Continuous Monitoring of Periodic Eruptive Cycles at Santiaguito Dome Complex, Guatemala

Recent activity at Santiaguito dome complex has been characterized by degassing, extrusion of dacite lava to feed block flows, as well as periodic small-scale eruptions of blocks and ash from the active El Caliente vent. Our objective was to study the behavior of the active vent and characterize the short-term periodic eruptions that take place. Three overlapping data sets have been collected from the top of Santa Maria looking down onto the active vent \2.5 km away within a cumulative observation time of 2.5 hours. Approximately 600 spectral curves were collected using the ASD field spectrometer, while continuous integrated temperature measurements were made using the Raytek radiometer. Both instruments have a 1° field of view. Digital video footage was also collected concurrent with other observations. We used Planck's Law and applied a two-component thermal model to the spectral curves to produce a time series revealing crust and crack temperatures, as well as the fractional area of the hot thermal component. Using the two temperature time-series, we can distinguish several different phases of dome activity: (1) individual exposures of hotter lava within data collection time period, (2) cooling of the recently extruded surface, and (3) disruption of that surface by events. Three individual exposures of hotter material can be observed from the temperature time series. The newly extruded surface shows extremely rapid initial cooling (8° /s) followed by a gently sloped cooling curve for 45 minutes before the next extrusion occurred. During one cooling phase, the surface can be characterized by a two-component model, a cooler crust with temperature range of 120 to 350° C, and hot cracks with temperatures of >700° C. During the explosive event, the fractional area of the hot component increased to nearly 90% with temperatures in excess of 800° C. Following the rapid initial cooling after the extrusion event, the dome behaved as a single component surface with temperatures ranging from 300-500° C. We postulate three scenarios could be partially responsible for these characteristic: (1) new cracks opening during the explosive events, exposing a hot core which cool rapidly upon exposure, (2) low energy stirring of the dome materials, exposing hotter sides of the blocks to the surface, or (3) disruption of the surface where there's enough energy to overturn blocks as well as physically ejecting materials into the air.