [1996] [Keszthelyi, 1994] Ru=2(I, 6 6or/3 , …”

Extended SO2 outgassing from the 2014–2015 Holuhraun lava flow field, Iceland

“…Keszthelyi and Denlinger, 1996;Wooster et al 1997;Cashman et al 1999;Patrick et al 2004;Kolzenburg et al 2016). Lava flows cool by thermal radiation and atmospheric convection from the surface and by conduction to the underlying country-rock (Keszthelyi and Denlinger, 1996;Neri, 1998;Patrick et al 2004).…”

“…Lava from the Holuhraun eruption had up to 45% vesicles (Lavallée et al 2015). This high vesicularity is likely to have enhanced the cooling of the flows as lava porosity is considered to affect the rate of cooling, with more vesicular lava cooling more rapidly (Keszthelyi and Denlinger, 1996).…”

“…We additionally discuss the physical processes of cooling and fracturing (e.g. Keszthelyi and Denlinger, 1996;Kattenhorn and Schaefer, 2008;Patrick et al 2004;Wittmann et al 2017) that contribute to post-emplacement lava outgassing.…”