Weathering - The Breakup of Rocks
By Patti Hutchison
Air, water, ice, and gravity. These are nature's agents of
weathering. Weathering is the breaking down of rocks on
the earth's surface. This process has been going on since
the earth was formed.
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Have you seen pictures of the Grand Canyon? Do you
know how it was formed? You guessed it- weathering. The
water from the Colorado River carved the canyon through the rock around it.
Evidence of weathering is all around us.
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There are two kinds of weathering. The first is mechanical weathering. A
mechanic uses tools to take your car apart. Nature uses tools such as ice and water
to take rocks apart. This is also called physical weathering.
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Mechanical weathering doesn't change what the rock is made of. It simply
changes the size and shape of the rock. There are several ways a rock can be
weathered physically.
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Water and ice are common causes of weathering. Water collects in the cracks of
rocks. When water freezes, it expands. This can cause the rocks to split apart. They
break down into smaller rocks.
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Pressure is another tool for weathering. The weight of rock layers on top cause
pressure on rocks buried below the surface. Gravity can cause the top layers to be
removed. Then the pressure is released. The rocks expand and break apart.
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Roots of trees and plants can also cause mechanical weathering. They can grow
into cracks in rocks. As they do this, pressure on the rocks can cause them to break
apart.
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There is another form of weathering called chemical weathering. Water and
oxygen are the most common causes of chemical weathering. They cause chemical
changes in rocks.
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Water can dissolve many kinds of rocks and minerals. Rivers and streams
dissolve the minerals in their banks as they move. The rivers become wider or
deeper. The minerals are carried away by the current.
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Oxygen makes up about twenty-one percent of our air. It can combine with many
substances. When it does, the chemicals are changed. This is called oxidation.
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Iron is a substance that is easily oxidized. Iron in rocks and minerals combines
with the oxygen in air to form a different substance. If you have a rusty bike chain,
you have seen the effects of oxidation.
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Weathering has a great effect on our lives. Potholes in roads are caused by
weathering. Our cars rust. Statues and buildings wear away because of weathering.
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However, there is a good side to weathering. Weathering helps make soil.
Without soil, we would not be able to grow plants for food and to help put oxygen
back into the air. Look around you- the effects of weathering are everywhere.
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