Lava discharge rate estimates from thermal infrared satellite data for Pacaya volcano, Guatemala: Implications for time-averaged eruption processes

The Pacaya volcanic complex has been producing lava flows nearly continuously since 1961. Matías (2009) compiled a detailed database including information such as length, surface area, volume, duration, and effusion rates for each of the 248 lava flows that occurred during this time. In this investigation, time-averaged discharge rates (TADR) were estimated for a subset of lava flows using a satellite-based method initially applied to infrared satellite data for Etna by Harris et al. (1997). Satellite-based estimates potentially provide a quicker, safer, and less expensive alternative to ground-based measurements and are therefore valuable for hazard mitigation. The excellent record of recent activity at Pacaya provides a unique opportunity to calibrate results from the satellite-based method by comparing them with reliable ground-based measurements. Imagery from two sensors of differing temporal and spatial resolutions were analyzed in order to produce a comprehensive dataset: MODIS (one image every 6 hours, 1-km pixels) and GOES (one image every 15 minutes, 4-km pixels). As of August 2011, 2403 MODIS and 2642 GOES images have been analyzed. Due to the relatively low intensity of Pacaya's effusive activity, each image was searched manually for volcanic "hot spots". It was found that MODIS data allowed better estimations of TADR than did GOES data. We suggested that the very small, sub-resolution flows typical of Pacaya may have surpassed the limits of low-resolution GOES imagery for this particular application. TADR derived from MODIS data were used to describe and parameterize eruptive cycles, as well as to explore conduit models. A pattern was found over the past two decades of short high-TADR periods followed by longer low-TADR periods. We suggested that the low TADR experienced during longer "bleeding" of the conduit may approximate the magma supply rate to the shallow system, while high TADR eruptions may represent the release of volumes collected during phases of non-eruptive degassing. The supply rate was estimated as approximately 6777 m³/day. Since Pacaya is a continuously degassing, open-vent volcano, the supply rate to the conduit can also be estimated via sulfur dioxide gas measurements. Developing results will be discussed.