Weathering & Erosion. What is weathering? Weathering is a set of physical, chemical and biological processes that change the physical and chemical properties.

Weathering & ErosionWeathering & Erosion

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 physical and chemical

properties of rocks and soil at properties of rocks and soil at or near the earth's surface.or near the earth's surface.

More about weatheringMore about weathering

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

are NOT MOVINGare NOT MOVING Weathering is part of the Weathering is part of the Rock Rock

CycleCycle

There are three types of There are three types of weatheringweathering

Mechanical [sometimes called Mechanical [sometimes called physicalphysical]]

ChemicalChemical Biological Biological

Mechanical weathering Mechanical weathering breaks breaks rocks down into smaller pieces. rocks down into smaller pieces.

Types of mechanical weathering Types of mechanical weathering include frost wedging, exfoliation, include frost wedging, exfoliation,

and thermal expansion. and thermal expansion.

Chemical weathering Chemical weathering breaks rocks breaks rocks down chemically adding or removing down chemically adding or removing

chemical elements, and changes chemical elements, and changes them into other materials. them into other materials.

Chemical weathering consists of Chemical weathering consists of chemical reactions, most of which chemical reactions, most of which

involve water. involve water.

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

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

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

relationship. relationship.

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

other chemicals.other chemicals.

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

composition.composition.

Enchanted Enchanted rock is a rock is a

huge huge example of example of exfoliation exfoliation mechanical mechanical weathering weathering

close to close to home.home.

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

In chemical weathering, a In chemical weathering, a rock is broken down by rock is broken down by chemical reactions that chemical reactions that

change its mineral change its mineral composition and physical composition and physical and chemical properties and chemical properties

Chemical weathering Chemical weathering happens when the minerals happens when the minerals

that make up a rock are that make up a rock are changed, leading to the changed, leading to the

disintegration of the rockdisintegration of the rock

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

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

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

the reactions.the reactions.

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

example, feldspar and quartz, example, feldspar and quartz, are common minerals in the rock are common minerals in the rock

granite, have very different granite, have very different levels of resistance to chemical levels of resistance to chemical

weathering. weathering. Quartz doesn’t weather very Quartz doesn’t weather very

easily, but feldspar does. Over a easily, but feldspar does. Over a long time, it chemically changes long time, it chemically changes

into clay minerals. into clay minerals.

Biological weathering Biological weathering involves processes that can involves processes that can

be either chemical or be either chemical or physical in nature.physical in nature.

Biological weathering can be Biological weathering can be considered special types of considered special types of

mechanical or chemical mechanical or chemical weathering.weathering.

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

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

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

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

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

Now let’s move on toNow let’s move on toEROSIONEROSION

What is erosion?What is erosion?

Erosion is defined as the removal Erosion is defined as the removal and movement of earth materials and movement of earth materials

by natural agents. by natural agents.

Some of these agents include Some of these agents include glaciers, wind, water, earthquakes, glaciers, wind, water, earthquakes, volcanoes, tornadoes, hurricanes, volcanoes, tornadoes, hurricanes,

mud flows, and avalanches.mud flows, and avalanches.

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 that often work together to break down rocks. Both processes occur down rocks. Both processes occur in place. No movement is involved in place. No movement is involved

in weathering.in weathering.

As soon as a rock particle (loosened by one As soon as a rock particle (loosened by one of the two weathering processes) moves, of the two weathering processes) moves,

we call it we call it erosionerosion or mass wasting. or mass wasting. Mass wasting is simply movement down Mass wasting is simply movement down

slope due to gravity. slope due to gravity. Rock falls, slumps, and debris flows are all Rock falls, slumps, and debris flows are all

examples of mass wasting. We call it examples of mass wasting. We call it erosion if the rock particle is moved by erosion if the rock particle is moved by

some flowing agent such as air, water or some flowing agent such as air, water or ice. ice.

In a nutshell: if a particle is In a nutshell: if a particle is loosened, chemically or loosened, chemically or mechanically, but stays mechanically, but stays

put, we call it weathering. put, we call it weathering. Once the particle starts Once the particle starts

moving, we call it erosion.moving, we call it erosion.

Water is the most Water is the most important erosional agent important erosional agent and erodes most often as and erodes most often as

running water in streams or running water in streams or rivers.rivers.

Water in all its forms is erosional. Raindrops Water in all its forms is erosional. Raindrops create create splashsplash erosionerosion that moves tiny that moves tiny particles of soil. Water collecting on the particles of soil. Water collecting on the

surface of the soil collects as it moves towards surface of the soil collects as it moves towards tiny streams and creates sheet erosion.tiny streams and creates sheet erosion.

Erosion by wind is known as Erosion by wind is known as aeolian erosion (named after aeolian erosion (named after

Aeolus, the Greek god of Aeolus, the Greek god of winds) and usually occurs in winds) and usually occurs in deserts. Aeolian erosion of deserts. Aeolian erosion of

sand in the desert is partially sand in the desert is partially responsible for the formation responsible for the formation

of sand dunes.of sand dunes.

Painted Desert National Painted Desert National MonumentMonument

The erosive power of moving ice is The erosive power of moving ice is actually a greater than the power actually a greater than the power of water. however since water is of water. however since water is

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

Glaciers cause erosion two ways - they Glaciers cause erosion two ways - they pluck and abrade. Plucking takes place pluck and abrade. Plucking takes place

by water entering cracks under the by water entering cracks under the glacier, freezing, and breaking off glacier, freezing, and breaking off

pieces of rock that are then moved by pieces of rock that are then moved by the glacier. Abrasion cuts into the rock the glacier. Abrasion cuts into the rock under the glacier, scooping rock up like under the glacier, scooping rock up like

a bulldozer and smoothing and a bulldozer and smoothing and polishing the rock surface.polishing the rock surface.

Athabasca Glacier - Jasper, Canada

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 awesome; large storm waves can produce 2000 pounds of can produce 2000 pounds of pressure per square foot. The pressure per square foot. The

pure energy of waves along with pure energy of waves along with the chemical content of the the chemical content of the

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

Wave action in Calvert County Maryland

The End!The End!

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