Morne Trois Pitons (three peaks mountain) is a large volcanic structure occupying the northern part of the southern third of the island. Its summit is now occupied by three domes.

Demange et al. (1985) divide the eruptive history of Morne Trois Pitons into three stages.

1) An initial Pelean-style stratovolcano with summit domes. Deposits characteristic of this stage, which have not been dated, are exposed on the northern side of the Boeri river, where they lie on top of andesitic lava flows of Pliocene age, and on the west coast north of Roseau, best exposed in the area of Canefield.

2) These deposits are pumiceous and reflect a shift from Pelean to Plinian style activity. Ignimbrites from these Plinian eruptions cover an area of 62 km2 and are exposed in two fans, one extending northeast towards the valley of the Pagua River, and the other to the northwest where it reaches the coast at Layou village. At least three flow units are exposed at Layou, one of which gave a date of >40,000 years B.P.

3) This stage is characterized by a return to Pelean-style activity with the extrusion of the current complex of Pelean domes. Eruptions associated with these domes produced block and ash flow deposits that are dominantly intra-caldera,
although a few flows extend outside the caldera margins and form valley-fill deposits that reached both the east and west coasts. These block and ash
flows have yielded 14C ages of 17,240 (Wadge 1989) and 25,310 (Roobol et al. 1983) years B.P.

Credits:

• Smith A.L et al: Unpublished data.
• Lindsay, J.M; Smith, A.L; Roobol, M.J; & Stasiuk, M.V. 2005. Dominica. In: Lindsay, J.M., Robertson, R.E.A., Shepherd, J.B., & Ali, S. (eds) 2005. Volcanic Hazard Atlas of the Lesser Antilles - Seismic Research Unit, The University of the West Indies, Trinidad and Tobago, W.I, 1-48.