This project is being supported by the Petrology and Geochemistry program (Division of Earth Sciences) and the Africa, Near East & South Asia Program (Office of International Science and Engineering). Sulfur (S) is one of the most abundant constituents of volcanic gases and is an important component of magmas. Sulfur is the most important volcanic gas in terms of climate impact due to the oxidation of sulfur to sulfate aerosols in the atmosphere. Large eruptions like the one at Pinatubo, Philippines in 1991, caused global temperatures to drop by two degrees over a period of two years. Sulfur has recently received a lot of attention due to ideas of geo-engineering where scientists propose to inject large quantities of sulfur into the stratosphere to counterbalance global warming. Therefore, understanding how and in what quantities sulfur degases naturally from magmas at volcanoes is a critical step in evaluating the global sulfur cycle with implications for climate impact as well as evaluating potential consequences of human impacts on the Earth's sulfur budget. In this proposed work, the team aims to investigate sulfur degassing from a persistently active lava lake. The lava lake that is best suited for this project is that of the Erta Ale volcano in Ethiopia. This lake is the Earth's longest-lived lava lake and has been persistently active for over 100 years. It degases large quantities of sulfur from a basaltic magma. They will collect samples of the active lava lake, the degassing sulfur, and the sulfate aerosol formed in the atmosphere. The isotopic composition of the sulfur in the lava, gas, and aerosols will be analyzed to understand the nature of the sulfur cycle.
The ultimate goal of this study is to develop a consistent model for how sulfur degases from magmas in volcanoes worldwide. Fluxes of sulfur dioxide can be measured because their atmospheric concentrations are easily detectable due to its absorption of ultraviolet light. The H2S/SO2 ratio of primary magmatic gases is pressure dependent and therefore can be used as a proxy for depth of degassing. Therefore, degassing of S provides useful insights into volcanic degassing processes, can be used as an indication of increasing or decreasing volcanic activity, and is routinely used in volcano monitoring. Sulfur isotopes provide a powerful tool for studying sources of sulfur, degassing processes and pre-eruptive volatile contents of magmas. The proposed study is a quantitative, robustly constrained evaluation of sulfur isotope fractionation during volcanic degassing that will allow assessment of currently employed isotope fractionation models and fractionation factors. The study will measure S abundances in gas and melt, speciation of S in the melt and gas phases, isotope compositions of all S species, and use measured constraints on degassing conditions such as temperature and the fugacity of oxygen (fO2). The study will also assess disequilibrium fractionation during degassing. All data will be obtained from the consistently degassing basaltic lava lake of Erta Ale, Ethiopia. Erta Ale is ideal for this study because it has a relatively reduced magma (fO2 ~ QFM), high, consistent SO2 flux and high S content in the gases. Erta Ale provides a reduced end-member for terrestrial S degassing. The results from this study will be compared with an oxidizing end-member (QFM +1.6 and high S flux) represented by volcano Masaya that is located in a subduction zone setting.
This research project had the objective to investigate the isotopic fractionation of sulfur during the degassing of basaltic magma. Understanding this isotopic fractionation is important when we attempt to assess how sulfur is emitted from the magma, through volcanoes to the atmosphere. In particular, knowing the isotope fractionation allows scientists to measure sulfur in erupted rocks and then obtain better estimates of how much sulfur has degassed from this magma. Such estimates are key when we try to evaluate the climatic effects of volcanic eruptions. Our project focused on the longest-lived lava lake on Earth, Erta Ale volcano, Ethiopia, where we were able to obtain samples of the lava, the sulfur in the volcanic plume as it was discharging from the lava lake as well as samples from a 1060C volcanic vent. The combination of these different sulfur samples and detailed analytical work in the laboratory showed that sulfur isotopes are fractionated due to equilibrium and kinetic processes, depending on magma composition. Therefore, our work was the first to show in a natural system that kinetic isotope fractionation needs to be taken into account. The broader impacts of this work include training of local scientists in collection of gas samples and measurements of SO2 emissions from volcanoes, the training of a Ph.D. student in a large number of field and analytical techniques. This includes work on mass spectrometers, a synchrotron, electron probe and ion probe. The data and images of this work are regularly used in Geology and Volcanology classes at the University of New Mexico. In particular introduction to Geology students are informed about the processes of volcanic eruptions, lava movement and magma degassing using images and data obtained from this project. Broader impacts also include the significance of our work for the evaluation of the climatic effects of sulfur degassing from volcanoes as well as better evaluation of the ultimate sources of sulfur which is key to understanding the global sulfur cycle.
