Volcanic flows

In this chapter, we use a fluids perspective to survey the life cycle of magma (molten rock) from its origin at depth to its ascent through volcanic conduits, its eruption into the atmosphere, and its flow across the Earth’s surface. Each of these stages involves strong gradients in temperature, pressure, chemical composition, and rheology, leading to a dizzying number of variables and highly complex boundary conditions. Geologists must simplify these systems in their analytical and numerical models, in order to come up with useful relationships that can help determine the beginning, end, and intensity of eruptions. Here we describe a sampling of this fascinating set of behaviors, organized into three sections: (1) What happens at depth where magma forms, mobilizes, and rises to the surface, (2) what takes place when gas-rich magma erupts explosively, and (3) what occurs during relatively quiet effusive eruptions that produce lava flows and domes (Figure 16.2). In each section, we begin with a description of the geologic phenomena, then outline the relevant physical processes, and end with a few specific examples of how knowledge of fluid dynamics can help us interpret the geologic record and predict transitions in eruption style.