| A handheld thermal video camera, or FLIR (Forward Looking Infrared Radiometer), was used to understand the dynamics of strombolian eruptions. Images (at up to 30 frames per second) were collected for 344 eruptive events occurring between 2001 and 2004 at Stromboli volcano, Italy. Two major eruption styles were observed: Type 1, which are dominated by ballistic particles and Type 2, which are dominated by an optically-thick ash plume, with (Type 2a) or without (Type 2b) additional ballistic particles. Eruption styles (Type 1 vs. 2) were generally maintained on a scale of days to weeks for a given vent. Type 1 eruptions indicated a clear magma-air interface, while Type 2 eruptions were likely caused by loose backfill sitting atop the magma column. Type 2a and 2b behaviors are shown to be a function of bubble overpressure and backfill muffling. These results support a broadening of the current paradigm for strombolian behavior.; Strombolian ash plumes (i.e., Type 2) were analyzed in detail, with fine timescale tracking of rise rates, dimensions and temperatures. Type 2a eruptions exhibited gas thrust velocities (>15 m s-1), while Type 2b eruptions rose at buoyant velocities only (<15 m s-1). Velocity trends produced varying plume morphologies which in turn controlled air entrainment rates, as shown by measurements of spreading rates. Plume temperatures began between 300 and 600°C, and generally dropped to <150°C in the first 100 m of rise. Determining plume opacity is imperative in using FLIR-derived plume temperatures. Plume temperatures varied on a daily basis, likely a function of the amount of accidental ash available to entrain. Using a heat conservation approach, explicit mass estimates were made. Due to a lack of knowledge of gas mass fraction, however, the mass results had uncertainties on the order of 60%.; Integrating these ideas and models, an automated approach is presented to process Strombolian FLIR data and determine eruption style, ejecta mass and collimation. In some cases a spot radiometer, instead of the more expensive FLIR, can be used garner ejecta mass. The automated routine could prove useful in identifying anomalous behavior that might presage hazardous eruptive phases. |
