In terms of erosion susceptibility, which is the least erodible soil type?

Gravel is recognized as the least erodible soil type due to its larger particle size and the fact that it tends to be less cohesive compared to finer soils like silt or clay. The larger particles in gravel allow water to flow through more easily, which reduces the potential for erosion since the turbulent force of flowing water has a harder time displacing these larger particles.

In contrast, silt and clay soils are much finer and tend to hold water differently. Silt can easily be transported by water due to its fine particles while clay has a tendency to clump together, but when disturbed, it can also be easily eroded. Sand falls somewhere in between; while individual grains are larger than silt or clay, sand can still be mobilized by wind or water flow. Therefore, gravel holds its place as the most stable among these soil types when considering erosion susceptibility.