Volcanic ash. Hazard observation / Вулканический пепел. Наблюдение за опасностями

Airborne volcanic ash presents a well-publicized risk to aviation, health, and agriculture; for this reason, an important goal of volcano science relates to volcanic ash, including both its transport through the air during volcanic crises and its ultimate distribution over the ground and sea. The state of the science has advanced rapidly in the years since 2010, in large part because of interest generated by the high economic cost of the Eyjafjallajo¨kull eruption in Iceland in that year and the disruption it caused to aviation and aviation-dependent industries. Specifically, the eruption prompted a rapid change in the management of risk to aviation from volcanic ash clouds, precipitated by the use of safety thresholds for flight. Since that eruption, there has been a drive to improve volcanic ash detection and forecasting techniques (Watson, 2015) that allow Volcanic Ash Advisory Centers (VAACs) to issue the most relevant advice to aviation authorities. These management needs have highlighted the extent to which complementary expertise from different fields needs to be combined, both to reduce duplication of effort and to advance ash studies in all fields.
Here, we aim to advance volcanic ash studies by providing an overview of current understanding and methods used for observing and monitoring ash, both while it is in the air and once it is on the ground. We start with a review of volcanic ash itself: where it has come from, and what governs its physical and chemical properties during transport through the atmosphere and deposition on the ground (Part 2). We then review state-of-the-art techniques for data collection, interpretation, and modeling from the perspectives of ash deposition on the ground
(Part 3) and in situ ash sampling in the air (Part 4), followed by remote sensing from ground-based (Part 5) and satellite-based (Part 6) platforms. We conclude by summarizing the strengths and limitations of all approaches, and by highlighting the most pressing knowledge gaps in volcanic ash studies. Surprisingly, there are only a handful of eruptions for which ash deposition is sufficiently well characterized to test ways of correlating ash deposits on the ground with estimates of ash in the air. For this reason, these eruptionsdof Mount St. Helens, USA, in 1980; of Mount Spurr, USA, in 1992; and of Eyjafjallajo¨kull, Iceland, in 2010dform a common basis for study and for tuning models and algorithms. The strength of this approach is that multiple approaches are brought to bear on the same eruptions; the danger, however, is that tuning to a few events could reduce flexibility in our response to the next ash crisis. <...>