Weathering is the process that slowly breaks down rocks, soil, and minerals on Earth’s surface. These forces, like air, water, or living things, work over long periods to change the land right where the rock is located.
The Different Ways Rocks Break Down
The forces that break down the Earth’s surface can be sorted into three main groups based on how they work. Mechanical weathering uses physical force to split material into smaller fragments. A common example is when water seeps into a rock’s crack and then freezes, expanding like a wedge of ice and forcing the crack to widen.
Another process is chemical weathering, where the material’s makeup is changed by a reaction, much like ingredients changing when you bake a cake. This often happens when water mixes with carbon dioxide in the air to create a weak acid, which can then dissolve certain minerals in rocks. The reddish-brown rust you might see on an old bike is an example of this, as oxygen in the air reacts with iron in the metal, weakening it and causing it to crumble.
Living things also cause changes through biological weathering, which involves plants, animals, and tiny organisms. Tree roots, as they grow, can push into small cracks in rocks or pavement, exerting enough pressure to split them open. Even tiny organisms like lichens can slowly break down rock by releasing weak acids onto the surface.
Weathering Versus Erosion: What is the Difference?
People often confuse weathering with erosion, but they describe two separate steps that work together. Weathering is only the breaking or crumbling of the material, which happens while the rock remains mostly in its original spot.
Erosion, however, is the movement of those broken pieces, called sediment, from one place to another. The forces of nature, such as wind, flowing water, or ice, carry the tiny fragments away.
Therefore, weathering must happen first to create the small pieces, and then erosion moves those pieces to a new location. These two processes constantly reshape Earth’s surface, working together to carve canyons and change coastlines over vast amounts of time. The Colorado River, for instance, first weathers the rock walls and then erodes the fragments downstream, making the Grand Canyon wider and deeper.
Seeing Weathering Happen Around You
You can spot the effects of weathering in many places right in your neighborhood. Look closely at the sidewalks and driveways after a cold winter, and you might see new cracks or potholes. These are often caused by mechanical weathering as water froze, expanded, and pushed the pavement apart.
If you visit a river or creek, the smooth, rounded stones along the bank show the results of mechanical weathering, as the water tumbled them against other rocks. Older metal structures or statues that have been outside for many years often have a faded or rusted appearance. This color change and weakening is due to chemical weathering from oxygen and acid rain.
Even the small weeds or grass pushing up through the asphalt in a parking lot show biological weathering in action. The ground beneath your feet is always being broken down and changed by these slow, powerful forces.