Geomorphological evolution of Montserrat (West Indies): importance of flank collapse and erosional processes

Analysis of topography and new swath bathymetry as well as geophysical data provides information about aerial and submarine morphological features and mass transfer processes on Montserrat. The island has a characteristic shallow (<100 m) submarine shelf, interpreted as having been formed through erosion with a depth controlled by glacio-eustatic sea-level variation. Several debris avalanche deposits are identified on the lower submarine flanks of Soufriere Hills volcano, and there is evidence of lateral collapses at the older volcanic centres. The morphological evolution of Montserrat is interpreted in terms of three stages. The first stage comprises submarine growth. The second stage, subaerial growth, is represented by the active South Soufriere Hills-Soufriere Hills volcanic centre. During the current eruption of Soufriere Hills volcano (19952002) more than half of the lava erupted was transported into the sea. Flank collapses occurred several times during this stage, such as the English's Crater event (c. 4000 years ago) or the Boxing Day event during the current eruption (26 December 1997). Montserrat's older volcanic centres, the Centre Hills and Silver Hills, illustrate the third stage of evolution, extinction and erosion. Magma production, long-term erosion and total sedimentation rates on Montserrat have been estimated as 0.17 km(3) ka(-1), 0.0125 km(3) ka(-1) and 0.11 km(3) ka(-1) (i.e. 1.1 cm ka(-1)), respectively.