A Geologic “Speedometer” for Timing Volcanic Eruptions

Illustration of the piston cylinder apparatus Prissel and colleagues used to conduct their diffusion experiments at high pressures (up to 4 GPa) and high temperatures (up to 1500°C). These pressures and temperatures are relevant to magmatic processes and volcanic systems. Credit: Kelsey Prissel.

Volcanic eruptions represent one of the more rapidly occurring geologic processes, compared to mountain building and plate tectonics. To study the timing of volcanic activity, geoscientists can use the rates of chemical diffusion observed in rock-forming minerals. By measuring how fast elements can mix within or between minerals, the time between eruption of lava and the preceding disturbance that caused the eruption can be determined. New research led by Kelsey Prissel of Washington University in St. Louis presents the first experimentally determined iron-magnesium and iron-manganese inter-diffusion rates for the oxide mineral ilmenite. Ilmenite is a common accessory mineral in many volcanic samples, including those from the Mount St. Helens volcano and diamond-bearing kimberlites. Prissel equates the diffusion process in rocks and minerals to an hourglass, “Whenever an event happens — whether it’s a heating event, pressure change, or new pulse of magma — it’s like you’ve flipped the hourglass over. The sand starts falling as a reaction starts happening in the materials inside the volcano. When the volcano erupts, the reaction stops, and the hourglass is frozen in time. This lets us see how much time elapsed between the initial event and the eruption.” Prissel notes that given enough time without an eruption event to stop the reaction, the hourglass will run out and an accurate record of time is therefore lost — this is equivalent to when a mineral reaches chemical equilibrium. The fast rates of diffusion in ilmenite relative to other minerals means that this new geospeedometer can be used to study magmatic events and volcanic eruptions that took place over the course of a day to a year. READ MORE