Abstract
Over the past 9,150 years, at least 9 flank collapses have been identified in the history of La Soufrière of Guadeloupe volcano. On account of the volcano’s current unrest, the possibility of such a flank collapse should not be dismissed in assessing hazards for future eruptive magmatic as well as non-magmatic scenarios. We combine morphological and geophysical data to identify seven unstable structures (volumes ranging from 1 × 106 m3 to 100 × 106 m3), including one that has a volume compatible with the last recorded flank collapse in 1530 CE. We model their dynamics and emplacement with the SHALTOP numerical model and a simple Coulomb friction law. The best-fit friction coefficient to reproduce the 1530 CE event is tan(7°) = 0.13, suggesting the transformation of the debris avalanche into a debris flow, which is confirmed by the texture of mapped deposits. Various friction angles are tested to investigate less water-rich and less mobile avalanches. The most densely populated areas of Saint-Claude and Basse-Terre, and an area of Gourbeyre south of the Palmiste ridge, are primarily exposed in the case of the more voluminous and mobile flank collapse scenarios considered. However, topography has a prominent role in controlling flow dynamics, with barrier effects and multiple channels. Classical mobility indicators, such as the Heim’s ratio, are thus not adequate for a comprehensive hazard analysis.
Highlights
The Guadeloupe archipelago is located in the northern part of the Lesser Antilles arc that resulted from subduction of the North and South American plates under the Caribbean plate
Three main rivers have their source in the vicinity of La Soufrière volcano: Le Galion and Rivière Noire flow south-west twoards the cities of Saint-Claude and Basse-terre, and the Rivière du Grand Carbet heads east
The 1530 CE debris avalanche volume was estimated at 80 ± 40 × 106 m3 7–9
Summary
The Guadeloupe archipelago is located in the northern part of the Lesser Antilles arc that resulted from subduction of the North and South American plates under the Caribbean plate. La Soufrière of Guadeloupe is an andesitic active volcano It belongs to the 0.445 Ma old Grande Découverte-La Soufrière volcanic complex[2,3] and is located about 2 km north of the town of Saint-Claude where about 10 000 people live (Fig. 1). To the south and south-west, old massive lava flows (Parnasse Plateau, Palmiste plateau) and eruptive centers (Morne Goyavier, La Citerne, Morne Graine Verte, Gros Fougas) partially protect inhabited areas. They are cut by numerous ravines, such as the Ravine de la Citerne and the Ravine Blanche. Near-field deformations, including inflation (3–7 mm/year) and flank basal spreading (7–10 mm/year), are recorded[17,18,19,20]
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