How does topography affect the propagation of magmatic intrusions? An experimental study

Understanding the controls on magma ascent is critical for developing eruption forecasting. The movement of dykes (vertical magma intrusions) through the crust is particularly important to constrain, as often dyke propagation inferred from surface deformation, geodetic inversion techniques and seismicity is used to signify volcanic unrest, potentially leading to evacuation orders and eruption. However, the factors affecting dyke direction, geometry and ascent velocity are still relatively unconstrained.

In this study we explore the topographic loading controls on dyke behaviour. It is impossible to visualise dyke behaviour in natural systems as these processes occur at depth and on large scales, but scaled experimental analogue setups allow us to study the natural world in a laboratory setting, allowing us to make valuable insights into natural processes. We use an analogue setup, with a transparent, gelatine solid as a homogeneous elastic crust injected by dyed water from below as an intruding Newtonian fluid representing magma. The surface of the gelatine was moulded to represent a flat, inclined or ridge topography. Two CCD cameras placed above the experiment measure the vertical and lateral surface displacement created by the intrusion, as a penny-shaped experimental dyke grows. Polarised light is used in order to visualise the evolving stress field within the gelatine solid, recorded by an HD camera positioned at the side of the tank. Multiple injection points were used to vary the location of dyke initiation and their interactions with topography and previous injections. These experiments allow us to measure the 3D intrusion geometry, tip velocity, extent of surface deformation and rate, and relate these to the gelatine’s evolving internal stress field. Preliminary results indicate that topography does have an effect on dyke propagation, producing dyke bending, rotation and changing ascent velocity.

By understanding the topographic controls on dyke behaviour, we can better identify areas more likely to experience magmatic intrusions at volcanic systems worldwide, which has important implications for hazard mapping and managing volcanic risk.