Spatial distribution of inselbergs in Igbajo district of Western Nigeria

Abstract

Inselbergs’ spatial distribution is the primary focus of this study carried out in Igbajo District of Western Nigeria. Additionally, a common hypothesis that spatial distribution of inselbergs is informed by the differing modes of evolution of the landforms was also examined. Inselbergs are defined as points on the topographic sheet and satellite terrain elevation data and are thereafter subjected to point pattern analysis. Two point pattern analyses: Poisson Probability Distribution (PPD) and Nearest Neighbour Analysis (NNA) are employed to determine the pattern of inselberg distribution over space. Additional analysis focused on the relationship between regional river drainage and inselbergs’ spatial distribution. Findings from the study confirmed that inselberg form a clustered distribution. The PPD results suggest that the observed distribution of inselbergs has a statistically significant difference from the expected pattern generated by the random process (c² test statistic = 49.82 >  =12.59 (α= 0.05) and 16.81 (α= 0.01). Similarly, the NNA with a R < 1 (Nearest Neighbour Ratio, R = 0.92) and p-value = -2.52, also indicated a clustered distribution. Analysis of river drainage pattern similarly revealed a cluster of high rising landforms situated in the centre of the regional watershed. It is concluded that inselberg distribution in the study area is clustered although the observed pattern does not necessarily validate or invalidate the alternative evolutionary theories.