Weathering & ErosionWeathering & Erosion

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What is weathering?What is weathering?

Weathering is a set of physical, Weathering is a set of physical, chemical and biological chemical and biological

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

earth's surface.earth's 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 three types of weatheringThere are three types of weathering

• Mechanical [sometimes called Mechanical [sometimes called physicalphysical]]

• ChemicalChemical

• Biological Biological

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 wedging, exfoliation, thermal frost wedging, exfoliation, thermal

expansion and abrasion.expansion and abrasion.

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.

Biological weatheringBiological weathering is the breakdown of is the breakdown of rock caused by the action of living rock caused by the action of living

organisms, including plants, burrowing organisms, including plants, burrowing animals, and lichens.animals, and lichens.

A lichen is a combination of fungus and algae, A lichen is a combination of fungus and algae, living together in a living together in a symbioticsymbiotic relationship. relationship.

Lichens can live on bare rock, and they break Lichens can live on bare rock, and they break down rocks by secreting acids and other down rocks by secreting acids and other

chemicals.chemicals.

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.

Observe photographs of Observe photographs of some of the different types some of the different types of mechanical weathering.of mechanical weathering.

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 - thermal expansion - heatheat• abrasion - abrasion - wind, waves, rain, glaciers, and so wind, waves, rain, glaciers, and so

on rub (abrade) rocks' surfaces, wearing them on rub (abrade) rocks' surfaces, wearing them down down

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

• http://www.youtube.com/watch?feature=player_embedded&v=6VnVRHIV6j4

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 Physical and chemical weathering occur together. Physical weathering occur together. Physical weathering

breaks rocks into pieces so more breaks rocks into pieces so more surface is exposed to chemical surface is exposed to chemical

weathering which breaks it down weathering which breaks it down further.further.

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, are common For example, feldspar and quartz, are 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.

Watch a movie about chemical Watch a movie about chemical weathering:weathering:

Review chemical Review chemical weathering:weathering:

scroll down the page to get scroll down the page to get to the topicto the topic

Biological weathering involves processes Biological weathering involves processes that can be either chemical or physical in that can be either chemical or physical in

nature.nature.

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

weathering.weathering.

Biological weathering – What is it?Biological weathering – What is it?

Some biological weathering Some biological weathering processes are:processes are:

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

• 2. Tree roots grow into cracks and widen 2. Tree roots grow into cracks and widen them, which helps physical weathering. them, which helps physical weathering.

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

Lichens on Lichens on rocks cause rocks cause

biological biological weathering.weathering.

Plants growing in rocks break Plants growing in rocks break the rocks apart.the rocks apart.

Image Courtesy United States Geological Survey; Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images Photo ID: h7fbtb | Photographer: Bruce Molnia US Geological Survey Copyright © Bruce Molnia, Terra Photographics

How are erosion & weathering How are erosion & weathering different?different?

Weathering involves two processes Weathering involves two processes [[mechanical, chemicalmechanical, chemical] ]

that often work together to break down rocks.that often work together to break down rocks. Both processes occur in place.Both processes occur in place.

No movement is involved in weathering. No movement is involved in weathering.

As soon as a rock particle moves, we call it As soon as a rock particle moves, we call it erosionerosion or or mass wasting. mass wasting.

If a particle is loosened, If a particle is loosened, chemically or mechanically, but chemically or mechanically, but

stays stays put, we call it weathering. put, we call it weathering.

Once the particle starts moving, Once the particle starts moving, we call it erosion.we call it erosion.

What are the different types of What are the different types of erosion?erosion?

• Wind

• Water

• Glaciers (Ice)

• Gravity

WaterWater in all its forms is erosional. in all its forms is erosional. Raindrops create Raindrops create splashsplash erosionerosion that moves tiny particles that moves tiny particles

of soil. of soil. Water moving on the surface of the soil collects as it Water moving on the surface of the soil collects as it

moves towards tiny streams and creates moves towards tiny streams and creates sheet erosionsheet erosion..

Mass Wasting is a form of ErosionMass Wasting is a form of Erosion

Observe river erosion Observe river erosion causing waterfallscausing waterfalls

Waves in oceans and other large Waves in oceans and other large bodies of water cause coastal bodies of water cause coastal

erosion. erosion.

The power of ocean waves is The power of ocean waves is awesome; large storm waves can awesome; large storm waves can produce 2000 pounds of pressure produce 2000 pounds of pressure per square foot. The pure energy per square foot. The pure energy of waves along with the chemical of waves along with the chemical

content of the water is what erodes content of the water is what erodes the rock of the coastline. the rock of the coastline.

Wave action in Calvert County Maryland

Watch wave erosionWatch wave erosion

Erosion by Erosion by windwind is known as is known as aeolian erosion aeolian erosion (named after Aeolus, the (named after Aeolus, the

Greek god of winds) Greek god of winds) and usually occurs in and usually occurs in deserts. deserts.

Wind erosion of sand in the desert Wind erosion of sand in the desert is partially responsible for the is partially responsible for the

formation of sand dunes.formation of sand dunes.

Painted Desert National Painted Desert National MonumentMonument

The erosive power of The erosive power of moving ice moving ice (glaciers) (glaciers) is actually a greater than the is actually a greater than the

power of water. power of water. However since water is much more However since water is much more

common, it is responsible for a greater common, it is responsible for a greater amount of erosion on the earth's amount of erosion on the earth's

surface. surface.

GlaciersGlaciers

Glaciers cause erosion two ways - they pluck Glaciers cause erosion two ways - they pluck and abrade. Plucking takes place by water and abrade. Plucking takes place by water entering cracks under the glacier, freezing, entering cracks under the glacier, freezing,

and breaking off pieces of rock that are then and breaking off pieces of rock that are then moved by the glacier. Abrasion cuts into the moved by the glacier. Abrasion cuts into the rock under the glacier, scooping rock up like rock under the glacier, scooping rock up like a bulldozer and smoothing and polishing the a bulldozer and smoothing and polishing the

rock surface.rock surface.

Athabasca Glacier - Jasper, Canada

Observe landscapes Observe landscapes formed by erosionformed by erosion

Unless otherwise noted, the Unless otherwise noted, the source for all photographs in source for all photographs in

this presentation isthis presentation is

• http://http://home.cc.umanitoba.chome.cc.umanitoba.ca/~benbow/a/~benbow/erosion1.htmlerosion1.html