Numerical simulation of open channel basaltic lava flow through topographical bends

Abstract

In this study, we utilised computational fluid dynamics to investigate the behaviour of open-channel basaltic lava flows navigating bends on shield volcanoes. Our focus was on understanding the relationship between flow velocity, rheology, and bend geometry. Employing a simple Force Balance Model (FBM), which considers the equilibrium between hydrostatic pressure and centrifugal force, we accurately approximated the changes in the height of the lava’s free surface through various bend geometries. Our analysis includes examining the influence of channel depth, width, and bend radius on the flow, revealing that variations in these parameters significantly affect the flow’s vertical displacement. Additionally, the bend sector angle emerged as a critical factor, indicating a minimum angle necessary for the flow to fully develop before exiting the bend.Further, we assessed the applicability of the Shallow Water Equations (SWE) for modelling the inertial displacement of the lava flow in bends, finding a good fit. The study extended to comparing the FBM’s predictions of the tilt angle of the flow’s free surface with the SWE results, showing notable agreement under specific conditions, particularly at a bend angle of 90 degrees. The impact of fluid density was also considered, revealing that density is a contributing factor to the development of the wetted line in the bend, a factor that is not captured by the simple FBM model. Finally, we explored different rheologies akin to natural lava flows, such as viscoplastic flow, and determined that factors like yield stress, consistency index, and power law index have a small impact on the flow behaviour in a steady-state condition within a bend.

Keywords

• Wetted contact line
• Inertial displacement
• Lava rheology
• Shallow Water Equations
• Herschel–Bulkley
• Lava-channel bends