Rain-induced weathering dissolution of limestone and implications for the soil sinking-rock outcrops emergence mechanism at the karst surface: a case study in southwestern China

Carbonate weathering by rain is considered to play an important role in the karst landform evolution. Rock outcrops (or stone teeth) are frequently visible on the earth’s surface, especially in karst landscapes, but there is no consensus on how they appeared or increased in number. This study estimated the extent of rain-induced weathering dissolution of limestone using hydro-chemical data from a karst area enjoying a subtropical monsoon climate, and proposed a mechanism of soil sinking and rock outcrops emerging, based on the assumption that the dissolved subsoil limestone is the main cause of geomorphic reworking of the karst surface topography. By calculation, the weathering dissolution rate of subsoil limestone is greater than the residue formation rate by dissolution of exposed and subsoil limestone in both forested and cleared karst surfaces, and soil sink at a rate of 0.126 mm a −1 in forested and 0.111 mm a −1 in the cleared karst, implying relative growth of exposed limestone and the spontaneity of the karst process. Besides, smaller values of subsoil dissolution rate and soil sinking rate in the cleared than in the forested demonstrate that soil sinking and rock outcrops emergence are both slower without the cover of forests, while the opposite was true for dissolution of exposed limestone, implying that deforestation may not an absolute promoting factor to karst landscape. This soil sinking model provides a new explanation for the changes in the soil–rock position relationship, which is contrasting with the traditional karst soil loss model that generally attributes rock emergence to soil slope erosion or/and underground soil leaks.