5th Swiss Geoscience Meeting, Geneva 2007
Assessing volcanic hazards: quantitative models of
tephra fall.
Costanza Bonadonna
Département de Minéralogie, Université de Genève, Rue de Maraîchaire 13, CH-1205
Genève
(Costanza.Bonadonna@terre.unige.ch)
Depending on their magnitude and location, volcanic eruptions have the
potential for becoming major social and economic disasters (e.g. Tambora,
Indonesia, 1815; Vesuvius, Italy, 79 AD; Montserrat, West Indies, 1995present). One of the modern challenges for the volcanology community is to
improve our understanding of volcanic processes in order to achieve successful
assessments and mitigation of volcanic hazards, which are traditionally based
on volcano monitoring and geological records. Geological records are crucial to
our understanding of eruptive activity and history of a volcano, but often they
are not comprehensive of the variation of volcanic processes and their effects
on the surrounding area. They are also typically biased towards the largest
events. Numerical modelling and probability analysis can be used to
complement direct observations and to explore a much wider range of possible
scenarios. As a result, numerical modelling and probabilistic analysis have
become increasingly important in hazard assessment of volcanic hazards (e.g.
(Barberi et al., 1990; Canuti et al., 2002; Heffter and Stunder, 1993; Hill et al.,
1998; Iverson et al., 1998; Searcy et al., 1998; Wadge et al., 1998; Wadge et
al., 1994)).
Assessments of hazards related to dispersion and accumulation of tephra fall
are a good example of the application of this modern approach and typically rely
on the critical combination of field data, numerical simulations and probability
analysis. Tephra is one of the main products of explosive eruptions and can be
transported in the atmosphere for long time and distance causing respiratory
problems to human and animals, serious damage to buildings and also affecting
several economical sectors such as aviation, agriculture and tourism. Hazard
assessments for tephra dispersal are typically based on the compilation of (i)
probability maps and (ii) hazard curves. Probability maps are compiled using
specific hazardous thresholds of tephra accumulation (e.g. damage to
vegetation, collapse of buildings and airport closure) and for specific activity
scenarios, e.g. One-Eruption Scenario, Eruption-Range Scenario, One-Wind
Scenario and Multiple-Eruption Scenario for the minimum and for the maximum
deposit. Probability maps based on a particular return period of tephra
accumulation can also be compiled and they generally account for the whole
history of a volcano. Hazard curves are more flexible as they are not based on
any hazardous thresholds or particular return period. All hazard assessments
strictly depend on the specific nature and history of a volcano and need to be
combined with thorough field investigations. Field investigations are crucial to (i)
the compilation of the activity scenarios, (ii) the calibration of the dispersal
models and (iii) the determination of the input parameters.
5th Swiss Geoscience Meeting, Geneva 2007
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