What is Weathering?What is Weathering?

Weathering is a set of physical, chemical, and biological

processes that change the physical and chemical properties of rocks and soil at or near the

earth's surface.

More about WeatheringMore about Weathering

• Weathering is the breakdown of rock Weathering is the breakdown of rock to form sediment [very small pieces of to 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 three types of WeatheringThere are three types of Weathering

• Mechanical [also called Mechanical [also called physicalphysical]]• ChemicalChemical• BiologicalBiological

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 expansionAbrasionAbrasion

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.

Types of Mechanical WeatheringTypes of Mechanical Weathering • Frost wedging Frost wedging –– rocks break downrocks break down when ice in cracks expands. Shatteredwhen ice in cracks expands. Shattered rocks are common in cold climates rocks are common in cold climates where repeated freeze-thaw cycles where repeated freeze-thaw cycles gradually pry rocks apart. This type ofgradually pry rocks apart. This type of weathering also causes pot holes. weathering also causes pot holes.

• ExfoliationExfoliation - rock breaks off into - rock breaks off into sheets or layers that are parallel sheets or layers that are parallel to the earth’s surfaceto the earth’s surface

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.

Thermal expansion and contraction Thermal expansion and contraction extreme heating and cooling of rock can shatter rocksextreme heating and cooling of rock can shatter rocks

AbrasionAbrasion - - wind, waves, rain, glaciers,wind, waves, rain, glaciers,abrade the rocks’ surfaces, wearing them downabrade the rocks’ surfaces, wearing them down

Types of Mechanical Weathering Types of Mechanical Weathering

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 materials. elements, and changes them into other materials.

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

Chemical Weathering

Rock is broken down by chemical reactions that change its mineral composition and physical and chemical properties. Rocks are broken down by chemical actions (O2, H2O, CO2).

It is the transformation or decomposition of one mineral into another.

Water is most often a part of 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.

Chemical WeatheringA stalagmite rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate .

Stalactites are formed by the deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions. Limestone is calcium carbonate rock which is dissolved by water that contains carbon dioxide forming a calcium bicarbonate.

Acid Rain• Compounds from burning coal, oil and gas

react chemically with water forming acids.• Acid rain causes very rapid chemical

weathering

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.

Feldspar to clayFeldspar to clay

+ H2CO3

(carbonic acid)

Karst Topography• A type of landscape in rainy regions where

there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams.

• Created by chemical weathering of limestone.

A Karst landform is a feature created on the Earth's surface by the drainage of water into the ground or by its discharge at springs. The term derives from Kras, a region in western Slovenia where typical karst forms such as sinkholes, caves, natural bridges and sinking streams were first studied in detail.

Karst LandformsKarst Landforms

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

Biological Weathering can be bothchemical and mechanical in nature.

Biological Weathering• Biological weathering is the breakdown of rock

caused by the action of living organisms, including plants, burrowing animals, and lichens.

• Biological weathering can be considered special Biological weathering can be considered special types of mechanical or chemical weathering.types of mechanical or chemical weathering.

Biological WeatheringBiological Weathering

1. Rocks can break because of animal burrowing.1. Rocks can break because of animal burrowing.

2. Tree roots grow into cracks and widen them, 2. Tree roots grow into cracks and widen them, which helps physical weathering. Roots also which helps physical weathering. Roots also produce acids to help break down rock. produce acids to help break down rock.

3. Bacteria, lichens and other organisms secrete 3. Bacteria, lichens and other organisms secrete acidic solutions, which helps chemical weathering. acidic solutions, which helps chemical weathering.

Living Organisms• 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. • Lichens that grow on rocks produce weak acids that

chemically weather rock.

Biological Weathering

Weathering RatesWeathering Rates• Chemical weathering happens quickly in warm, moistChemical weathering happens quickly in warm, moist environments because water is needed for the environments because water is needed for the chemical reactions. chemical reactions.

• The warm weather speeds up the reactions. The more waterThe warm weather speeds up the reactions. The more water means there will be more weathering. means there will be more weathering.

• Surface area exposure: more surface area = greaterSurface area exposure: more surface area = greater weatheringweathering

Weathering RatesWeathering Rates

• Climate-dictates the temperature and amount of moistureClimate-dictates the temperature and amount of moisture• #1 factor in weathering process#1 factor in weathering process

• Mineral composition-the harder the rock, the slower the Mineral composition-the harder the rock, the slower the rate of weathering, composition dictates resistance to rate of weathering, composition dictates resistance to weatheringweathering