CORRELATING VOLCANIC SO2 EMISSION-RATES, SEISMICITY, AND ERUPTIVE PROCESSES

Volcanic emissions of sulfur dioxide (SO₂) were first observed and recorded in the late 1960’s, and have since been used as a valuable tool in tracking changes in volcanic activity. This data review compares correlations between SO₂ emission-rates, seismicity and eruptive processes of the active volcanoes Kilauea (USA), Mount Etna (Italy), Mount St. Helens (USA), Popocatépetl (Mexico), Masaya (Nicaragua), Soufrière Hills (Montserrat), Galeras (Colombia), and Karymsky (Kamchatka, Russia). This review combines published data and results, from observatories and institutions around the world, in order to examine the eruptive styles of these volcanoes and their relationship to trends of eruptive processes, precursory and syn-eruptive seismicity and SO₂ emission-rates. Publications and data sets dating back from 1979 and through to the present were analyzed and classified to both quantitatively and qualitatively reveal correlations between published findings of the volcanoes under investigation.

A variety of SO₂ emission-rate measurement systems were used at each of the sites of volcanic activity. The COSPEC and other miniature UV-spectrometer systems which used the DOAS method for analyzing spectral data were utilized based on the frequency of eruptive activity and accessibility to the volcanic plume. Preliminary results have shown that SO₂ emission-rates positively correlate with seismic activity, before, during, and after eruptive episodes. This can be seen in cases such as those of the 1991-1993 eruptions of Galeras volcano (Colombia) that reveal the long-term decreases in SO₂ flux associated with long-period seismicity. Other positive correlations between volcanic processes, such as ash blasts and increased lava extrusion rates, and SO₂ emission-rates have been observed at several of the volcanoes examined in this review. Published interpretations as to the cause of the observed correlations between SO₂ flux and seismic/volcanic activity are included in this presentation.