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During recent decades, dozens of commercial and military jets have inadvertently flown through volcanic ash clouds downwind from eruptions. These encounters have caused up to tens of millions of dollars (US) in damage to each jet; a few nearly crashed when ceramitized deposits of ingested ash caused engines to fail. In order to avoid such encounters, the International Civil Aviation Organization (ICAO) has established Volcano Ash Advisory Centers (VAACs) throughout the world to detect eruptions using satellite imagery and to notify aircraft. VAACs also predict the paths of ash clouds using atmospheric transport models, using information on volcanic plume height, the mass rate of tephra entering the atmosphere, the vertical distribution of tephra, eruption duration, and grain size distribution as input parameters. In some cases, these" source parameters" must be estimated during an ongoing eruption with few or …