LAVA DISCHARGE RATE ESTIMATES FROM THERMAL INFRARED SATELLITE DATA FOR PACAYA VOLCANO, GUATEMALA: IMPLICATIONS FOR TIME-AVERAGED ERUPTION PROCESSES AND HAZARDS

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 the 248 lava flows that occurred during this time. In this investigation, time-averaged discharge rates (TADR) were estimated for a subset of the flows listed in the database 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 unique database provides an excellent opportunity to test the applicability of the satellite-based method at Pacaya, where results can be compared with reliable ground-based measurements. In addition, this study assesses whether measurements from two sensors of differing temporal and spatial resolutions could be used simultaneously: MODIS (one image every 6 hours, 1-km pixels) and GOES (one image every 15 minutes, 4-km pixels). A total of 2403 MODIS and 2642 GOES images were analyzed, and 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 GOES data. The small, sub-resolution flows typical of Pacaya may have surpassed the limits of GOES data for this particular method. 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. It was suggested that the lower TADR experienced during longer “bleeding” of the conduit approximate the magma supply rate to the shallow system. Higher TADR eruptions may represent release of volumes collected during phases of non-eruptive degassing.