Magma Degassing and Controls on Eruption Style

Volcanoes around the world exhibit a large range in eruption styles, some producing violent ash-rich explosions, whereas others rather passive lava flows or domes. Changes in eruption magnitude and style may also occur at individual volcanoes, increasing the challenge of forecasting. Volatiles, dissolved and exsolved, are the main drivers of volcanic eruptions and their loss or retention during magma ascent ultimately controls the style of an eruption. This project investigates the dynamics of magma degassing, in the conduit and in the reservoir, using a range of methods going from geochemistry to numerical modeling. Applying them to case studies such as Merapi (Java), Rabaul (PNG) and Pinatubo (Philippines) should shed light on the relative importance of reservoir versus conduit dynamics on controlling the eruption style.

Dynamics of magma degassing in the reservoir (P, T, composition, volatile content & presence of a pre-eruptive exsolved volatile phase) are investigated at Rabaul and Pinatubo with detailed melt inclusion and S-isotope studies. Conduit dynamics and their complex feedbacks are investigated at Merapi and Rabaul through combined studies of microlite number densities and size distributions - yielding information on magma ascent and volatile exsolution rates - and clast porosities, permeabilities, and bubble network geometries - yielding information on permeable gas escape. These results will then feed various numerical models that will explore transitions in eruption style during and between eruptive episodes and the recurrence of centennial events.

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