spring sapping

Spring sapping is a geological process where an overlying resistant material is undermined by weathering or water flow in an underlying less-resistant material. This process, when driven by groundwater outflow, can contribute to the development of valleys, particularly through headward growth at valley heads. Groundwater emerges along a spring line, fostering chemical weathering that weakens the rock and makes it susceptible to erosional undercutting. This leads to slope undermining and collapse.1

The process is self-enhancing as groundwater flow converges on the spring head, accelerating weathering and erosion. This headward erosion proceeds faster than valley widening. Over time, this can form a network of valleys, especially in areas with structural weaknesses like joints and faults. Excellent examples of valleys formed by sapping are found in the sandstone terrains of the Colorado Plateau.1