Weathering and The Rock Weathering and The Rock CycleCycle

WeatheringWeathering

• Weathering is the breaking down of rocks into sediments. After the rocks have been broken other forces carry the rocks away.

• Weathering affects rocks, caves, mountain and even buildings and streets. Different types of weathering (chemical and mechanical) break down earth’s surface and have changed what we see over billions of years. Mountains becomes hills.

Mechanical WeatheringMechanical Weathering

• Mechanical weathering occurs when rocks are broken apart by physical processes. – The rocks actually disintegrate but the overall

chemical make-up of the rock stays the same. Each piece of rock is similar to the original rock. It is like a jackhammer smashing up rock.

– Growing plants, burrowing animals, and expanding ice can mechanically weather rocks. Enough force is created to break the rocks into smaller pieces.

The Major Types of Mechanical The Major Types of Mechanical Weathering are:Weathering are:

• 1.) Frost Wedging

• 2.) Exfoliation/ Uploading

• 3.) Organic Activity

Mechanical Weathering – Frost Mechanical Weathering – Frost WedgingWedging

• When water enters the cracks in a rock and freezes, it expands.

• The cracks enlarge and the rock breaks apart.

• Then more water can enter the crack, freeze and expand, causing the cracks to grow bigger. This processes also breaks up roads

Freeze Thaw CycleFreeze Thaw Cycle

Freeze Thaw CycleFreeze Thaw Cycle

Mechanical Weathering - Mechanical Weathering - ExfoliationExfoliation

• The rock weathers and erodes away

• There is less weight and pressure pushing down on the rock

• The rock expands upward under reduced pressure and breaks into sheets and slabs.

Mechanical Weathering - OrganicMechanical Weathering - Organic

• Water and nutrients that collect in the cracks of a rock allow plants to grow.

• Plant roots grow into rocks and split it apart

• Burrowing animals, such as earthworms and moles can loosen sediments.

Mechanical WeatheringMechanical Weathering

• Once a rock weathers, its surface area increases, thus the surface area exposed allows for more weathering

Chemical WeatheringChemical Weathering

• Chemical Weathering occurs when chemical changes dissolve the minerals in rocks or change the minerals into different minerals.

• Occurs when rocks react with air, water and other chemicals.

• 2 major types of chemical weathering:– Oxidation– Acid reactions

Chemical Weathering - OxidationChemical Weathering - Oxidation

• When rocks containing iron are exposed to air and water

• The rocks oxidize or “rust” producing a red colour – A rusty nail or bike chain

Chemical Weathering – Acid Chemical Weathering – Acid ReactionsReactions

• When water reacts with carbon dioxide it produces carbonic acid.

• The acid reacts with the rocks that contain calcite (Limestone)

• Rocks like Limestone will dissolve from the acid.

Factors affecting WeatheringFactors affecting Weathering

• 2 Major factors affecting weathering are:– Mineral Composition of Rock

• Some minerals are less stable and dissolve faster than others

– Climate of a region• The warmer and more wet a region is, the more

weathering occurs• Climate affects both mechanical and chemical

weathering

Rock CycleRock Cycle

• Rocks can be broken apart, chemically altered, dissolved and carried away by water and ice. Once the rock reaches a new location, it can undergo even more changes and become part of an entirely different family of rocks. Sedimentary rocks can become metamorphic rocks. Metamorphic rocks can become igneous rocks.

Rock CycleRock Cycle

• The ROCK CYCLE consists of the processes in which rocks are continually changed over long periods of time.

How the Rock Cycle WorksHow the Rock Cycle Works

• Many foods are made by the same processes that rocks undergo in the rock cycle.

• How is chocolate fudge like an igneous rock? (heating and cooling)

• How is a granola bar like a sedimentary rock? (different types of sediments cemented together)

• How is a grilled cheese sandwich like a metamorphic rock? (how heat transforms the cheese)

Bonus ActivityBonus Activity

• Complete a diagram and write-up with your class a food you could use to represent processes in the rock cycle. Explain the similarities between rocks and your food. Discuss what steps of the food preparation represent processes in the rock cycle.