CHARACTERISTICS AND MODELS OF CYCLIC ERUPTIVE ACTIVITY AT FUEGO VOLCANO, GUATEMALA (2005-2007) DERIVED FROM VISUAL OBSERVATIONS AND SEISMIC, ACOUSTIC AND THERMAL MEASUREMENTS

Fuego volcano, Guatemala is a high (3800m) stratovolcano that erupts gas-rich, high-Al basalt, often explosively. Because the volcano towers above a population of several tens of thousands of people, predicable patterns in its activity might have hazard mitigation implications. Fuego has been characterized by open vent conditions for much of the past ~75 years, but this activity has not been systematically observed or recorded until now. We conducted two years (2005-2007) of daily visual observations from a local observatory ~7km SW of the summit through the Peace Corps Masters International (PCMI) program at MTU. Activity included lava flows, explosions, degassing and paroxysmal eruptions.

We compared observed changes in active lava flow lengths to radiant heat output from MODIS to validate our observations. MODVOLC alerts from MODIS correlate well with observed changes in eruptive behavior, particularly abrupt changes from passive lava effusion to paroxysmal eruptions. A 1 Hz short-period seismometer and two low-frequency microphones recorded a rich variety of volcanic events during six months of 2007. Persistent tremor (1-3 Hz) dominated the seismicity, allowing a comparison of seismicity, thermal output, and observed activity during the final six months of the study. The data show a remarkable correlation that allowed us to identify a pattern of repeating eruptive behavior: 1) passive lava effusion and subordinate strombolian explosions coupled with low-level tremor, followed by 2) increased tremor amplitude leading to paroxysmal eruptions that produced sustained eruptive columns, long, rapidly emplaced lava flows, and block and ash flows, and finally 3) periods of discrete degassing explosions with no lava effusion and low-level tremor. This sequence of activity was observed five times during the duration of the study, and two complete cycles were recorded with the seismo-acoustic station. Explosion characteristics varied depending on which period of activity the volcano was in and this is reflected in relative energy partitioning between seismic and acoustic signals. Our results demonstrate that visual observations and ground-and satellite-based remote sensing can inexpensively track changes in volcanic activity at densely populated volcanoes in remote regions of underdeveloped countries.