Abstract
Volcanic fissure eruptions transition from magma extrusion along long cracks to discrete vents within hours or days. Flow localisation is facilitated by variations in fissure geometry and host rock temperature along the crack. Variable cooling and blockages along the fissure direct flow into areas that remain open. We present a new experimental program aimed at investigating the thermal feedbacks that occur during cooling and flow localisation once a fissure eruption is underway, and the sensitivity of the system to changes in fissure shape and wall temperature. We have built a model volcanic fissure with adjustable shape, width, and wall temperature. We use Polyethylene Glycol (PEG) 600, a type of wax, as a low-temperature analogue fluid, which is injected into the slot from a pump with variable speed drives. This allows fluid flux to also be changed or paused during an experiment. Understanding how wall-rock properties influence conduit initiation will assist hazard modellers in determining future eruption evolution and likely vent locations. Initial tests prove the function of the device, showing that the key variables can be changed and that localisation in various conditions can be achieved. Video is used to record the physical changes in the PEG as it flows, cools and solidifies, while continuous wall temperature data show initial high rates of heat transfer into the wall before an insulating solid wax layer forms. The wax also carries particle tracers from which flow patterns and rates can be determined as the fluid moves around obstacles, is channelled into a conduit, and flow rate decreases during solidification. The apparatus is housed at the University of Otago, New Zealand. The device is the focus of an experimental program running over several years, but it may be adapted for other experiments on fluid flow behaviour in non-planar slots and variable temperature conditions.