What natural cause broke the sediment off the side of valley?

The natural cause that often breaks sediment off the side of a valley is erosion, typically driven by factors such as water runoff, freeze-thaw cycles, or gravitational forces. Heavy rainfall or rapid snowmelt can increase water flow, leading to soil saturation and slope instability. Additionally, the freeze-thaw process can weaken the bonds within the sediment as water infiltrates cracks, freezes, and expands. These processes collectively contribute to the gradual removal of sediment from valley sides.