A type of lava flow which spreads in sheets, associated with highly fluid, basic lava, such as that ejected from Hawaiian volcanoes. The surface is a glassy layer which has been dragged into ropy folds by the movement of the hot lava below it. Whether the lava is aa or pahoehoe depends mainly on viscosity and strain rate, which in turn depend on crystallinity, dissolved gas content, temperature, bubble content, slope, eruption rate, and lava composition. See Self et al. (2005) at OpenGeoscience 1 5, 283.

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