**3.1 Field observations**

In the Caldera of the Mount Bambouto the flows, mostly trachytic, have extensions ranging from 150 to 250 m; with an average height of between 10 and 30 m.

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**Figure 3.**

*The Caldera of Mount Bambouto: Volcanological Characterization and Classification*

They are generally roughly and irregularly priced and are observable at the level of the caldera ramparts, on certain escarpments, road embankments and riverbeds. On the other hand, mafic lava flows are poorly represented in the caldera and have extensions of just a few meters. The domes are generally circular to sub-circular in shape with a base slightly above the top. They are dominated by coarse prisms and sometimes numerous diaclases which favor the sporadic detachment of polygonal blocks generally observable at their base. Felsic and mafic flows are also observable in polygonal blocks accumulated near caldera ramparts and on stream beds (**Figure 3**). The lava texture is mostly microlitic porphyritic except for ignimbrites,

*Some geological features of the Mount Bambouto caldera: (A–C)—post-caldera protrusions. (D)—erratic* 

*boulders; (E–G)—caldera's floor structure; and (H)—caldera rim.*

*DOI: http://dx.doi.org/10.5772/intechopen.93694*

which have a vitroclastic texture.

## *The Caldera of Mount Bambouto: Volcanological Characterization and Classification DOI: http://dx.doi.org/10.5772/intechopen.93694*

They are generally roughly and irregularly priced and are observable at the level of the caldera ramparts, on certain escarpments, road embankments and riverbeds. On the other hand, mafic lava flows are poorly represented in the caldera and have extensions of just a few meters. The domes are generally circular to sub-circular in shape with a base slightly above the top. They are dominated by coarse prisms and sometimes numerous diaclases which favor the sporadic detachment of polygonal blocks generally observable at their base. Felsic and mafic flows are also observable in polygonal blocks accumulated near caldera ramparts and on stream beds (**Figure 3**). The lava texture is mostly microlitic porphyritic except for ignimbrites, which have a vitroclastic texture.

### **Figure 3.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

discussion by many researchers nowadays.

**2. Method of study**

**2.1 The volcanological study**

*2.1.1 The petrographic study*

the model of [9].

**2.2 The classification of calderas**

logical studies and those existing in the literature.

understanding the functioning and evolution of the Mount Bambouto and, consequently, the dynamics of the Cameroon Volcanic Line, which remains a subject of

Several field trips were made. They made it possible to describe rock outcrops, take rock samples and take the coordinates of the various samples. These samples were then described and labeled. In the laboratory, the coordinates of the various rock sampling points were plotted on the topographic map of the study area. Through these different points and the macroscopic description of the samples, a geological map is produced [33]. In order to complete the macroscopic study of the rocks, thin sections of samples were taken at the University of Orleans and the University of Paris-Sud (Orsay Campus) in France. These thin sections were studied with the polarizing microscope of the Laboratory of Environmental Geology of the University of Dschang and at the Laboratory of Life and Earth Sciences of the University of Maroua. Some samples were analyzed with microprobe also at the University of Orleans and the University Paris-Sud (Orsay Campus) and in Nancy for the nomenclature of rock minerals and the determination of the nature of rocks. These microscopic and chemical studies have made it possible to refine the geological map of the caldera of the Mount Bambouto [33]. In addition, some complementary geochemical analyses were made to determine the chemical nature of different lavas.

*2.1.2 The volcanological evolution of the caldera of the mount Bambouto*

For the volcanological evolution of the caldera of the Mount Bambouto we have:

• carried out a cartographic study through the analysis of satellite images, about 70 aerial photos, digital elevation models, and topographic maps. This study allowed us to determine the exact boundaries and structure of the caldera.

produce through DTM, the different stages of caldera formation according to

• The geochronological data available in the literature made it possible to

For the classification of the Caldera of the Mount Bambouto, we used the Caldera DataBase from [14]. To do so, we used the data obtained through volcano-

In the Caldera of the Mount Bambouto the flows, mostly trachytic, have extensions ranging from 150 to 250 m; with an average height of between 10 and 30 m.

**282**

**3. Results**

**3.1 Field observations**

*Some geological features of the Mount Bambouto caldera: (A–C)—post-caldera protrusions. (D)—erratic boulders; (E–G)—caldera's floor structure; and (H)—caldera rim.*

Basalts, hawaiites and trachytes all have a grayish alteration patina and are less than 3 mm thick. However, this patina has, in some places, crystals of automorphic alkaline feldspar of 4 mm or less in size. Ignimbrites have a strong patina of less than 3 mm thick and are gray to brown.

### **3.2 Microscopic petrography**

*Basalts* (**Figures 4** and **5**) are characterized by a porphyritic microlitic texture in which pyroxene phenocrystals (10–25% of the rock), plagioclase (1–3% of the rock), olivine (2–7% of the rock) and opaque oxides (<3% of the rock) are embedded in a microlitic mesostase.

