Exfoliation is a weathering process in hard rocks by which alternate cycles of heating and cooling (expansion and contraction) cause rocks to breakdown mechanically into thin sheets/slabs along their outer surfaces- this is why it is also called “onion-skin weathering”. These sheet/slabs vary in thickness from a few centimetres to few meters.
Ok, let’s go and see some amazing onion-skin weathering sites in south-west Nigeria. We choose Akure, Ondo State capital. The young folks have given the town the street name “Ak-city”. It’s their own ‘small Lagos’ anyways (hahaha… yeye people).
Akure area is characterized by a landscape composed of a basal migmatite-gneiss country rock and granite intrusions, shooting out and outcropping ubiquitously as picturesque inselbergs in different places. These granites (porphyritic) are southern extensions of the Ikere-Ado Batholith.
On these granite inselbergs, we find numerous awe-inspiring rock formations formed by down-slipped exfoliating slabs/sheets. However, only a few of these rock formations qualify as caves and are called Talus Caves. While talus itself are the rock boulders/blocks produced from weathering, talus caves are those cavities and openings formed between the boulders piled up when pilled up.
Now, those talus caves found in Akure area range in form and size. Some appear to have been formed in-situ, while some appear to have been transported to their locations. Also, some differ from others in the type of geometry of the talus/blocks that formed them. These observations have therefore formed the basis of Kolawole & Anifowose (2011)’s review of the pre-existing classification of talus caves by Vidal & Vaqueiro (2007).
Over time, the rock formations of Akure area have been given special attention because of the seemingly precarious but spectacular and interesting poise assumed by the boulders. Iho-Eleeru is located in Isarun village, some 20mins from the outskirts of Akure. It is also known as the “Cave of Ashes” because of the burnt pottery works of the ancient dwellers at the cave. Aba Cave is located on the northern outskirts of Akure, and is given the name because it takes the form of a traditional hut. There is also Kinihun Rock, a massive pile of awe-inspiring rock boulders beautifully set on one another. It takes the form of a lion's skull when viewed from the north-eastern direction, hence it’s name.
These beautiful works of nature on the Nigerian soil proves to possess great and inestimable tourism potentials if properly explored and exploited, as they are not found in every other part of the world due to unsuitability of climatic conditions to facilitate their process of formation. For talus caves to be produced, the tropical climate is the most suitable due its relatively high temperature and humidity conditions.
*In future posts, we shall explore the process of formation of each of these talus caves.
1. Kolawole F. & A. Y. B. Anifowose (2011). Talus Caves: Geotourist Attractions Formed by Spheroidal and Exfoliation Weathering on Akure-Ado Inselbergs, Southwestern Nigeria. Ethiopian Journal of Environmental Studies and Management Vol. 4 No.3 2011. Pp1-6 (www.ajol.info/index.php/ejesm/article/view/71622/60586).
2. Vidal Romaní J. R. and M. R. Vaqueiro (2007). Types of granite cavities and associated speleothems: genesis and evolution. Nature Conservation 63. Pp41-46.