Weathering is the process that wears down rock formations. Mechanical weathering occurs when rocks are chipped away or broken such as if water seeps into a crack and freezes thereby expanding and breaking the rock apart. Chemical weathering can occur when the chemical composition of a rock or mineral is disrupted. For example, rainwater mixing with limestone leads to chemical weathering
Erosion, on the other hand, occurs when pieces or rock or sand are blown about or get caught in river currents and are brushed against other rocks (leading to mechanical weathering).