Multiple widespread landslides during the long-term evolution of a volcanic island: Insights from high-resolution seismic data, Montserrat, Lesser Antilles

Abstract : New high‐resolution multichannel seismic data (GWADASEIS‐2009 and JC45/46‐2010 cruises; 72 and 60 channels, respectively) combined with previous data (AGUADOMAR‐1999 and CARAVAL‐ 2002; 6 and 24 channels, respectively) allow a detailed investigation of mass‐wasting processes around the volcanic island of Montserrat in the Lesser Antilles. Seven submarine deposits have sources on the flanks of Montserrat, while three are related to the nearby Kahouanne submarine volcanoes. The most voluminous deposit (∼20 km 3) within the Bouillante‐Montserrat half‐graben has not been described previously and is probably related to a flank instability of the Centre Hills Volcano on Montserrat, while other events are related to the younger South Soufrière Hills‐Soufrière Hills volcanic complex. All deposits are located to the south or southeast of the island in an area delimited by faults of the Bouillante‐Montserrat half‐graben. They cover a large part of the southeast quarter of the surrounding seafloor (∼520 km 2), with a total volume of ∼40 km 3. Our observations suggest that the Bouillante‐Montserrat half‐graben exerts a control on the extent and propagation of the most voluminous deposits. We propose an interpretation for mass‐wasting processes around Montserrat similar to what has happened for the southern islands of the Lesser Antilles.