*Hawaiites* (**Figure 4**) are also characterized by a porphyritic microlitic texture in which pyroxene phenocrystals (2–5% of the rock), plagioclase (3–10% of the rock), olivine (15–35% of the rock) and opaque oxides (5–7% of the rock) are embedded in a microlitic mesostase.

*Mugearites* (**Figure 5**) are dominated by a subporphyritic microlitic texture materialized by amphibole (kaersutite), apatite and oxide phenocrystals. These phenocrystals constitute less than 10% of the rock. These rocks are kaersutite mugaearites.

Generally speaking, the *trachytes* (**Figure 4**) of the Mount Bambouto Caldera have a subporphyritic microlitic texture rich in phenocrystals of alkaline feldspar

### **Figure 4.**

*Drawings of some thin sections of rocks in the Mount Bambouto caldera: (A)—basalts; (B)—phonolites; (C)—kaersutite-mugearite; and (D)—ignimbrites.*

**285**

**Figure 5.**

*The Caldera of Mount Bambouto: Volcanological Characterization and Classification*

(30% of the rock), plagioclase, pyroxene (<4% of the rock), amphibole (<1% of the

*Phonolites* (**Figures 4** and **5**) show a light brown alteration patina of almost 3 mm thick. The fresh, greenish gray to greenish gray sample shows large crystals of alkaline feldspar (30% of the rock); 0.5 to 5 mm in size and some pyroxene granules. Microscopically, the rock has a subaphyric to porphyritic microlitic

*Photographs of thin sections of rocks in the Mount Bambouto caldera: (A, D, and H)—hawaiites;* 

rock), oxide (5% of the rock) and apatite.

*(B)—phonolites; (C, F, and G)—Basalts; (E)—trachytes.*

*DOI: http://dx.doi.org/10.5772/intechopen.93694*

*The Caldera of Mount Bambouto: Volcanological Characterization and Classification DOI: http://dx.doi.org/10.5772/intechopen.93694*

**Figure 5.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

than 3 mm thick and are gray to brown.

**3.2 Microscopic petrography**

ded in a microlitic mesostase.

a microlitic mesostase.

mugaearites.

Basalts, hawaiites and trachytes all have a grayish alteration patina and are less than 3 mm thick. However, this patina has, in some places, crystals of automorphic alkaline feldspar of 4 mm or less in size. Ignimbrites have a strong patina of less

*Basalts* (**Figures 4** and **5**) are characterized by a porphyritic microlitic texture in which pyroxene phenocrystals (10–25% of the rock), plagioclase (1–3% of the rock), olivine (2–7% of the rock) and opaque oxides (<3% of the rock) are embed-

*Hawaiites* (**Figure 4**) are also characterized by a porphyritic microlitic texture in which pyroxene phenocrystals (2–5% of the rock), plagioclase (3–10% of the rock), olivine (15–35% of the rock) and opaque oxides (5–7% of the rock) are embedded in

*Mugearites* (**Figure 5**) are dominated by a subporphyritic microlitic texture materialized by amphibole (kaersutite), apatite and oxide phenocrystals. These phenocrystals constitute less than 10% of the rock. These rocks are kaersutite

Generally speaking, the *trachytes* (**Figure 4**) of the Mount Bambouto Caldera have a subporphyritic microlitic texture rich in phenocrystals of alkaline feldspar

*Drawings of some thin sections of rocks in the Mount Bambouto caldera: (A)—basalts; (B)—phonolites;* 

**284**

**Figure 4.**

*(C)—kaersutite-mugearite; and (D)—ignimbrites.*

*Photographs of thin sections of rocks in the Mount Bambouto caldera: (A, D, and H)—hawaiites; (B)—phonolites; (C, F, and G)—Basalts; (E)—trachytes.*

(30% of the rock), plagioclase, pyroxene (<4% of the rock), amphibole (<1% of the rock), oxide (5% of the rock) and apatite.

*Phonolites* (**Figures 4** and **5**) show a light brown alteration patina of almost 3 mm thick. The fresh, greenish gray to greenish gray sample shows large crystals of alkaline feldspar (30% of the rock); 0.5 to 5 mm in size and some pyroxene granules. Microscopically, the rock has a subaphyric to porphyritic microlitic

## *Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

texture containing phenocrystals and microcrystals of alkali feldspars, pyroxene, feldspathoid, amphiboles and oxides.

*Ignimbrites* (**Figures 4** and **5**) have a vitroclastic texture dominated by a faciesdominated matrix and whole or broken sections of alkali feldspar, quartz, pyroxene, and rock enclaves (trachytes and basement) in the form of rounded balls or subangular fragments.
