Bioerosion
Water, wind, ice and fire are not the only erosive forces on Earth. Animals, big and small can do major work in the shaping of landscapes. For example, burrowing animals dig holes through dirt, which destabilizes said dirt, often increasing the rate of downslope soil creep. Some microorganisms secrete acidic compounds that can react with rocks, chemically weathering them away. These are obviously not the only two examples.