Basse-Terre Island is part of the West-Indian arc. It was formed when the South American plate subducted under the Carribean plate, a process which is still ongoing.
Basse-Terre Island is primarily made up of andesitic rocks, which are particularly susceptible to chemical weathering. The dates of emplacement of the lavas sampled at the island's surface as determined by Samper et al. decrease from the north (2.8 Ma) to the south (0 Ma), with some periods demonstrating particularly high volcanic activity. Towards the north, the surface is less steep and the soil is thicker.
Basse-Terre Island is mostly covered by a dense primary forest, most of which is protected by the Guadeloupe National Park (PNG, Parc National de Guadeloupe), while the central part of the massif is covered by a hygrophilous forest .
It should also be noted that the acid responsible for mineral degradation is generally carbon dioxide, which is released during the decomposition of soil organic matter. Another source of CO2 in Guadeloupe can be traced in several of its drainage basins. This deep-source CO2 arises from slow volcanic outgassing and is released through the island's fault lines, including those that are not in immediate proximity to the Soufrière Massif. This process provides a useful model for gas escaping from future CO2 storage layers in geological condition. Basse-Terre Island has an insular tropical climate, with heavy annual precipitations which vary between 10 metres of water per year at the summit of La Soufrière, and 1.2 metres per year in less than ten hours on the driest areas of the lee shore (Western). Every year the wet season, which lasts from July to December, brings tropical depressions, which can develop into storms and cyclones. These phenomena trigger a rapid increase in the river flow rates, which respond to meteorological changes within a few hours. It is not uncommon to see 100 mm of water fall on the La Soufrière mountain range in less than ten hours; this intense precipitation causes landslides, flooding, and sudden exportation of sediments. Flash floods recur on an annual basis in the rivers of Guadeloupe, whereas they recur once every hundred years in temperate areas. The bulk of erosion occurs during these discrete periods, which are difficult to sample. Provided suitable measuring techniques are developed, the geological conditions on Guadeloupe allow scientists to chart how extreme climate phenomena affect land surface dynamics.
The combination of these parameters makes Guadeloupe an ideal site for studying erosion and weathering. Together with the ageing of the north-facing relief, the climate and geology of the island firstly allow scientists to study soil placement and the morphological development of the drainage basins and, secondly, to examine what impact they have on the chemistry of alterites, the residence time of materials, and even physical denudation and river morphology. The unique conditions on Basse-Terre Island also allow scientists to analyze how precipitations change river chemistry, weathering, and even the dynamics of sediment transport in rivers in an environment shaped by tectonic movement and volcanic activity.
1 - Rousteau, A., 1996. Structures, flores, dynamiques: réponses des forêts pluviales des Petites Antilles aux milieux montagnards. In: Guillaumet, J.L., Belin, M., Puig, H. (Eds.), Phytogéographie tropicale: réalités et perspectives. ORSTOM, Paris.
2 - Samper, A., Quidelleur X., Mollex D. and Lahitte P. Timing of effusive volcanism and collapse events within an oceanic arc island. Earth. Planet. Sci. Letters. 2006
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