"Plate tectonics" -- for those interested in modern interpretations of the geology:

The Caribbean 'plate' is overriding the Atlantic 'plate', which is being 'subducted' down and providing materials which become part of the magma which fuels the Lesser Antillean volcanoes.

The locus of the edge of the Caribbean 'plate' is perhaps 50 miles east of Dominica, and the crumbling edges of both plates are responsible for the seismic activity so common off east Dominica and in Southern Dominica.

Dominica lies at the center of the Lesser Antilles Island arc, where the islands of the Active Arc are large and complex comprising many coalesced stratovolcanoes. The island has an area of 750 sq.km and a population of 74,000 including 3,000 Carib Indians. Whereas all the other volcanic islands of the Lesser Antilles have only one active volcano, Dominica has nine and yet there has been no major magmatic eruption since Columbus visited the island and as a result it has today the best and most extensively preserved tropical rainforests. The youngest dated volcanic deposits on the island are associated with the Morne Patates dome on the flanks of the large active Plat Pays Volcano that comprises the southwestern end of the island. This was a Pelean eruption (similar to the eruptions of Mt. Pelee on Martinique in 1902 and 1929) and radiocarbon ages from the block and ash deposits suggest it occurred about 500 year ago. In addition there have been two steam explosions (phreatic activity) in the Valley of Desolation in 1880 and 1997. Frequent seismic swarms and vigorous and widespread geothermal activity today characterize the island. In fact it is the most worrying of all the Caribbean volcanic areas and there is a general feeling that it (like Montserrat pre-1995) is long overdue for an eruption. What is of particular concern is that the capital Roseau and most of the islands infrastructure lie on a pyroclastic flow fan derived from the Wotten Waven caldera situated on the eastern outskirts of the capital.The pyroclastic deposits of the Roseau area abound with ignimbrites (pumiceous pyroclastic flows), surge and airfall deposits with radiocaron ages ranging from 38,000 to 1000 years B.P. Volcanologist Haraldur Sigurdsson as long ago as 1972 described one of the units which he called the Roseau ash and together with other workers traced its submarine extension. As a result of this work they concluded that about 38,000 years ago the island erupted around 56 cubic kilometers of pumiceous materials in what was described as the largest eruption in past 200,000 years in the Caribbean . Pyroclastic flows deposited about 30 cubic km on the Caribbean floor and the remainder was deposited on the Atlantic floor from AntiTrade Wind dispersal. More recent work suggests that there are several ignimbrite sheets separated by ancient soils and the deposits may have resulted from several eruptions. However all conclusions indicate that the capital Roseau is situated in one of the most hazardou s areas of the island. The structure of the island is interesting as north of Dominica the Lesser Antilles arc divides into two, with the active arc lying to the west in Basse Terre of Guadeloupe and the extinct Limestone Caribbee arc lying to the east in Marie Galante and Grande Terre of Guadeloupe . On Dominica , Miocene rocks (7-5.3 million years) of the Extinct Limestone Caribbees occupy the east or windward coast where deeply dissected volcanoes form rugged mountains. The main bulk of the island was built up by coalesced volcanoes during the Pliocene (4.0-2.0 million years). During the Pleistocene (<2 million years) a number of young volcanic centers have been building over the Pliocene rocks and are separated from them by an extensive saprolite-laterite soil horizon caused by a long period of tropical weathering that formed about 2 million years ago. The distinctive center of Morne aux Diables in the north and Plat Pays in the south have extended the area of the Miocene-Pliocene volcanic island. In the south central part of the island, in what was a large basaltic shield volcano, a central graben developed in the Pleistocene that measures 6km east-west by 12 km north-south and is bounded by conspicuous cliffs to the west and north.