This week our Earth Science students were introduced to weathering and erosion. Here is a brief summary of the lesson:
How does the surface of the earth wear down?
There are several major processes which cause the earth to wear down.
They are physical weathering, chemical weathering and erosion.
Physical weathering is the actual breaking down of rock by the action of natural forces, such as water,
wind, plants and animals. One of the most common cause of physical weathering is due to the constant freezing and thawing of water in and around the rocks themselves.
Water frequently collects on rocks and gets into their small openings. When temperatures drop below
freezing, the water in these cracks turns to ice and expands. This exerts a tremendous amount of pressure on the openings in these rocks.
As temperatures rise and the ice melts back into its liquid form, it creeps deeper into the fractures. When the water freezes again, it further expands the openings in the rock. This cycle will go on day after day, year after year, until finally, a once huge mountainside could disintegrate to a pile of small
rock fragments.
Chemical weathering causes changes in the rocks from the reaction of different chemicals on the
surface of the rocks. One common example of chemical weathering is called oxidation.
If we were to leave an iron nail in a cup of water for a few weeks, a chemical change takes place. The nail gradually becomes coated with a dark red substance we call rust. Rust is oxidized iron. This rusting, or oxidation, deteriorates any surface on which it reacts and will eventually cause it to break down and fall apart.
The mineral iron is present in many different kinds of rocks and oxidation can break down these rocks if they are exposed to water for long periods of time.
