Weathering

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What is weathering? Weathering is a set of physical and chemical processes that change the physical and chemical properties of rocks and soil at or near the earth's surface.

More about weathering Definition – the breakdown of rock to form sediment [very small pieces of rock]Definition – the breakdown of rock to form sediment [very small pieces of rock] –Weathering happens to rocks that are NOT MOVING –Weathering is part of the Rock Cycle

There are two types of weathering Mechanical [also called physical]Mechanical [also called physical] ChemicalChemical

Mechanical weathering breaks rocks down into smaller pieces, but does not change the composition of the rock. Types of mechanical weathering include: Frost wedging Exfoliation Thermal expansion Root pry Animal activity Abrasion

Chemical weathering breaks rocks down chemically adding or removing chemical elements, and changes them into other materials. Chemical weathering consists of chemical reactions, most of which involve water.

The mechanical breakdown of rock caused by the action of living organisms, including plants and burrowing animals The mechanical breakdown of rock caused by the action of living organisms, including plants and burrowing animals

Let’s investigate mechanical weathering first. mechanical weathering mechanical weathering Click to see a video clip about mechanical weathering

In mechanical weathering, a rock is broken down into smaller pieces without changing its mineral composition.

Enchanted rock is a huge example of exfoliation mechanical weathering close to home.

Review mechanical weathering: breaks rocks down into smaller pieces.breaks rocks down into smaller pieces. Types of mechanical weathering include Types of mechanical weathering include frost wedging – ice in cracks expandsfrost wedging – ice in cracks expands exfoliation - rock breaks off into sheetsexfoliation - rock breaks off into sheets thermal expansion and contraction – heating and coolingthermal expansion and contraction – heating and cooling abrasion - wind, waves, rain, glaciers, and so on rub (abrade) rocks' surfaces, wearing them downabrasion - wind, waves, rain, glaciers, and so on rub (abrade) rocks' surfaces, wearing them down Root Pry and Animal Actions —living things physically changing rockRoot Pry and Animal Actions —living things physically changing rock

Now, let’s look at chemical weathering.

In chemical weathering, a rock is broken down by chemical reactions that change its mineral composition and physical and chemical properties. Water is most often a part of chemical weathering.

Chemical weathering happens when the minerals that make up a rock are changed, leading to the disintegration of the rock.

Physical and chemical weathering occur together. Physical weathering breaks rocks into pieces so more surface is exposed to chemical weathering which breaks it down further. Click to watch the video. Click to watch the video. Click to watch the video.

Chemical weathering happens quickly in warm, moist environments because water is needed for the chemical reactions. The warm weather speeds up the reactions.

Not all minerals are prone to chemical weathering. For example feldspar and quartz, common minerals in the rock granite, have very different levels of resistance to chemical weathering. Quartz doesn’t weather very easily, but feldspar does. Over a long time, it chemically changes into clay minerals.

Lichens on rocks cause chemical weathering. A lichen is a combination of fungus and algae, living together in a symbiotic relationship. Lichens can live on bare rock, and they break down rocks by secreting acids and other chemicals.

Review weathering: scroll down the page to review all three types of weathering