WeatheringWeathering

What is weathering?What is weathering?

Weathering is a set of physical Weathering is a set of physical and chemical processes that and chemical processes that

change the physical and change the physical and chemical properties of rocks and chemical properties of rocks and

soil at or near the earth's soil at or near the earth's surface.surface.

More about weatheringMore about weathering

• Definition – the breakdown of rock to Definition – the breakdown of rock to form sediment [very small pieces of form sediment [very small pieces of rock]rock]– Weathering happens to rocks that are Weathering happens to rocks that are

NOT MOVINGNOT MOVING

– Weathering is part of the Weathering is part of the Rock CycleRock Cycle

There are two types of weatheringThere are two types of weathering

• Mechanical [also called Mechanical [also called physicalphysical]]

• ChemicalChemical

Mechanical weathering Mechanical weathering breaks rocks breaks rocks down into smaller pieces, but does not down into smaller pieces, but does not change the composition of the rock. change the composition of the rock.

Types of mechanical weathering include: Types of mechanical weathering include: Frost wedgingFrost wedgingExfoliationExfoliationThermal expansionThermal expansionRoot pryRoot pryAnimal activityAnimal activityAbrasionAbrasion

Chemical weathering Chemical weathering breaks rocks down breaks rocks down chemically adding or removing chemical chemically adding or removing chemical elements, and changes them into other elements, and changes them into other

materials. materials.

Chemical weathering consists of chemical Chemical weathering consists of chemical reactions, most of which involve water. reactions, most of which involve water.

The mechanical breakdown of rock The mechanical breakdown of rock caused by the action of living caused by the action of living

organisms, including plants and organisms, including plants and burrowing animalsburrowing animals

Let’s investigate Let’s investigate mechanical weatheringmechanical weathering first. first.

Click to see a video clip about mechanical weathering

In mechanical weathering, a rock is In mechanical weathering, a rock is broken down into smaller pieces broken down into smaller pieces

without changing its mineral without changing its mineral composition.composition.

Enchanted Enchanted rock is a huge rock is a huge

example of example of exfoliation exfoliation mechanical mechanical weathering weathering

close to home.close to home.

Review mechanical weathering:Review mechanical weathering:• breaks rocks down into smaller pieces.breaks rocks down into smaller pieces.

Types of mechanical weathering includeTypes of mechanical weathering include• frost wedging – frost wedging – ice in cracks expandsice in cracks expands• exfoliationexfoliation - rock breaks off into sheets - rock breaks off into sheets • thermal expansion and contraction – thermal expansion and contraction – heating and heating and

coolingcooling• abrasion - abrasion - wind, waves, rain, glaciers, and so on rub wind, waves, rain, glaciers, and so on rub

(abrade) rocks' surfaces, wearing them down (abrade) rocks' surfaces, wearing them down • Root Pry and Animal ActionsRoot Pry and Animal Actions —living things —living things

physically changing rockphysically changing rock

Now, let’s look at Now, let’s look at chemical weatheringchemical weathering. .

In chemical weathering, a rock is In chemical weathering, a rock is broken down by chemical reactions broken down by chemical reactions that change its mineral composition that change its mineral composition

and physical and chemical and physical and chemical properties.properties.

Water is most often a part of Water is most often a part of chemical weathering.chemical weathering.

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

Physical and chemical weathering occur together. Physical and chemical weathering occur together. Physical weathering breaks rocks into pieces so Physical weathering breaks rocks into pieces so more surface is exposed to chemical weathering more surface is exposed to chemical weathering

which breaks it down further.which breaks it down further.Click to watch the video.Click to watch the video.

Chemical weathering happens Chemical weathering happens quickly in warm, moist quickly in warm, moist

environments because water is environments because water is needed for the chemical needed for the chemical

reactions.reactions.

The warm weather speeds up the The warm weather speeds up the reactions.reactions.

Not all minerals are prone to chemical Not all minerals are prone to chemical weathering. weathering.

For example feldspar and quartz, common For example feldspar and quartz, common minerals in the rock granite, have very different minerals in the rock granite, have very different

levels of resistance to chemical weathering. levels of resistance to chemical weathering.

Quartz doesn’t weather very easily, but feldspar Quartz doesn’t weather very easily, but feldspar does. Over a long time, it chemically changes does. Over a long time, it chemically changes

into clay minerals. into clay minerals.

Lichens on rocks Lichens on rocks cause chemical cause chemical

weathering.weathering.

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

Review weathering:Review weathering:

scroll down the page to review all three scroll down the page to review all three types of weatheringtypes of weathering