www.whyville.net Apr 26, 2009 Weekly Issue

Staff Writer

Stirring Up Science: Mechanical Weathering

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Mechanical weathering is when Mother Nature breaks down parts of the Earth a little at a time. This action takes long periods of time to actually break down something.

Scientists have put mechanical weathering in four categories:

1. Temperature Change
2. Frost Action
3. Root Action
4. Animal Activity

Temperature changes are when there are sudden changes of temperature. Here is an example:

Say you had a rock in a hot desert. You leave it there over a period of time. The sun literally bakes the rock, allowing the rock to expand (grow bigger). When it's night in the desert, it gets really cold. This means that the rock contracts (grows smaller). When this happens over and over again, the rock becomes fatigued, meaning it strains the rock. Eventually, this fatigue to the rock makes them start to crack. Finally over time, the rock begins to crumble, a bit at a time. This is mechanical weathering, called temperature change.

Frost action is when water (one of the few things that actually expands when it's frozen) is seeping through an item. When the water reaches freezing point, it freezes and expands, allowing a crack to form in that item.

If a rock had gets water on it and there were many tiny cracks in the rock, left untouched in under freezing point weather, the water would expand. When the water expands, it cracks open the little cracks even more. When this happens again and again, the cracks become bigger. When the cracks finally get big enough to crack open a rock, they will. This is how frost action works, and it's also under mechanical weathering.

Root action is a bit different.

When a tree or a shrub has roots that are growing into rocks, the roots usually break the rocks. This is because the roots are so strong and can withstand many obstacles and natural disasters.

Animal activity is also a different one.

Animals don't actually contribute to mechanical weathering. The way they live can contribute to it though.

When some animals dig into the ground, they dig holes, sometimes big holes. These holes let in air and water. When the air and water are let in under the ground, they can weather the rocks, meaning do frost action and temperature to the rocks, causing unbalanced or uneven ground.

These are just some causes of mechanical weathering. It's very interesting, so tune in next week for the chemical weathering! This is Nateenka, signing off.

Author's Note: Sources: 8th grade science class and teacher, 8th grade science book


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