Transitional Basalts and Eruptive Dynamisms around Nkoumelap Locality (West of the Bamoun Plateau, Cameroon Volcanic Line): Petrography and Volcanic Risks’ Evaluation

摘要

Diverse eruptive dynamisms have occurred in the west side of the Bamoun plateau, producing ashes, scoria, lapilli, blocks and bombs. The lavas are essentially transitional basalts, and rhyolites. Transitional basalts are rather exceptional in the Cameroon Volcanic Line (CVL). The chemical composition of the minerals of these basalts is indicative of the thermobarometric conditions of their formation. In the locality of Nkoumelap situated to the West of the Bamoun plateau, they crystallized at low pressure (1.8 Kb) and relatively high temperatures (from 1110°C to 862°C in clinopyroxenes and 1044°C to 801°C in opaque minerals of transitional basalts) and differ significantly from the alkali basalts of the same plateau as well as from all the typical alkali basalts of the CVL. Measures of the distribution of volcanic products coupled to the volcanic history of the region could enhance understanding of the intensity of volcanic events and facilitate evaluation of induced risks. The Landstat 7 ETM+ data of the region was used to elaborate a hazards map of the zone, highlighting volcanic risks. This study, realized in the Bamoun plateau, is the baseline for a vast cartography program of the hazards and risks along the CVL. It could help to better protect the population and efficiently manage risks in case the volcanic activity is revived.