Soil

Soil is a mixture of weathered rock, micro-organisms, and organic remains that cover bedrock.

Its composition depends on the rocks that weathered and the local climate.

Physical weathered rocks break into small particles.  Chemical weathered rocks change minerals and often increase clay content.  Plants and animals add waste products and dead organisms.  They also burrow through and circulate water and air.  This will change the soils texture.

The gradual formation of soil in place produces layers we call horizons.  The top layer is the best layer for growing crops.  It is rich and dark and covered with organic matter we can call humus   (Not the food!!).  Some important minerals find their way to being transported deeper, usually by water. The lowest layer of soil is usually covered with broken bedrock.   Obviously the most weathering occurs on the top layer or Horizon A because it is exposed to all kinds of physical and chemical agents.  This area will also contain the most organic material.

In New York State, we do not usually show the complete development of soil profiles because much of our top layers were created as a result of glaciers moving southward and pushing everything in their way to our area.  So many of our rocks and soils actually originated far north of us and were broken down and transported as a result of the end of the ice age.
  
Soil Profiles-

Top layer- Horizon A- Top Soil- color gray to black and filled with organic
                        Material

2nd layer- Horizon B- subsoil- Usually red or brown, (lots of clay that has
                        Been washed downward)  Often the color comes from oxidation
                        Of minerals on Horizon A

3rd layer- Horizon C- Slightly weathered  parent material (rock fragments)
                                    From the bedrock that sits below.

 

 

Mass Movement of Soil-

      When we talk of mass movement, we are talking about a lot of soil moving at one time.   Gravity causes soil and rock fragments to fall, slide or move slowly down a slope.    Creep is the word we use for slow, downslope movement of soil

 

            Talus is a pile of rock fragments found at the base of a slope.  Talus piles are often found at the bottom of a cliff.

 

            Landslides are sudden movements, when bedrock or loose rock moves down a slope.  An avalanche is a landslide made of snow, ice or rock or mixtures of all of the above.

 

            Mudflow is the rapid movement of water saturated clay and silt.  It is especially fast and dangerous.

 

Protecting the Soil-  We need soil to grow food.  Human technology has contributed to the loss of soil by moving rocks for building, we do not have natural weathering of these rocks.  By destroying plant cover, like deforestation, more water gets to the soil and carries it away.  Salt used to melt ice on roads adds unwanted minerals to the soil and makes it difficult to grow things as a result.  We need to have undisturbed soil with plant covering and natural growth and weathering of rock in order for our world to continue to develop.