Dynamics of Lava Domes

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

Balmforth 0072521 Lava domes are a common geological formation, and their geometry sets them apart as one of the more simple types of lava flow. Moreover, domes often have a relatively low aspect ratio and evolve slowly. These observations can be used as ingredients in building simple mathematical models of expanding and cooling fluid domes; this proposal surrounds the development of such models. In particular, lava is considered as a solidifying, non-Newtonian fluid with strongly temperature-dependent material qualities and an intrinsic yield stress. The wide array of physical ingredients to the problem make the mathematical modelling especially challenging. The project exploits the simple geometry, slow evolution and low aspect ratio of the dome to asymptotically reduce the governing equations to a simpler form. The reduction furnishes "shallow-lava equations," in much the same way that the "shallow-ice equations" are derived and extensively used to model ice sheets and glaciers. Differences arise because of the viscoplastic nature of silicic lava, and because solidification creates a solid crust overlying the dome that can contribute significantly to the balance of forces, especially at the disk's edge. The mathematical approach are complemented with an experimental one in which laboratory fluids are used as analogue models of the lava. Both approaches are used to explore the structure and evolution of the dome, partly with the aim of learning more about how lava behaves as a fluid. For example, some domes lose axisymmetry in what might be an intrinsic morphological instability; this pattern formation process is explored in that light. Lava domes occur in many geological settings both on Earth and on many other planets and moons of the solar system. These structures form when crystal-rich silicic magma is pushed up through vents onto roughly horizontal surfaces, and often occur inside the craters created by volcanic eruptions. The shape of a lava dome is especially simple in comparison to most other lava flows. Hence, a first step in understanding lava flows in general is to explore those domes. Moreover, despite their slow growth, domes are natural hazards because they can be the setting of violent and dangerous events: domes can rupture and release confined gas in a pyroclastic outflow (an extremely hot and fast-moving current of air and ash), or collapse at their peripheries to create landslides and debris flows. The proposal outlines a mathematical and experimental approach to the modelling of lava domes. The purpose is to build models of the dome's structure and evolution, and compare these models with the real geological structures. By modelling the domes in this way, more will be learned about how lava flows, and ultimately this may provide insight into the hazards associated with them.