Kinematics of lava flows based on fold analysis

Abstract

A kinematic analysis of the mingling-folding structures occurring in a lava flow from Porri volcano (Southern Tyrrhenian Sea) has been performed in order to estimate the flow kinematic parameters. Folds have resulted from the deformation of enclaves and banding structures, and consist of a single layer of a crystal-rich andesitic magma hosted in a less competent basaltic magma. Results of the analysis indicate that the flow kinematic vorticity increases with the distance from the vent, whereas the ratio between pure shear and simple shear strain decreases following a power law. Quantitative estimates of the kinematic parameters provide an opportunity to examine the deformation behaviour of the lava flow. Near the vent, the lava is a non-ideal shear flow; away from the vent, the lava is an ideal shear flow. Gravity-driven mechanisms control the relative contribution of pure and simple shear to the bulk deformation.