2. The natural process by which rock is broken into smaller pieces. The process of moving sediment by water, wind, or ice.

3. River rocks (upstream) are larger and more jagged. River rocks (downstream) are smaller and smoother.

5. Nile River Amazon River Mississippi River

6. Groundwater erodes soft rock underground forming a cave. Gravity, and extra weight on top, may cause the roof to collapse.

8. After heavy rains, water saturates the top layers of soil. Then gravity causes soil, mud, and rocks to slide quickly downhill.