Yesterday MVO staffmembers Thomas Christopher and Pyiko Williams reinstalled a Multisensor Gas Analyzer System (MultiGAS), which measures the absolute ratios of CO2, H2O, H2S, and SO2.MVO’s MultiGAS has been out of commission since May 12 when one of its sensors failed and has until now been undergoing repair in Italy.
Having this instrument once again in operation is an important and exciting step for the monitoring of Soufriere Hills volcano. One reason is that where most of MVO’s gas monitoring techniques measure the amount of only one type of gas (species) at a time, MultiGAS measures the absolute ratios of four different gas species. Other gas monitoring techniques for multiple species require a substantial amount of time for analysis in a laboratory. Because MultiGAS analyzes data itself and sends it back to MVO, we can know the relative amounts of gases can occur more quickly. To get this chemical information, the system must be inside the actual volcanic gas plume where it routinely gathers and analyzes gas samples. The system was installed to the west of the volcano (where the plume usually goes) at Upper Spring Estate on the western flank of Chance’s Peak. MultiGAS collects data for 45 minutes, purges the system for 15 minutes, shuts down, and then begins again after another 4 hours.
Changes in the amount of gases relative to one another might have important implications for the monitoring of the volcano. At other volcanoes, such as Stromboli in Italy, an increase in the amount of CO2 has been seen before eruptions. It is not yet known whether Soufriere Hills Volcano will behave in the same way, but continued monitoring and analysis might tell us if CO2 abundance is an important indicator of possible future activity. Additionally, knowing the relative amount of SO2 and H2S might provide information about the behaviour of the volcano. Chemical conditions of the magma, such as redox conditions, control the relative amounts of SO2 and H2S that can form. Measuring the relative amounts of these two gases at the volcano’s surface might then provide information about what is going on with the magma beneath the volcano’s surface.