| Until recently, limitations in obtaining continuous, high-temporal resolution sulfur dioxide (SO2) emission rate data have hampered efforts to understand shallow processes within volcanic systems. Also, most gas measurements are either not representative of bulk composition (filter packs, traps, etc.) or, taken too far downwind (remote sensing techniques), where the atmosphere acts as a chemical and dynamic contaminator. The first of these limitations is being overcome in the form of new equipment with better temporal resolution and near real-time analysis. In order to get a better understanding of the timing of these processes, this study has taken advantage of this new technology, as well as innovative methodologies to produce continuous, high temporal resolution data. Observations of gas at the vent (or within a few seconds of release) are, in this context, most desirable. Here we present new techniques for observations of at-vent emissions, eliminating these potential problems and showing the timing of such processes as system re-sealing and pressurization. The primary goal of this dissertation can be stated thus:; How can we make measurements more robust and pertinent (primarily in a temporal context) to short-term changes in volcanic gas emission rates that can be used to investigate rapid (seconds-minutes) dynamical processes?; Several field experiments were undertaken in order to reach this goal. Thermal infrared radiometers were used at Masaya volcano, Nicaragua, to determine dilution of volcanic thermals (0.18 in 2002 and 0.22 in 2003) and the details of a new technique for estimating emitted gas fluxes are described. A new mathematic framework for estimating dilution independent of height above the vent is developed and presented for the first time. Frequency, amplitude, duration, diameter, velocity and volumes are estimated from the radiometer data. The volumes are used with previous gas ratio data to show reasonable agreement with independently acquired SO2 flux data. Also, another method of measuring SO2 gas fluxes using a miniature ultra-violet spectrometer through a static field of view is presented. This provides unprecedented temporal resolution on the order of one measurement per second. First-light data are presented for Santiaguito, Guatemala which provide vent detection, duration, and SO2 flux. Finally, this spectrometer method was used, in conjunction with thermal and seismic data, to provide a unique perspective of the shallow dynamic processes that are occurring at Santiaguito. Throughout, seismic signals were the initial indicators of activity, with a typical precursor of 5-10 seconds. This is attributed to the build up of gas and the subsequent failure of the dome material (with its associated seismic signal) that creates openings in the dome fractures. These openings, in turn allow the release of hot gases, indicated as spikes in the thermal and gas data, and the sharp onset of the explosion in the seismic data. A noticeable and significant decrease in gas emissions prior to explosions is shown to be attributed to a re-sealing of the dome fractures. However, an average amount of time needed to rebuild the pressure within the dome to create an explosion could not be established. |
