Weathering and erosion are similar in that they both work together to change and shape the Earth's surface. While weathering breaks rock and earth down, erosion is the displacement of the pieces and particles of rock and earth.
Weathering breaks down and degrades the surface of the Earth through mechanical or chemical processes. Mechanical weathering happens when rocks break apart in response to environmental effects. Water is an important weathering agent as it infiltrates rock crevices. If the water carries salt, the build-up of salt begins to crack the rock due to pressure. Water inside rocks can also freeze and crack the rock. Invading tree roots and tunneling animals also cause rocks to crack apart.
Chemical weathering is often the result of water with some acid content, either from the air or soil. This acid dissolves rock, causing it to break or wear away. Limestone is especially prone to dissolution by chemical weathering. Water flow hollows out limestone formations to create tunnels and cave systems.
Water is also an important factor in erosion. The same water flow that seeps into rocks to freeze and crack them or that transports acids to wear away limestone, also carries away the broken or worn pieces.