MORPHOLOGY AND SEDIMENTATION IN CARIBBEAN MONTANE STREAMS - EXAMPLES FROM JAMAICA AND PUERTO-RICO

This paper presents a summary description of the morphology, sedimenta tion, and behaviour of the montane streams of eastern Jamaica and east ern Puerto Rico. The area is located within a 200 km wide seismically active zone of Neogene left-lateral strike-slip deformation which defi nes the plate boundary between the Caribbean and North American Plates . Tropical storms, occasionally strengthening up to hurricane force, a ffect the region periodically. This is an area of steep, mass-movement -scarred hillslopes which supply a large amount of coarse sediment to the rivers. From the description presented, we have constructed a mode l for the rivers of this region controlled by both neotectonics and pe riodic large floods. The drainage density is low with a near-rectangul ar stream network. The gradients are steep with boulder accumulations in the channels, their location at times related to the presence of la rge past landslides on hillslopes. Narrow, steep and confined channels occur in the mountains, but in wider sections and lower down near coa stal plains, flood depositional forms appear in coarse valley alluvium . Small-scale deviations from the general pattern occur locally, contr olled by variations in lithology, neotectonism, seasonality in flow, e tc. This model for Caribbean montane streams differs considerably from the standard descriptions of alluvial rivers for which a number of de tailed studies are available.