The soil factor of geodiversity – perspectives on erodibility classification in the Soutpansberg, South Africa

Soil diversity is one of the factors considered in geodiversity assessment. Its classification is usually based on expert knowledge of soils. One way of expert classification is through soil erodibility. High erodibility is allocated a high diversity class. Notwithstanding the debate on erodibility computation, soil classification for geodiversity based on erodibility is not a straightforward matter. Empirical evidence from the Soutpansberg range in South Africa reveals that high erodibility does not directly translate to a higher geodiversity. Though other factors may also play a role, river networks and slope angles are directly influenced by soil erodibility. Rivers follow easily erodible terrain while highly erodible soils create plains. Soils with high clay content tend to promote surface runoff. The cementing effect of clay promote strong substrates that can support a bigger angle of repose. Slopes and river channels in the Soutpansberg do not readily conform with this general anticipation. Rivers do not always coincide with high soil erodibility. Steep slopes do not always coincide with low soil erodibility. Neither do they always coincide with low soil erodibility. This leads to the conclusion that the contribution of erodibility to landform development and diversity is contextual rather than generic. Other factors such as aggradation and degradation may have to be considered in soil factor classification.

 

Key words: soil erosion; geodiversity; erodibility; hydrology; slope.