The Yih Instability in Layered Lava Flow May Initiate the Pāhoehoe to ‘a‘ā Lava Transition

Abstract

After erupting, liquid-like, low-viscosity pāhoehoe flows can sometimes, but not always, transition abruptly into clinkery, high-viscosity lava called 'a'ā. Prior research shows that crystal load is one of the primary physical differences between the two flow types (Cashman et al., 1999;Macdonald, 1953;Washington, 1923). For example, solidified pāhoehoe is more finely grained at flow surfaces than in flow interiors (Katz, 1997) and solidified 'a'ā has a uniform texture (