A SUMMARY OF SULFUR-DIOXIDE EMISSION RATE MEASUREMENTS FROM GUATEMALAN VOLCANOS

Measurements of the sulfur dioxide (SO2) emission rate from three Guat emalan volcanoes provide data which are consistent with theoretical an d laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measu red SO2 emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO2 emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO2 emission rate measurements are consi stent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recen t SO2 emission rate measurements support laboratory simulation studies of strombolian eruptions, these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions . Average SO2 emission rates over the last 20 years for Santiaguito, F uego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global sc ale, these three volcanoes account for 1% of the annual global volcani c output Of SO2. Santiaguito and Pacaya, together, emit 6% of the tota l annual SO2 emitted by continuously erupting volcanoes. Even though S O2 measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a usefu l baseline by which to judge future changes. A more complete record of SO2 emission rates from these volcanoes could lead to a better unders tanding of their eruption mechanisms and reduce the impact of their fu ture eruptions on Guatemalan society.