Weathering, Erosion Weathering, Erosion & Deposition& Deposition

THINK!!!!THINK!!!!

Imagine the tiniest rock you have ever found. How did it get so small? It didn’t start out that way! What forces created this rock?

Weathering is the breaking down of rocks and other materials on the earth’s surface

What is the What is the difference difference between between

weathering and weathering and erosion?erosion?

• Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animals

• Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

What are the What are the twotwo types of weathering?

2 Types of WeatheringMechanical/Physical

Weathering processes that break a rock or mineral into

smaller pieces without altering its

composition

Chemical Weathering processes that

change the chemical composition of rocks

and minerals

What is Mechanical/Physical What is Mechanical/Physical Weathering?Weathering?

A rock is physically changed without a change in chemical composition

Processes include:• Frost Action / Ice Wedging• Abrasion by wind and water• Plant and Animal Action• Thermal Expansion and contraction • Pressure Unloading / Exfoliation

Frost Action / Ice WedgingFrost Action / Ice WedgingAlternating freezing and thawing of water

causes material to break up• Example – Pot holes, Ice cubes in an

ice tray• Water expands between 4 and 0

degrees Celsius

Volume increases by 9%!!!!

The Bigger the crack gets, the more water it lets in……causing a snowball effect

Frost Action / Ice Wedging

AbrasionAbrasionWearing down or smoothing of a

material due to constant collisions• Example – Beach glass, sandblasting• Breakdown caused by friction• Rocks become rounded• Waterfalls may result

Abrasions

Plant and Animal ActionPlant and Animal Action• Plant root growth and uplift

fracture rocks• Animals burrowing also cause

breakdown of rocks• Actions also increase the

exposure of rocks to air and water

Plant Action

Lichen (moss) on a rock or growth of tree out of the rock

Animal Action

Thermal Expansion and Thermal Expansion and ContractionContractionExtreme changes in

temperature may cause cracking

Pressure Unloading / Pressure Unloading / ExfoliationExfoliation

Cracking at weak joints due to a release of pressure

Cause and effect of Exfoliation• Rock breaks off into leaves or sheets along

joints which parallel the ground surface• Expansion of rock due to uplift and erosion• removal of pressure of deep burial• Occurs often in bedrock when glaciers

recede

Exfoliation• Peeling away of surface layers, caused by changes

in temperature, pressure or vegetation (trees, grass, vegetation growing on rocks.)

• Roots wedge into pores and cracks, splitting the rock

Dome Exfoliation

What is Chemical What is Chemical Weathering?Weathering?

The Chemical composition of the rock is altered causing a change

in properties

Processes include:•Hydrolysis•Oxidation•Acid Reactions / Carbonation

HydrolysisHydrolysisReaction of water with other

substancesChange is a very slow process

Examples are:

Feldspar Kaolinite

Anhydrite Gypsum

Kaolin mine in Central Georgia

OxidationOxidationWhere Oxygen combines with

other substances to produce rust

Oxidation in the presence

of water takes on a

reddish- yellow brown

color

Oxidation of basalt

Acid Reactions / Acid Reactions / CarbonationCarbonation

Carbon reacts with other substances to alter the chemical makeup of

rocksExample: Carbonic acids (water + carbon dioxide) dissolve limestone

which can results in the formation of underground caves

Nitric acids produced by the decay of organic material can alter soil composition

Caves are formed when Carbonic Acid dissolves

limestone

Stalactites (from the top) and Stalagmites (from the bottom) are formed in a limestone cave as a result of Chemical Weathering

Acid Rain has a drastic effect on rocks!

Nitric Acids in Soil

When organisms or plants decay Nitric Acid is produced. This is absorbed into the soil and the chemical make-up of the soil has been changed.

Differential WeatheringDifferential WeatheringThe variable rate of which rocks weather is called differential weathering

Factors affecting the rate of weathering include:

•Composition (granite vs. limestone) •Climate (hot, wet, cold, dry) •Rock size (surface area)

Rocks weather at different rates due to differences in mineral composition. The harder the rock, the slower the rate of weathering is.

Some minerals are more Stable at the earth’s surface than others! These take longer to weather. Composition dictates hardness which determines resistance to weathering.

The climateclimate that a rock is in is a factor in the rate of weathering.

Warm, wet climates – chemical weathering breaks down rocks rapidly

Cold Climates– mechanical weathering breaks down rocks rapidly

In which shape will weathering occur

faster?

How much exposed area of the rock will How much exposed area of the rock will

also effect weatheringalso effect weathering

EROSION/DEPOSITIONEROSION/DEPOSITIONThe process of removing Earth

materials from their original sites through weathering and transport agents or forces

Transport Agents or Forces include:• Water (Rain, streams, rivers, oceans, and

ice/glaciers)• Wind• Gravity

Stream Erosion and Deposition

Streams

Glaciers

Wind Transport of Dust

Wind Transport of Dust

GravitGravityy

Deposition Formations

Delta Formation from Deposition

Alluvial Fan from Deposition

REVIEWREVIEWWhat is the difference between

Weathering and Erosion?Weathering - processes at or near Earth’s

surface that cause rocks and minerals to break down by air, water, plants and animals

Erosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity

REVIEW- 2 Types of REVIEW- 2 Types of WeatheringWeathering

Mechanical/Physical Weathering - A rock is physically changed without a change in chemical composition

• Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break up

• Abrasion by wind and water Wearing down or smoothing of a material due to constant collisions

• Plant and Animal Action Plant root growth and animals burrowing increase the exposure of rocks to the air and water and causes breakdown

• Thermal Expansion and contraction Extreme changes in temperature causes cracking

• Pressure Unloading / Exfoliation Earth’s forces can push rock that formed deep underground up to the surface. The pressure causes the rock to expand and crack. This leads to exfoliation.

REVIEW -2 Types of REVIEW -2 Types of WeatheringWeathering

Chemical Weathering - Processes that change the chemical composition of rocks and minerals

• Hydrolysis Water is very slow reaction and the main cause of chemical weathering.

• Oxidation Where Oxygen combines with other substances to produce rust

• Acid Reactions / Carbonation Carbon reacts with other substances to dissolve and alter the chemical makeup of rocks forming caves. Nitric acid produced by the decay of organic material can alter soil composition

REVIEW (Continued)REVIEW (Continued)Differential Weathering - The variable rate of

which rocks weather is called differential weathering. Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years.

Factors affecting the rate of weathering include:• Composition (granite vs. limestone) What

minerals a rock is made from • Climate (hot, wet, cold, dry) hot, wet regions

weather rocks faster than cold, dry ones • Rock size (surface area) How large or small a

rock’s surface is