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Fracture and Fluid Flow in Volcanic Conduits and Lava Domes

Project: Non-funded ProjectResearch

1/10/1030/09/15

Volcanic eruptions are amongst the most devastating and spectacular natural phenomena. As millions live close to potentially active volcanoes it is essential we fully understand how volcanoes work so that we can predict dangerous changes in activity. Lava dome eruptions are especially hazardous since they are prone to sudden explosions; often the only warning they provide is swarms of tiny earthquakes that occur shortly before explosions. Eruptions of highly-viscous (sticky) rhyolitic magma tend to be the biggest and most destructive, but their character has two sides: they can either be violently explosive or quietly ooze out flows of thick, viscous lava. In the largest known eruptions so much magma is erupted that the ground collapses, forming a huge depression (caldera) many miles across.
All of these phenomena are linked by a simple, common theme, as they all involve the flow of fluids (gas or magma) through cracks in rock (hot new lava or cold older rocks). However, nothing is as simple as it seems. Take earthquakes at lava domes: there is currently heated debate over whether they are triggered by the fracture (cracking) of lava or by gas flowing through the cracks. We suspect that the escape of volcanic gases from rising magma controls the violence of rhyolitic eruptions, and gases probably escape through cracks in the cold rocks around the conduit (vent) feeding magma to the surface, but we are not sure of the details.
How can we resolve these uncertainties? The answer may well lie in the geological record, where old lava domes and lava-filled conduits formed in ancient eruptions have been dissected by erosion. The rocks around conduits are cut by veins metres in length. These are cracks filled by ash that is composed of fine lava fragments. Tiny laminations in the ash show that it was being carried away from the conduit by a flowing fluid – probably volcanic gases that were escaping from the magma. The veins (called tuffisites) therefore provide priceless evidence for the very process that may both control the style of eruptions and trigger volcanic earthquakes.
In my Fellowship I will conduct what will be, remarkably, the first detailed study of tuffisite veins. By carefully measuring the size and shape of ash particles, studying the laminations within veins and measuring the permeability of rock samples I will estimate the rate of gas flow through the veins. I will also measure the concentration of dissolved volcanic gases such as water and CO2 in the ash, as this yields extra information about how much gas was escaping from the rising magma. This work will therefore provide powerful new insights into how gas escape influences the violence of eruptions. My data on the nature of tuffisite veins will also be used in sophisticated models that simulate the earthquakes triggered by gas flow within cracks, and the results compared with measured volcanic earthquakes to determine which trigger mechanism occurred.
Active lava domes will provide an exciting addition to this research. Some domes regularly belch clouds of gas and ash from cracks on their surface, accompanied by shallow earthquakes. This is very similar to what happens deep underground in tuffisite veins, but critically occurs on the surface – allowing us to collect ash samples, record the earthquakes and measure the timescale of the gas escape through cracks. This modern perspective will provide incredibly useful constraints on the processes involved.

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With potential for a three-year extension up until 2018

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