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VOLCANOESWhat is a volcano?Volcanoes are vents or openings in the Earth's crust through which, hot, molten rock (called magma) and gases from the interior of the Earth are released. Sometimes, but not always, the solid parts pile up around the vent to form a volcanic mountain. Some volcanoes are literally slits or holes in the ground while others are broad mountains with gentle slopes. Volcanoes in the Eastern Caribbean are mainly steep-sided and roughly conical in shape. They consist of alternating layers of solid lava (magma that has reached the Earth's surface) and broken fragments of lava called pyroclastic rocks. Since they are layered, they are called stratovolcanoes. |
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Why are there volcanoes in the Eastern Caribbean?The Earth's crust is made up of slabs of material called plates which move relative to each other. The Eastern Caribbean islands lie on a plate boundary. The North American Plate, which is the denser of the two, sinks beneath the Caribbean Plate creating suitable conditions for magma to be produced. The magma then rises to the surface of the Earth where it may erupt to form a volcano. This process is called subduction and this is how the volcanic islands of the Eastern Caribbean were formed. The diagram below demonstrates the subduction process. |
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There are 19 'live' (likely to erupt again) volcanoes in the Eastern Caribbean. Every island from Grenada to Saba is subject to the direct threat of volcanic eruptions (see map below). Islands such as Grenada, St. Vincent, St. Lucia, Martinique, Dominica, Guadeloupe, Montserrat, Nevis, St. Kitts, St. Eustatius and Saba have 'live' volcanic centres, while other islands such as Anguilla, Antigua, Barbuda, Barbados, British Virgin Islands, most of the Grenadines and Trinidad & Tobago (which are not volcanic) are close to volcanic islands and are, therefore, subject to volcanic hazards such as severe ash fall and volcanically-generated tsunamis. |
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Map of 'live' volcanoes in the Eastern Caribbean |
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Volcanic Activity in the Eastern CaribbeanWhile hurricanes are much more common in the Eastern Caribbean no hurricane has ever completely destroyed the capital of an Eastern Caribbean island (that is to say, made it completely uninhabitable) while volcanic eruptions have done so twice:
Additionally, while property destruction levels from severe hurricanes generally range from 10-25%, property destruction levels (and by extension, casualties) in the Eastern Caribbean caused by volcanic eruptions approach 100% in the most severely affected areas. Thus, the only appropriate action that can be taken to prevent this is a total evacuation of the areas likely to be affected. For this reason, public education and awareness in advance is crucial to successful disaster preparedness and mitigation programmes in that it equips the public with the necessary information to be able to make informed decisions and to facilitate (rather than obstruct) disaster response action in the event of a crisis. In assessing the threat posed by volcanoes to Eastern Caribbean countries, it is useful to review data on actual volcanic disasters over the past 300 years (see tables below). Keep in mind that there have been at least 15 other eruptions that have not resulted in large numbers of deaths or destroyed enough property to be ranked as disasters. |
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Actual volcanic disasters in the Eastern Caribbean over the past 300 years
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Volcanic eruptions and earthquakes share the common feature that they happen fairly infrequently but when they do happen the consequences can be devastating. By unfortunate coincidence the mean interval between such disasters is roughly comparable with one human lifetime so that the memory of the previous event would have just about faded from public consciousness when the next one occurs. Maintaining public preparedness for geologic disasters through the long, quiescent periods, therefore, presents a significant challenge. |
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