281-11 Effect of Wind Speed and Physical Properties on the Convective Cooling of Volcanic Rocks

Session: Petrology, Volcanology, and Mantle Plumes across the Solar System, Part II

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Abstract:

Accurate modeling of lava flows is vital for hazard forecasting and understanding eruption dynamics and emplacement, so it is important to understand cooling rate and the controlling heat transfer mechanisms. A source of uncertainty is the convective heat flux coefficient which is not a constant and cannot be directly measured but depends on environmental conditions. We are interested in the effect of material composition, density, and porosity on the convective coefficient and material cooling. The samples analyzed include the Chao dacite coulee (Chile), Chillahuita dacite torta dome (Chile), Tocorpuri rhyodacite torta dome (Chile), Volcan San Pedro basaltic andesite (Chile), Carrizozo basaltic lava flow (NM), McCarty’s basaltic lava flow (NM), Paxton Springs basaltic lava flow (NM), Medicine Lake obsidian lava flow (CA), Los Chocoyos rhyolitic pumice (Guatemala), and Bishop Tuff rhyolitic ignimbrite (CA). Each sample was measured for density, heat capacity, and thermal diffusivity. Roughly 5 cm cubes were cut, with the top surface being the original sample surface. Cubes were heated to 500˚C in a furnace, then removed and placed under a T1020 Forward-Looking Infrared (FLIR) camera to record a timelapse of their cooling. Experiments were conducted for free and forced convection, with a leaf blower being used to produce windspeeds up to 20 ms^-1. A simple thermal model (Qrad + Qconv + Qcond = Cp * DT) of the cooling includes radiation, conduction, and convection fluxes. All the model components are constants, directly measured, or calculated from measured values, except for the convective heat flux coefficient. A coefficient value was determined for 20, 15, 10, and 5 ms^-1 wind speeds and free cooling for each sample. While the spread in coefficient values increases with increasing wind speed, the averages show a strong linear trend, hc ≈ 9.5 x wind speed (ms^-1). Higher porosity samples may experience greater variability in cooling from physical interactions between pores and wind currents. Free convection coefficient values are low (<10 Wm²K^-1) and appear independent of porosity. For forced convection, the coefficient ranges from 40 Wm^-2K^-1at 5 ms^-1 to 250 Wm^-2K^-1 at 20 ms^-1 and appears to increase for higher porosities. Improving understanding of convective heat transfer will allow for better modeling of present and historical flows for existing and future lava flow models.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9657

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