D. G. Nkouathio

The Tombel graben (West Cameroon): a recent monogenetic volcanic field of the Cameroon Line

The Tombel graben is a recent monogenetic volcanic field located in the continental part of the Cameroon Line. Magmatic activity began with fissure eruptions emitting large lava flows, and continued with explosive episodes generating cinder cones. Tombel lava flows are made up of three major rock types. Ankaramite yields phenocrysts of Fe–Ti oxides, forsterite olivine and diopside-augite clinopyroxene. In addition to this assemblage, basalt and hawaiite (olivine basalt, doleritic basalt and trachybasalt according to their modal compositions) contain phenocrysts of labradorite-andesine plagioclase and scarce kaersutite. The suite of lava flows, ranging from ankaramite to hawaiite, define an incomplete sodic alkaline series. Moreover, basanite, rich in incompatible elements, is locally found as late ejecta. Geochemical data share some oceanic island basalt (OIB) characteristics. It is suggested that the ankaramite–hawaiite series could be due to differing degrees of partial melting of a source at the asthenosphere–lithosphere boundary, followed by low rates of fractional crystallization.

Mapping and Assessment of Volcanic Hazards Related to the Ignimbritic Eruption by AMS in Bambouto Volcano (Cameroon Volcanic Line)

Pyroclastic deposits constitute major components of explosive volcanic activity. To help improve the safety of the population faced with natural disasters, a study is carried out at Bambouto volcano with a view to map potential hazards related to pyroclastic flows. The Bambouto volcano is indeed considered to be still active since the recent discovery of Quaternary basalts (0.5 Ma) at Totap, a locality situated near the Bambouto Caldera. This discovery has led to reclassify Mount Bambouto among active volcanoes of Cameroon and, therefore, considered as potentially dangerous. The dangerousness of this volcano is accentuated by the presence of ignimbrites that are witnesses of ancient pyroclastic flows. Because a map of volcanic hazards is non-existent on the volcano, anisotropy of magnetic susceptibility (AMS) is the method used in this paper to characterize magnetic fabrics and provides an estimate of flow direction of each ignimbrite sheet (represented by massive lapilli tuff and massive lithic breccia facies). Inferred transport directions based on the AMS data and field indicators show that Bambouto Caldera is the source of main pyroclastic deposits of Mount Bambouto. These results have enabled us to produce a new hazard map related to potential future pyroclastic flows.

Geomorphological Features of the Manengouba Volcano (Cameroon Line): Assets for Geotourism and Other Anthropogenic Activities

Mount Manengouba, a volcanic complex emplaced between 1.5 and 0 Myr, occurs in the Cameroon Line, about 120 km NE of Mount Cameroon, Cameroon. Mount Manengouba culminates at 2,411 m and is characterized by important geomorphological features (geomorphosites), namely, two nested sub-circular calderas (Elengoum and Eboga), broken cones, crater lakes (Female, Male and Beme), and domes and basin (Djeu-Seh). These geomorphosites constitute an asset for geotourism and other anthropogenic activities. The scientific values (rareness, representativeness, integrity…) and additional values (aestheitic, ecological, economic…) Mount Manengouba geomorphosites constitute an enterprise for geotourism. The fertility of the soil favours farming in the downslope areas of the volcano, with the main products being coffee, maize, bananas, fruit and tubers. Hunting and fishing are practiced by craftsmen throughout the year in the forests and Female Lake, respectively. Vegetation cover fosters the practice of animal breeding (beef and sheep) in both calderas and their vicinities. The presence of pyroclastic cones are utilised for quarrying in the region. Pozzolana is the main product that is used as road aggregates, and in the manufacture of concrete, bond-stones and cement. Excursions and research programs are carried out by universities for educating the public about the geological and geomorphological heritage of Mount Manengouba. Currently, in the Mount Manengouba region, tourism is not well developed, but it is recommended that, roads be improved to facilitate the accessibility to the geomorphosites, and interpretative panels, guide books and postcards be produced to inform tourists about the geology of the region.

The Volcanic Geoheritage of the Mount Bamenda Calderas (Cameroon Line): Assessment for Geotouristic and Geoeducational Purposes

The Mount Bamenda is a stratovolcano with summit calderas situated in the Cameroon Line, precisely between Bambouto and Oku volcanoes. It is made up of two main Late Miocene ignimbritic calderas: Lefo and Santa-Mbu that present interesting volcanological heritage. This heritage is made up of numerous geomorphosites namely Mount Lefo, Dome West, Dome East, West Rim, Dome Awing, Awing Lake, Dome Mbu 1, Dome Mbu 2, Mount Manah and Mbu Valley. They have been assessed using a method developed at the University of Lausanne by Reynard et al. (2015). The average scientific value of the geomorphosites is 0.77, because they are well preserved (0.95), rare (0.88) and representative (0.78) of the local geomorphology and principal features. They also play significant role for Bamenda volcano’s geographical history in the way that they modified the previous natural and rural landscapes. Although several geomorphosites did not play cultural role, their ecological and aesthetic value that has been qualitatively assessed is high. There are not sound nuisances around the majority of geomorphosites. The rareness of high vegetation or infrastructures gives rise to several panoramic viewpoints of geomorphosites. Besides, these sites have meaningful features that can be described for geotourists so that they can learn about their evolution or formation. Through these assets, Mount Bamenda calderas are the possible geotouristic and geoeducational destinations. Geotourism could be an opportunity for rural development, and it could contribute to efforts in alleviating poverty and rural migration. In order to improve tourist offers and raise the Mount Bamenda calderas in geopark in the future, some recommendations have been suggested.

Geohazards (floods and landslides) in the Ndop plain, Cameroon volcanic line

Abstract The Ndop Plain, located along the Cameroon Volcanic Line (CVL), is a volcano-tectonic plain, formed by a series of tectonic movements, volcanic eruptions and sedimentation phases. Floods (annually) and landslides (occasionally) occur with devastating environmental effects. However, this plain attracts a lot of inhabitants owing to its fertile alluvial soils. With demographic explosion in the plain, the inhabitants (143,000 people) tend to farm and inhabit new zones which are prone to these geohazards. In this paper, we use field observations, laboratory analyses, satellite imagery and complementary methods using appropriate software to establish hazard (flood and landslide) maps of the Ndop Plain. Natural factors as well as anthropogenic factors are considered. The hazard maps revealed that 25% of the area is exposed to flood hazard (13% exposed to high flood hazard, 12% to moderate) and 5% of the area is exposed to landslide hazard (2% exposed to high landslide hazard, 3% to moderate). Some mitigation measures for floods (building of artificial levees, raising foundations of buildings and the meticulous regulation of the flood guards at Bamendjing Dam) and landslides (slope terracing, planting of trees, and building retaining walls) are proposed.