Effects of internal rheology and surface cooling on the emplacement of lava flows

Abstract

The emplacement dynamics of lava flows is modeled using a combination of laboratory experiments and theoretical scaling analyses for the case where a fixed volume of lava is rapidly released and spreads as a horizontal, two-dimensional flow. We focus on the processes that determine the final runout length of the lava, including the growth of a crust due to surface cooling and the presence of an internal yield strength. We show that solidifying flows with no internal yield strength first spread in slumping and viscous flow regimes, before a final regime where the yield strength of the growing crust stops the flow. We then demonstrate that solidifying flows with an internal yield strength can be stopped by either the internal yield strength or the growing crust. We also find that the yield strength of the solidified crust systematically increases with increasing internal yield strength. We illustrate our results by predicting the flow regimes of two typical lavas: a Hawaiian lava with no interior yield strength and a Mount Etna lava with an interior yield strength. In particular, we find that the crust strength stops small volume breakouts of the Mount Etna lava, while large volume breakouts are stopped by the interior yield strength.