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Timely detection and quantification of lava effusion rates are crucial for volcanic hazard mitigation during effusive eruptions. Satellite-based detection methods typically exploit the exceptional radiant heat fluxes associated with lava effusion, but effusive eruptions can also emit prodigious amounts of sulphur dioxide (SO2). Measuring the magnitude and temporal evolution of SO2 emissions provides an additional means for monitoring effusive eruptions, complementing thermal monitoring. Examples of effusive eruptions detected since 1978 using ultraviolet (UV) satellite measurements of SO2 emissions by the Total Ozone Mapping Spectrometer (TOMS), Ozone Monitoring Instrument (OMI) and Ozone Mapping and Profiler Suite (OMPS) are reviewed. During many effusive eruptions, trends in SO2 production mimic the classic waxing–waning pattern characteristic of such events that is also seen in thermal infrared (TIR) hotspot data, suggesting a qualitative link between SO2 emissions and lava effusion rates. An example of lava effusion rate calculation based on TOMS SO2 measurements is presented for the 1998 eruption of Cerro Azul (Galápagos Islands), for which detailed eruption observations and independent estimates of effusion rates are available. Combining TOMS-derived SO2 emission rates with estimates of sulphur content in Cerro Azul lavas yields lava effusion rates almost identical to independently derived values, demonstrating the utility of the technique.

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