Small pieces of rock often break down further through: weathering folding irrigation volcanoes

The correct answer is - weathering.

The weathering is the process that manages to break down the rocks into very small particles. It can come in multiple different ways, like through the influence of mechanical or chemical ways, but the end result is always the same, the rocks are losing small particles little by little, and over time there's nothing left from them. The weathering is a process that has the tendency to flatten the landscape, so it manages to create a balance between the rising up of the landscape, with its flattening.