Geology Reference
In-Depth Information
contribution in increasing the awareness of the local popu-
lation about
their geoheritage and the necessity for
its
management for local sustainable development.
According to Grandgirard ( 1997 ), Reynard ( 2005 ), a
geomorphosite is any part of the Earth
s surface that is
important for the knowledge of Earth, climate and life his-
tory. Panizza and Piacente ( 1993 , 2003 ) and Quaranta
( 1993 ), de
'
ned geomorphological sites as geomorphological
landforms and processes that have acquired a scenic/aes-
thetic, scienti
c, cultural/historical and/or a social/economic
value due to human perception of geological, geomorpho-
logical, historical and social factors.
2
Geological Context
Mt Manengouba was developed by successive emplacement,
from 1.55 to 0 Myr, on a 800 m uplifted granite-gneiss
substratum of two volcanoes, Elengoum and Eboga, and is
situated at about 120 km NE of Mount Cameroon. Mt Ma-
nengouba covers an area of 500 km 2 and occurs between the
Tombel and Mbo grabens, precisely between longitude
09
North
(Kagou Dongmo et al. 2005 ). The maximum height of the
whole volcano is 2,411 m and it is located at the south-
eastern external slopes of the Eboga caldera.
Mt Manengouba is surrounded by plutono-tectonic units
expressed geomorphologically as the Ekomane cliffs to the
north (1,685 m), Mount Bakossi to the west (1,678 m),
Mount Koup
°
42
and 10
°
10
East and, latitude 04
°
49
and 05
°
15
Fig. 2 Geological map of Mt Manengouba. 1 alluvium; 2 recent
adventive strombolian volcanoes, with cones and basaltic
ows; 3
diatremes-related hyaloclastites in the Eboga caldeira and at Djeu-seh; 4
mugearite extrusions in the Eboga caldeira; 5 piles of basalt and hawaiite
fl
fl
é
to the south-west (2,064 m) and Mount
Nlonako to the south-east (1,825 m).
Mt Manengouba was characterized by adventive
anks; 6 mac to intermediate lavas
and tephras of the Eboga central edice; 7 intermediate to acidic
(trachytes) lavas of the Elengoum volcano emplaced before the Eboga; 8
old trachytic outpourings, mainly ignimbritic; 9 relative substratummade
of Mio-pliocene basaltic plateau
ows of the Eboga middle and lower
fl
ssural
volcanism that gave rise to more than 70 strombolian cones;
some of them were initiated by phreato-magmatic explosive
events (Kagou Dongmo et al. 1998 ). Numerous rocks occur
at Mt Manengouba such as basalts, hawaiites, mugearites,
benmoreites trachytes, dolerites and pyroclastic ejecta (sco-
ria) (Figs. 2 and 3 ). The outcrop expression of these rocks
results in several geomorphological units that comprise the
uneven topography of Mt Manengouba.
ows; 10 pre-volcanic Cenozoic
intrusion of syenite; 11 Precambrian granito-gneissic shield; F, fault;
FS, ssural system; C, caldera scarp. (From Kagou Dongmo et al. 2005 )
fl
2010 ), as in the volcanic terrains in the Park of Fogo Island,
Cape Verde (Costa 2011 ). To assess the Mt Manengouba
landforms, we undertook a review of the criteria to determine
intrinsic values (scienti
c) and additional values (ecological,
aesthetic, economic and cultural) used by Gray ( 2004 ), Pereira
et al.( 2006 , 2007 ), Reynard et al. ( 2007 ), Reynard ( 2008 ), Ilies
and Josan ( 2009 ), Pereira and Pereira ( 2010 ), Maillard and
Reynard ( 2011 ) and Reynard and Coratza ( 2013 ). The geo-
morphosites that characterize Mt Manengouba are calderas,
broken cones, crater lakes, domes, plug, and basin.
2.1
The Geomorphological Features of Mt
Manengouba
The high geodiversity (lithological diversity) and the tectonics
in this area have been the main in
uence in developing its
distinctive geomorphological features (Meireles et al. 2002 ;
Pereira et al. 2004a , b ). In Mt Manengouba, as well as in other
volcanoes along the CVL, tectonic events have been under-
lined by eruptive events (Tchoua 1972 ; Marzoli et al. 2000 ;
Zangmo et al. 2011b ; Gountie et al. 2011 ). These events cre-
ated four major volcanic landforms, namely, cones, domes,
cliffs and lava plateau (Wandji 1995 ; Kagou Dongmo et al.
fl
2.1.1 Calderas
Mt Manengouba stands as an example of a Hawaiian shield.
At the summit, there are two sub-circular nested calderas:
Elengoum and Eboga (Fig. 4 ). The larger one is the Elen-
goum caldera, some 6
7 km in diameter, but its margins
-
appear diffuse. The
fl
oor of Elengoum is occupied by the
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