SEISMO-THERMAL ZONES AND A REASSESSMENT OF THE VOLCANIC HAZARD ON DOMINICA, LESSER ANTILLES

The island of Dominica, located in the center of the Lesser Antilles island arc, is unique in that it is interpreted to be the site of nine potentially active volcanoes. In contrast, on the other islands of the Active Arc of the Lesser Antilles only one volcano on each island is currently thought of as potentially active. Since the last magmatic eruption on Dominica around 450 years B.P., volcanic-related activity has been restricted to island-wide geothermal phenomena, and swarms of shallow earthquakes (at least 17 since Europeans settled the island in 1715). Using these associations, six seismo-thermal zones which do not always correspond to individual volcanoes have been identified throughout the island. Evaluation of these zones indicate that four zones on the island appear to be most likely to experience volcanic activity in the future. These zones include seismo-thermal zone 1 corresponding to the Morne aux Diables stratovolcano in the north; seismo-thermal zone 3 comprising the geothermal field in and around Prince Rupert Bay on the north-east coast, off shore from the second largest town of Portsmouth,, seismo-thermal zone 5 corresponding to the Wotten Waven caldera and the Valley of Desolation (the site of the two historic phreatic eruptions) located inland of the island’s capital and main population center of Roseau, and seismo-thermal zone 6 made up of the centers of Morne Anglais and Morne Plat Pays in the south. Although this reinterpretation of the volcanic hazard on Dominica reduces the number of known volcanoes regarded as potentially active from nine to four, the hazards and their associated risks presented by these volcanoes (Morne aux Diables, Wotten Waven caldera, Morne Anglais and Morne Plat Pays) as well as the Prince Rupert Bay geothermal field, are formidable and any future crises at these centers are likely to be beyond the infrastructural and financial resources of Dominica.