This stream carries sediment that has weathered from nearby mountains at Polychrome Pass, Alaska.
Click on image for full size
Courtesy of Bruce Molnia, Terra Photographics
Step 2: Erosion and Transport (Sediments on the Move!)
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.
Last modified August 25, 2003 by Lisa Gardiner.
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