by the temperature of a region plus the amount of rainfall it receives. As the amount of
precipitation increases, so does the rate of solution and the number of chemical reactions.
In general, as the amount of rainfall increases, so does the degree of weathering. Remember
that water is an agent of both mechanical and chemical weathering, so when water is not
available, the rate of weathering slows tremendously. Two amazing examples of preservation
include mummification and freezing. Both of these situations occur in the absence of liquid
water. Therefore a dry climate will produce the lowest rate of weathering, followed by a
very cold climate, regardless of the amount of rainfall it receives. The rates of highest
weathering would occur in a wet climate that is also warm or hot. As the temperature of a
region increases, so does the rate of chemical reactions. For each 10oC increase in average
temperature, the rate of chemical reactions doubles. The warmer a climate is, the more types
of vegetation it will have and the greater the rate of biological weathering. This happens
because plants and bacteria grow and multiply faster in warmer temperatures. If you want
an easy way to remember these examples, think about where you would put your sandwich if
you want it to stay fresh for a while. How quickly does it go bad in your lunch box? Where
would you put food from the grocery store if you wanted to save it for a week or more?
Some resources are actually concentrated for us by the actions of weathering. In tropical
climates, intense chemical weathering carries away all soluble minerals, leaving behind just
the least soluble components. The aluminum oxide, bauxite forms this way and is our main
source of ore for producing aluminum. The actions of moving water can also concentrate
heavier minerals, like gold. This process fueled the gold rush out west in North America in
the 1800’s.
Lesson Summary
- Mechanical weathering breaks existing rock into smaller pieces without changing the
composition of the rock. - Ice wedging and abrasion are two important processes of mechanical weathering.
- The main agents of mechanical weathering are moving water, wind, glacial ice and
gravity. - Chemical weathering decomposes or breaks down existing rock, forming new minerals
that are stable at the Earth’s surface. - Water, carbon dioxide and oxygen are important agents of chemical weathering.
- Different types of rocks weather at different rates. More resistant types of rocks will
remain longer.
Review Questions
- Name two types of mechanical weathering. Explain how each works to break apart
rock. - What are three agents of chemical weathering? Give an example of each.