The Morne Watt centre is dominated by Pelean domes surrounded by an apron of block and ash flow deposits. Watt Mountain is composed of a central complex containing at least three coalesced domes within an arcuate crater. A single parasitic Pelean dome also occupies the eastern flank of the volcano. Wills (1974) reports andesitic lavas from Watt Mountain underlying pyroclastic deposits in the Perdu Temp and Pichelin rivers in the east, and Demange et al. (1985) describe the western foundations of the volcano as comprising massive andesite lavas suggesting that the initial history of this volcano was more effusive than explosive. The volcano's eastern flanks are smooth and lack deep erosional gullies. This suggests that the flanks of Watt Mountain are covered by relatively young pyroclastic deposits, with possible exposures found in the upper Jack river, where ignimbrites dated at 10,290 years B.P. have been described (Lindsay et al. 2005a). The presence of these ignimbrites indicates that Watt Mountain underwent a period of Plinian-style eruptions, in addition to its more common Pelean-style eruptions.

Smith A.L et al: Unpublished data.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.