The chemical behaviour of sulphur in magmas at high temperature and pressure

The aim of this project is to develop a clear understanding of the behaviour of the element sulphur in volcanoes and in the gases which are expelled from volcanoes during and prior to volcanic eruptions. Volcanoes have important effects on both their local and global environments. In the global context they emit large clouds of ash and polluting gases particularly sulphur in the form of sulphur dioxide. Both ash and sulphur dioxide have the effect of cooling the atmosphere. During the 1991 eruption of Mt Pinatubo in the Philippines, for example 18 million tons of sulphur dioxide were emitted and cooling of the atmosphere at ground level lasted 1-3 years. A more extreme example is the eruption of Mt Tambora (Indonesia) in 1815. This produced 120 million tons of sulphur dioxide which led to the "year without summer" of 1816. In the Northern Hemisphere in 1816 crops failed, livestock died and many people starved. Such eruptions with similar or greater climatic effects can be expected episodically in the future despite the long-term trend of increasing global temperatures. Understanding how and why sulphur dioxide is emitted during volcanic activity is, therefore, central to this project. Despite the environmental importance of such emissions from volcanoes it is surprising that there is little information available on the extent to which sulphur dioxide dissolves in volcanic liquids (lavas) prior to and during eruption. One of the aims of the project is therefore to determine how much of the gas is dissolved in lavas at high pressures deep in the Earth's crust and how much is degassed to the atmosphere as the lava moves from deep in the crust to just underneath the volcano. This will enable geologists to connect the amounts of lava erupted as liquid and ash to the anticipated climatic effects in the form of sulphur dioxide emitted.

A second aim of the project is to determine the conditions under which economically important deposits of sulphur-rich ore minerals occur in association with volcanic activity. Geologists know the kinds of environment in which these deposits occur, but there are still unresolved questions about the depths at which the ore minerals become stable. Are, for example, economically important deposits more likely to be found if the crust is thin or thick in the area of interest? By performing experiments at different pressures, simulating different crustal thicknesses, this project aims to answer that question.