Step 2: Erosion and Transport (Sediments on the Move!)

This stream carries sediment that has weathered from nearby mountains at Polychrome Pass, Alaska. Click on image for full size (30K JPG) Courtesy of Bruce Molnia, Terra Photographics

Sneeze into a pile of dust and the particles fly everywhere. Sneeze into a pile of rocks and they stay put. That’s because they have more mass. You need more force than a sneeze to move those rocks. Wind and water can have enough force to move rocks. Just compare what’s on the bottom of a fast moving river with what’s at the bottom of a calm lake. The fast moving river will carry away the smaller sediments leaving large gravel and even boulders. The calm lake allows even very small sediments carried in the water to settle to the bottom.

Moving water in rivers and moving air in wind sort particles by size. Larger particles can be carried in a stronger current, like fast moving water. Very small particles like silt and clay settle very slowly and so they only form layers at the bottom of quiet water areas like lakes, swamps, or lagoons.

The size of the sediments in a clastic sedimentary rock usually relates directly to the energy of the wind or water that they were deposited in. Particles that can sink to the bottom in a fast moving river must be very large and heavy. Smaller particles are carried away. However, in a calm lake, even very small pieces of sediment are able to settle to the bottom.

This stream carries sediment that has weathered from mountains in Alaska. Click on image for full size (30K JPG) Courtesy of Bruce Molnia, Terra Photographics

If you sneeze into a pile of dust, the little particles fly everywhere. But if you sneeze into a pile of rocks, they will stay put. It takes more force than a sneeze to move those rocks. Winds and water can have enough force to move rocks.

Larger pieces of sediment can be carried in a stronger current, like fast moving water. Very small particles like silt and clay can be carried by even slow current and settle very slowly. They only form layers at the bottom of quiet water areas like lakes, swamps, or lagoons.

The size of the sediment in a clastic sedimentary rock usually relates directly to the energy of the wind and water that they were deposited in. Sediment that can sink to the bottom in a fast moving river must be very large and heavy. Smaller particles are carried away. However, in a calm lake, even very small pieces of sediment are able to settle to the bottom.

This stream carries sediment that has weathered from mountains in Alaska. Click on image for full size (30K JPG) Courtesy of Bruce Molnia, Terra Photographics

If you sneeze into a pile of dust the little particles fly everywhere, but if you sneeze into a pile of rocks, they will stay put. It takes more force than a sneeze to move those rocks. Winds and water can have enough force to move rocks.

Very small pieces of sediment like mud and clay are picked up very easily by moving wind and water. But they can settle to the bottom of calm lakes or to the ground when the air or water stops moving.

Larger pieces of sediment can be carried in a stronger current, like fast moving water. Sediment that can sink to the bottom in a fast moving river must be very large and heavy.