Geological history and potential hazards of the late-Pleistocene to Recent Plat Pays volcanic complex, Dominica, Lesser Antilles

Abstract

During 1998–2000, the island of Dominica in the Lesser Antilles experienced a major volcanic earthquake swarm spatially associated with volcanic centres in the south of the island. This swarm provided the motivation for a major re-assessment of geologic history and volcanic hazards in this region. This has led to a re-interpretation of the south-western-most corner of the island as a large volcanic complex, termed the Plat Pays volcanic complex, which has exhibited a wide range of past eruptive activity and which, in the Quaternary, experienced a major caldera collapse triggered by a voluminous pyroclastic eruption. Stratigraphy and new 14C age determinations reveal a complicated history of development. The earliest activity is represented by the formation of the Plat Pays stratovolcano and associated parasitic domes. A major explosive eruption ~ 39,000 years B.P. produced the Grand Bay ignimbrite and triggered a major caldera collapse of the summit and south-western flank of the Plat Pays stratovolcano. Following the major eruption, re-injection of Plat Pays magma resulted in the extrusion of approximately 12 lava domes both within and outside the resulting depression. Caldera collapse was followed by at least one catastrophic flank collapse, but it is unclear whether or not this was triggered by caldera formation. The only on-shore evidence of flank collapse is the breach of the caldera rim and truncation of post-caldera deposits emplaced on or near the caldera rim; we find no evidence of on-shore large-magnitude rock avalanche deposits within the stratigraphic framework of the Plat Pays volcanic complex. Frequent seismic swarms of volcanic earthquakes and vigorous geothermal activity indicate that south Dominica is still underlain by an active magma reservoir system. Our new geological observations, combined with an interpretation of recent seismic swarm activity, suggest that an eruption (probably dome-forming) from the Plat Pays volcanic complex is probable within the next 100 years.