Thermal properties of vesicular rhyolite
b'Thermal diffusivity of rhyolite melt and rhyolite foam (70\\u201380% porosity) has been measured using the radial heat transfer method. Cylindrical samples (length 50\\u201355 mm, diameter 22 mm) of rhyolite melt and foam have been derived by heating samples of Little Glass Mountain obsidian. Using available data on heat capacity and density of rhyolite melt, the thermal conductivity of samples has been determined. The difference in thermal conductivity between rhyolite melt and foam at igneous temperatures ( 1000\\xb0C) is about one order of magnitude. The effect of thermal insulation of magmas due to vesiculation and foaming of the top layer is discussed in terms of the data obtained using a simple illustrative model of magma chamber convection.'