Weathering is any process which wears down solid structures over time. Generally, it refers to the breakdown of rocks and soil. But, it actually includes a range of processes that shape our world. This includes even man-made structures, like buildings and cities. As we’ll see, the Earth is constantly being shaped by this force.
A road which has been weathered by use and, of course, weather.
Everything in Motion
Earth contains lots of mighty structures and landforms. Mountains, volcanoes, and our own tallest buildings stand out in what seems to be a changing world. While plants and animals are always on the move, these things stay the same. And sure, they might not change during our lives. But, like everything else, they are subject to weathering. It’s a force which can topple anything, given enough time. For this reason, it’s essential to our understanding of landforms. Once rock structures form, they’ll always break down. This process reduces them to their original components.
Huge boulders. Sometime in the future, they will weather away.
And how does this happen? Most of the time, pretty slowly. That’s because weathering is a gradual process. Conversely, there are cases when it happens quickly. Landslides are an example of fast, dangerous version of this force. Yet, this is an exception. More often than not, the process takes a lot of time. Across seasons, water freezes inside of rocks, cracking them apart. Oxygen from the atmosphere rusts metal in buildings years after they’re built. Plants grow around boulders. Their spreading roots create pressure.
This old building likely took a long time to rust.
Each of these forces is an example of weathering. As you can see, there’s quite a wide variety. So, scientists have created a way to classify (and possibly prevent) them.
Types of Weathering
There are three main types. To be clear, these are broad categories. None of them are completely separate. Plants, as organisms, cause biological weathering. But, they do so by physically breaking up rocks and releasing chemicals onto them. What this tells us is that we have to look at the following types carefully.
Mechanical weathering refers to the physical separation break-up of a material. It’s a pretty broad category. So, here are some examples to clarify:
Wind shears a rock.
When wind blows against a solid surface, it’s pushing against it. The push is small, of course. But, over time, all the pushing adds up. It might chip pieces off of the solid. If they end up blowing far away, we call it wind erosion.
Ocean waves smash into the coast.
Coastlines often have very unique shapes to them. That’s because waves weather them over time. Each new wave digs into the rock a little. Much later, the digging can produce interesting patterns.
Small waves break against coastal rock.
The next type of weathering we’re going to look at is a little different. We can’t usually watch it happen. It takes place at the atomic level. But, we can learn from examples of what we know as chemical weathering.
Hydrolysis is when water, chemically known as H₂O, reacts with a rock to form a new material. This can happen when rainwater hits the igneous rock granite. Some of the minerals in granite react with water to form clay. This is an example of weathering because the new clay is much easier to erode.
Leaching is a simple, but important force. It’s when rainwater, which is naturally acidic, dissolves rocks. This happens a lot with limestone (a type of sedimentary rock). If runoff moves through a deposit of limestone, it might create a cave.
A cave. Caves are created by chemical weathering.
Our last type is actually quite simple. It’s when a living thing does any sort of weathering. It usually refers to soil: Animals dig through it, and plants grow in it.
Meerkats weather the soil by digging holes through it.
Weathering Vs. Erosion
The distinction between weathering and erosion is minor. Weathering breaks things up while erosion breaks them up and carries them away. The only difference is where the sediment ends up.
Other Great Resources:
Crash Course Video on the topic: