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3 - Volcanic ash fall hazard and risk
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- By S.F. Jenkins, University of Bristol, UK, T.M. Wilson, University of Canterbury, New Zealand, C. Magill, Macquarie University, Australia, V. Miller, Geoscience Australia, Australia, C. Stewart, Massey University, New Zealand, R. Blong, Aon Benfield, Australia, W. Marzocchi, Istituto Nazionale di Geofisica e Vulcanologia, Italy, M. Boulton, University of Bristol, UK, C. Bonadonna, University of Geneva, Switzerland, A. Costa, Istituto Nazionale di Geofisica e Vulcanologia, Italy
- Edited by Susan C. Loughlin, Steve Sparks, University of Bristol, Sarah K. Brown, University of Bristol, Susanna F. Jenkins, University of Bristol, Charlotte Vye-Brown
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- Book:
- Global Volcanic Hazards and Risk
- Published online:
- 05 August 2015
- Print publication:
- 24 July 2015, pp 173-222
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Summary
Executive summary
All explosive volcanic eruptions generate volcanic ash, fragments of rock that are produced when magma or vent material is explosively disintegrated. Volcanic ash is then convected upwards within the eruption column and carried downwind, falling out of suspension and potentially affecting communities across hundreds, or even thousands, of square kilometres. Ash is the most frequent, and often widespread, volcanic hazard and is produced by all explosive volcanic eruptions. Although ash falls rarely endanger human life directly, threats to public health and disruption to critical infrastructure services, aviation and primary production can lead to potentially substantial societal impacts and costs, even at thicknesses of only a few millimetres. Communities exposed to any magnitude of ash fall commonly report anxiety about the health impacts of inhaling or ingesting ash (as well as impacts to animals and property damage), which may lead to temporary socio-economic disruption (e.g. evacuation, school and business closures, cancellations). The impacts of any ash fall can therefore be experienced across large areas and can also be long-lived, both because eruptions can last weeks, months or even years and because ash may be remobilised and re-deposited by wind, traffic or human activities.
Given the potentially large geographic dispersal of volcanic ash, and the substantial impacts that even thin (a few mm in thickness) deposits can have for society, this chapter elaborates upon the ash component of the overviews provided in Chapters 1 and 2. We focus on the hazard and associated impacts of ash falls; however, the areas affected by volcanic ash are potentially much larger than those affected by ash falling to the ground, as fine particles can remain aloft for extended periods of time. For example, large portions of European airspace were closed for upto five weeks during the eruption of Eyjafjallajökull, Iceland, in 2010 because of airborne ash (with negligible associated ash falls outside of Iceland). The distance and area over which volcanic ash is dispersed is strongly controlled by wind conditions with distance and altitude from the vent, but also by the size, shape and density of the ash particles, and the style and magnitude of the eruption. These factors mean that ash falls are typically deposited in the direction of prevailing winds during the eruption and thin with distance. Forecasting ash dispersion and the deposition ‘footprint' is typically achieved through numerical simulation.
9 - Aspects of volcanic hazard assessment for the Bataan nuclear power plant, Luzon Peninsula, Philippines
- Edited by Charles B. Connor, University of South Florida, Neil A. Chapman, Laura J. Connor, University of South Florida
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- Book:
- Volcanic and Tectonic Hazard Assessment for Nuclear Facilities
- Published online:
- 27 May 2010
- Print publication:
- 27 August 2009, pp 229-256
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Summary
How would the eruption of a volcano affect a nearby nuclear power plant (NPP)? Specifically, would the products of a volcanic eruption impact the operation of an NPP located near an erupting volcano? The answer to this question begins with an assessment of the geological phenomena that result from volcanic eruptions. These phenomena are diverse, and include tephra fallout, pyroclastic flows and lahars, among others (Connor et al., Chapter 3, this volume). The effects of these phenomena depend on a host of factors, such as the proximity of the volcano to the NPP, the size and character of the eruption, wind direction and topography around the volcano.
The complexity and uncertainty associated with these phenomena suggest that their potential impacts be assessed probabilistically. One important aspect of probabilistic assessment involves forecasting the timing of eruptions. When will the next eruption occur? Or, phrased another way, how much time must elapse before a volcano no longer has a credible potential for future eruptions? This question is not easily resolved, as volcanoes may go thousands of years, or even tens of thousands of years without erupting. A second aspect of volcanic hazard assessment is estimation of the effects of volcanic eruptions, once they occur. Which areas might be inundated by lahars, or experience tephra fallout? As eruption magnitudes and their effects vary widely, this question must also be answered probabilistically. Admittedly, assessment of the timing and consequences of potential eruptions is a daunting task, requiring site-specific data, a refined understanding of volcanic processes and computational tools to actually estimate probabilities.