University of Tasmania, Australia

Mechanisms and products of seafloor caldera-forming eruptions – Izu-Bonin Arc and Mount Read Volcanics

Eruptions that form calderas on the seafloor are very poorly understood even though their products are very common on the modern seafloor around active arcs and in ancient submarine volcanic successions. Seafloor calderas are also important hosts to modern and ancient massive sulphide deposits. The dynamics of such eruptions are strongly affected by the higher confining pressure, viscosity, density and heat capacity of water compared with air. Detailed textural and compositional study of submarine pyroclastic deposits provides the data required for assessing the influence of these parameters on eruption mechanisms.

This PhD project will explore the key controls on submarine caldera-forming explosive eruptions by

• Measuring the physical and chemical properties of pyroclastic pumice samples recovered from Myojin Knoll caldera in the Izu-Bonin Arc
• Defining the lithofacies characteristics, dimensions and emplacement mechanisms of caldera-related submarine pyroclastic deposits in the Mount Read Volcanics, western Tasmania.

The first dataset helps constrain the timing and mechanisms of volatile exsolution, while the second approach provides a basis for interpreting eruption column behaviour.

The Myojinsho samples have been provided by collaborator, Richard Fiske, Smithsonian Institution. Excellent sections through caldera-related pyroclastic units are available in the Mount Read Volcanics. The project requires a combination of laboratory-based analytical work, and fieldwork, and involves collaborations with the Smithsonian Institution, Washington, and University of Oregon (Kathy Cashman).