I fenomeni vulcanici - Sei

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Risk Assessment: Predicting Volcanic Eruptions
Table 1 summarizes the major known volcanic disasters since
AD 1500. The potential for such disasters in the future makes a
volcanic eruption one of the greatest of geologic hazards. It
also makes risk assessment and prediction of volcanic eruptions
an important part of modern science.
Approximately 1,300 active volcanoes are recognized globally,
and 5,564 eruptions have occurred in the past 10,000 years.
These figures do not include the numerous submarine volcanoes
of the Mid-Oceanic Ridge system. Many volcanoes have
erupted recently, and we are certain that others will erupt soon.
How can geologists predict an eruption and reduce the risk of
a volcanic disaster?
Regional Prediction
Volcanoes concentrate near subduction zones, spreading centers,
and hot spots over mantle plumes but are rare in other
places. Therefore, the first step in assessing the volcanic hazard
of an area is to understand its tectonic environment. Western
Washington and Oregon are near a subduction zone and in a
region likely to experience future volcanic activity. Kansas and
Nebraska are not.
Furthermore, the potential violence of a volcanic eruption is
related to geologic environment of the volcano. If an active volcano
lies on continental crust, the eruptions may be violent because
granitic magma may form. In contrast, if the region lies
on oceanic crust, the eruptions may be gentle because basaltic
volcanism is more likely. Violent eruptions are likely in Western
Washington and Oregon, but less so on Hawaii or Iceland 1 .
Table 1 Some notable volcanic disasters since the year ad 1500 involving 4,000 or more fatalities
Hazard: a danger or risk
Assessment: evaluation, estimation
Likely: probable or expected
6 I fenomeni vulcanici
Risk assessment is based both on frequency of past eruptions and
on potential violence. However, regional prediction only estimates
probabilities and cannot be used to determine when a particular
volcano will erupt or the intensity of a particular eruption.
1 Katla is a large volcano in Southern Iceland. It is very active; twenty eruptions
have been documented between 930 and 1918, but its eruptions are not violent.
Katla has been showing signs of unrest since 1999, and geologists have concerns
that it might erupt in the near future.
Year Country Volcano Number of Death
1586 Indonesia Kelut 10,000
1631 Italy Vesuvius 6,000
1669 Italy Etna 10,000
1783 Iceland Lakagigar 9,350
1792 Japan Unzen 15,000
1816 Indonesia Tambora 92,000
1883 Indonesia Krakatoa 4,000
1902 Martinique Pelée 40,000
1902 Guatemala Santa Maria 6,000
1919 Indonesia Kelut 5,000
1985 Colombia Nevado del Ruiz 23,000
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