| Satellite data are used to study the explosive volcanic eruptions of El Chichon, Mt. Spurr, and Bezymianny volcanoes. The 1992 eruption of the Crater Peak vent of Mount Spurr, Alaska was investigated using Advanced Very High Resolution Radiometer (AVHRR) satellite data. Volcanic clouds generally have a negative AVHRR band 4 minus band 5 brightness temperature difference (BTD), while meteorological clouds generally have a positive BTD signal. Volcanic clouds imaged during and shortly after eruption are optically thick and can contain abundant water droplets and (or) ice, and these characteristics cause their spectral signal to closely resemble a meteorological cloud (e.g. positive BTD). As the volcanic cloud becomes translucent, the BTD signal changes, becoming negative first at the edge, and then throughout the entire cloud.;The 1982 eruption of El Chichon, Mexico was observed using AVHRR image data and the Total Ozone Mapping Spectrometer (TOMS). Comparisons are presented of satellite retrievals from the AVHRR sensor, which detects and estimates the mass of fine grained volcanic ash, and the TOMS sensor, which detects and estimates the mass of sulfur dioxide, for three days following the two large eruptions on April 4, 1982. Analysis of the satellite imagery and wind data show that the main mass of volcanic ash moved east and south, at an altitude at or near the tropo-pause, while the main mass of sulfur dioxide moved to the west in the stratosphere. It is likely that the separation of volcanic ash and sulfur dioxide observed in the imagery is the result of vertical segregation of the two components, caused by the sedimentation of ash, and the subsequent dispersal by winds of different directions and (or) velocities.;One of the primary public safety objectives of the Alaska Volcano Observatory (AVO) is to mitigate the hazard posed by volcanic ash clouds drifting into the busy North Pacific air traffic routes. A case study of the December 4, 1997 eruption of Bezymianny volcano, Russia, is used to illustrate how real-time remote sensing and hazard communication are used to mitigate the, threat of volcanic ash to aircraft. (Abstract shortened by UMI.)... |
