Re: How are sediments deposited (i.e., Grand Canyon)?

Sediments are fine particles of various substances that are formed in one 
location and then carried to other locations by water, wind, or glaciers.  
Most sediments that we are familiar with are particles of rock or clay 
that were formed or deposited in a higher location and then were 
transported to a lower location by flowing water. At the lower location 
the particles settle out of the water and form a layer on the stream bed, 
lake bed, or ocean floor.  

The smaller a particle of sediment is, the slower it will settle in 
water.  You can see this if you shake a jar of water that contains some 
mud and sand.  The sand will settle quickly and the mud more slowly.  Some 
of the really fine mud will stay in the water a long time.  In a moving 
stream of water a particle of sediment will be carried if the stream is 
moving fast enough that the turbulence of the water does not give the 
particle enough time to settle to the bottom.  The larger particles will 
settle to the bottom when the water becomes a calmer but very small 
particles will not settle until the water is practically still. 

Sediments are formed in a number of ways. Some are:
  Grinding by the movement of glaciers
  Ash from volcano eruptions
  Erosion from flow of water
  Blasting by windblown particles
  Freezing and thawing – the expansion of freezing water can break off 
tiny particles of rock

The Grand Canyon is a part of the Colorado River, which begins in the high 
mountains of Colorado and ends in the Pacific Ocean.  It is an example of 
the formation of sediment and its transport.  The river flows rapidly out 
of the mountains, picking up any sediment in its path, and depositing very 
little because it is moving so fast.  Where it is moving especially 
rapidly it gradually (over thousands and thousands of years) wears out the 
rocks over which it is flowing and turns them into sediment which it 
carries along.  This is how the Grand Canyon was formed.  The fast moving 
water from the mountains gradually wore a giant trench or canyon in the 
earth. The sediment that was created by the formation of the canyon was 
carried downstream and deposited where the river flows more slowly, or all 
the way to the ocean.

If you dig into sediment that was deposited over many years it may contain 
a number of layers.  This happens because the earth is always changing and 
the sediment that a stream picks up and carries can change.  For example, 
volcanoes can erupt, there can be centuries of bitter cold (called ice 
ages), when glaciers extend into warm area and grind up rocks as they 
move, and humans can disturb the earth by mining or removing trees to 
clear the  land for crops. When these things happen water flowing through 
these places will pick up a different kind of sediment which will be 
deposited on a layer over the old sediment. 

Good luck on your science fair project.