Slow Changes to the Earth’s Surface Weathering, Erosion and Deposition

Our Changing Earth You have already learned that the earth’s surface is constantly changing and that some changes happen very quickly. Not all changes are rapid. Some changes happen over hundreds, thousands, millions or even billions of years. These changes happen because of 3 processes: weathering, erosion and deposition. Unlike rapid changes, which only happen in certain locations and at certain times, weathering, erosion and deposition happen all the time all over the world.

Weathering Weathering is one process that changes the surface of the earth very slowly. Weathering occurs when rock is broken down into smaller pieces. Weathering happens over a long period of time and is usually caused by three main agents: wind water ice

Weathering by Wind You might not believe it, but wind can actually break rock. Wind rubs off tiny pieces of rock. Sand blowing in the wind can rub away rocks even faster! Over time, the shape of the rock begins to change. Take a look at this rock: What did the rock most likely look like millions of years ago? What caused the arch to form? What might the rock look like a thousand years from now?

Weathering by Water Moving water is a powerful weathering agent! As it rubs against rocks, it causes small pieces to break loose. Over thousands or millions of years, water can wear away a lot of rock! Take a look at this picture: What wore the holes in the cliffs by the sea? What will most likely happen to these cliffs in the future?

Weathering by Ice You might not believe it, but ice can break huge rocks into pieces. That’s because water expands, or grows, when it freezes. Here’s how it happens: Liquid water seeps into small cracks in the rock. When the temperature drops below 0°C, the water freezes and expands. The ice pushes against the rock with enormous force causing the rock to crack or break into pieces.

Other Weathering Agents Besides wind, water and ice, there are several other agents that can cause weathering. The force of gravity can pull rocks down. Plants growing near rocks can break them apart. Chemical agents, such as acid rain, can wear rocks down.

What happens next? Once rock has been weathered by wind, water or ice, it often gets carried away. This is called erosion. There are 3 agents of erosion: wind water ice

Erosion by Wind The wind can carry sand, dust and small bits of rock from one place to another. The stronger the wind, the more erosion.

Erosion by Water As water runs downhill, it picks up particles of dust and rock. These particles are called sediment. Moving water, such as run-off, streams and rivers carry sediment across the land. The stronger the flow of water, the more sediment it can carry.

Erosion by Ice Ice, in the form of glaciers can erode rock too. A glacier is a large, moving sheet of ice. As a glacier slowly moves across the land, it can pick up rocks and other debris and carry them along. Glaciers are powerful enough to erode even very large rocks!

Deposition What happens to the sediments being carried by wind, water and ice? Eventually, these particles are deposited, or put down, in a new location as the wind, water or ice slows or stops. This process is called deposition. Deposition often results in the formation of new land as in this picture of a river bank.

Wrapping it Up Slow changes to the land always happen in this order: Weathering – the breaking down of rock by wind, water and ice Erosion – the movement of weathered rock by wind, water and ice Deposition – the dropping of weathered rock in a new location by wind, water and ice

What do you see: weathering, erosion or deposition?

What do you see: weathering, erosion or deposition?

What do you see: weathering, erosion or deposition?

What do you see: weathering, erosion or deposition?

What do you see: weathering, erosion or deposition?