Reexamining the Potential to Characterize Lava Flows from Margin Geometry

Abstract:

Previous work has suggested that the fractal analysis of a lava flow’s plan-view margin has the potential to constrain the morphologic type (e.g., pāhoehoe) and chemical composition (e.g., basaltic) of the flow. These constraints could, in turn, provide insights into the rheology and dynamics of the flow at the time of its emplacement. Furthermore, previous work has suggested that measured margin fractality may be scale-invariant, which would allow this interpretive technique to be applied to margins observed exclusively in remotely-sensed data, regardless of resolution. That potential would be essential to planetary applications, where field access is normally impossible and data resolution varies with instrument and viewing geometry. However, in the absence of ground truth to aid interpretation, the reliability of this technique would depend on three hypotheses: (1) measured lava margin fractality is generally scale-invariant; (2) different flow types and compositions are consistently distinguishable based on their measured fractality alone; and (3) any geometric modification by unobserved contexts, including sloped substrates and topographic confinement, does not impede interpretation. In the present study, we critically evaluate each of these hypotheses using 15 field-collected margin intervals from a wide variety of lava flow types in Hawaiʻi, Iceland, and Idaho. Based on these investigations, we reject each hypothesis at meter-scales. We therefore conclude that the interpretation of lava flow type and composition based on fractal analysis at meter-scales is not reliable.