The rocks that make high ridges are much more resistant to weathering than the surrounding rocks.
Click on image for full size
Courtesy of Jerome Wyckoff
Step 1: Breaking Rocks Apart
Over time, rocks wear away just like your favorite jeans or the bottom of your
shoes. This is called weathering. There are two ways that it can happen. Either
rocks wear away chemically, or they physically break apart.
Wearing away chemically
Sometimes the minerals in a rock are dissolved into rainwater just like table
salt dissolves in a glass of water. Other times, minerals are chemically changed
from one type into another. Not all minerals are likely to be weathered in this
way. For instance, the mineral quartz doesn’t weather very easily, but
feldspar does. Over a long time, feldspar changes into clay.
Breaking apart physically
Sometimes rocks are broken apart into smaller pieces. This can happen when water
flowing in rivers and streams tumble rocks and when ocean waves hit the rocks
along a rocky coastline. Tree and plant roots can push rocks apart as they grow.
If water freezes into cracks in a rock it will expand as it freezes, opening
the crack even more.
The little pieces of rock are either moved away by water or wind, or they become
a part of the soil.
Last modified December 31, 2003 by Lisa Gardiner.
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The Fall 2010 issue of The Earth Scientist
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