**5. Conclusion**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

that of ignimbritic materials [49, 50].

is an indicator of a relative chronology of the rocks. Indeed, there was an anteignimbritic trachytic volcanic phase. This means that there has been in the course of the evolution of the Bambouto volcano, the eruption of trachytic rocks before

The caldera of Mount Bambouto was formed at a well-defined time. The stages of formation of these calderas correspond globally to the model of [9]: a regional tumescence, a volcanic eruption, a collapse of the caldera, volcanism on the annular fractures and sedimentation. The present structure of the caldera floor shows that the roof of the magma chamber collapsed piecemeal during its formation. The border faults generally observed on calderas in certain volcanic environments in Cameroon, which are evidence of the different phases of caldera collapse, are difficult to observe in the caldera of Mount Bambouto. These faults, when identifiable on certain ramparts, present a some stages of collapse (**Figure 3**). In this caldera, the ramparts are often confused with the floor. The latter constitutes the most dissected floor of all the caldera units studied along the Cameroon Volcanic Line and their arrangement in decreasing steps from west to east, would testify to the multiple collapses that marked its formation [51, 52]. On the other hand, in the Eboga and Lefo calderas, where the ramparts are clearly visible from the caldera floor, there are boundary faults marked by about 2–4 stages of collapse [29]. Post-caldera volcanism has manifested itself on the Mount Bambouto. This has been observed in other caldera environments on the Cameroon Volcanic Line, notably the Santa-Mbu and Lefo caldera in the Bamenda Mountains, the Eboga and Elengoum calderas in Mount Manengouba and the Bangou caldera in Mount Bangou. It is at the origin of numerous doleritic, phonolitic and trachytic protrusions and, cones and maars found on the floor and external slopes of these calderas [33, 51–54]. These post-caldera geomorphological units give the caldera of Mount Bambouto the S and MS types according to [14]. Mount Bambouto constitutes a stratovolcano [20, 33]. The shape of this caldera is comparable to the elliptical shape of the calderas of Suswa, Kenya [55] and Chã das of Fogo Island in Cape Verde [56] and the calderas of the basaltic shields described by [9, 57]. This shape results from the geometry of the magma chamber which is the main factor controlling the final morphology of the calderas [58]. The presence of ignimbrites, tuffs, trachytes and rhyolites in the caldera of the Mount Bambouto qualifies it as an ignimbrite caldera. Ignimbrite calderas are usually over 10 km in diameter and over 1 km in depth, formed after the voluminous deposition of silicic ignimbrites [9, 11, 59]. We can list the example of Batur Caldera in Bali, New Zealand [60]. However, the term ignimbrite caldera is clearly used by (2015) [61] to qualify the calderas of the Southern Rocky Mountain Volcanic Field in Colorado (USA) notably Bonanza, Bachelor, Cochetopa Park, Creede, and Platoro calderas. Their presence in Mount Bambouto is explained by the fact that, considering the ages, this massif is sufficiently old compared to the other massifs, especially Mount Manengouba, because these acid magmas, according to [62], require a significant period of time for their formation to be elaborated.

Calderas are places where several natural hazards occur, including volcanic eruptions and mass movements [63, 64]. According to [65], calderas are destructive volcanic forms because they cause pre-existing reliefs to collapse, unlike postcaldera cones and domes, which are constructive because pre-existing reliefs are put in place. Moreover, the volcanic formations that cover them favor the formation of fertile soils and the development of a plant cover of various species conducive to an agropastoral activity [16]. These are environments where hydrothermal activities and mineralization processes generally occur [57, 66, 67]. In this respect, it is clear that calderas have a strong educational value as they allow us to understand the complexity of certain craters in volcanic environments around the world. As

**292**

The Caldera of Mount Bambouto is a volcanic unit that formed at a period between 18.68 and 22 Ma. Its emplacement model is comparable to that of Cole et al. 2005. Its formation and evolution gave it a rather varied petography and a characteristic structure. Its classification according to the Caldeira DataBase of Geyer and Marti (2008) allows us to conclude that its type of collapse is piecemeal. Chemically, the caldera is alkaline with codes ALKAf, ALKAi, and ALKAm. Furthermore, this caldera was formed through a continental rifting of extensional type, and their postcaldera protrusions give them Type-S and Type-MS. Moreover, it is a well-preserved caldera because its ridge lines are well observable.

The classification of the caldera of Mount Bambouto made within the framework of this work makes it possible to understand the similarities of this caldera with other calderas around the world on the one hand and to understand part of the global dynamics of the functioning of the Cameroon Volcanic Line on the other hand. Furthermore, this study contributes to elucidate the origin of the Cameroon Volcanic Line, which is still a subject of discussion among Cameroonian and foreign researchers today. Moreover, through this work, the Mount Bambouto Caldera is promoted next to the world scientific community that is still ignoring his existence.
