Weathering and ErosionWeathering and Erosion

DefinitionDefinition

• Weathering and Erosion are the processes that sculpt and mold the surface features of the earth

• There is a constant conflict between forces that cut down the surface and forces that raise the surface

WeatheringWeathering

• The breakdown of material – By air, water, plants, and animals

ErosionErosion

• Movement or transport of that weathered material

2 Types of Weathering2 Types of Weathering

• Physical Weathering– Mechanical breakdown without chemical

change• Abrasions• Ice Wedging• Exfoliation

AbrasionsAbrasions

• Wearing down or smoothing of a material due to constant collisions– Beach glass, sand

blasting

PHYSICAL WEATHERING - PHYSICAL WEATHERING - ABRASIONABRASION

ROCK PARTICLES GRIND AGAINST ONE ANOTHER

WATER WIND

Ice Wedging (Frost Action)Ice Wedging (Frost Action)

• Break up due to repeated freezing and thawing– Pot holes

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

ExfoliationExfoliation

• Peeling away of surface layers, caused by changes in Temperature and pressure or vegetation (trees, grass, vegetation growing on rocks.)

• Roots wedge into pores and cracks, splitting the rock

PHYSICAL WEATHERING – PHYSICAL WEATHERING – ROOT ACTIONROOT ACTION

PLANT ROOTS UPLIFT AND FRACTURE ROCK

PHYSICAL WEATHERING - PHYSICAL WEATHERING - EXFOLIATIONEXFOLIATION

Sand is the remains of weathered and eroded rock!

Chemical WeatheringChemical Weathering

• Rock broken down by chemical action, changes the compostion of rock (O2, H2O, CO2)

OxidationOxidation

• When O2 chemically unites with minerals– O2 and Fe (iron) form FeO2 (iron oxide or rust)

HydrationHydration

• H2O chemically unites with minerals– Feldspar and Hornblade plus H2O makes clay.

CarbonationCarbonation

• CO2 chemically unites with minerals– CO2 + H2O = weak

carbonic acid (acid rain)

– Carbonic acid dissolves limestone creating caves

CARBONATIONCARBONATION

Stalagmites and stalactites

WHAT KIND OF CLIMATE WHAT KIND OF CLIMATE SUPPORTS WEATHERING?SUPPORTS WEATHERING?

COLD →→→→→→→→→→ HOT

HIGH

PPT

↑

↑

↑

↑

↑

↑

↑

LOW

PPT

How does climate affect How does climate affect weathering?weathering?

• Physical Weathering– Works better in a cool

and dry climate

• Chemical Weathering– Works better in a hot

and moist environment– More water = more

weathering

WHICH DIAGRAM IS AN ARID WHICH DIAGRAM IS AN ARID CLIMATE? HUMID CLIMATE?CLIMATE? HUMID CLIMATE?

A B

Humid – more rounded

Arid – more angular

Weathering RatesWeathering Rates

• Note to everyone!– Time is a relative thing, when we talk about

time in geology, we must remember that the earth has been around four billions of years!

– 100 years compared to 1,000,000,000 is very small!

Weathering RatesWeathering Rates

• Climate– Dictates temperature and amount of moisture– #1 factor in weathering process

Weathering RatesWeathering Rates

• Surface area exposure– More surface area = greater weathering

– Which will weatherThe fastest?

PHYSICAL WEATHERINGPHYSICAL WEATHERING INCREASES SURFACE AREA

MORE CHEMICAL WEATHERING CAN OCCUR

Surface AreaSurface Area

• Which will weather faster, solid rock or crushed rock

• The crushed rock of course!– The large rock is tightly packed and has less

surface area exposed– The crushed rock is loosely packed and has

more exposed.

Mineral CompositionMineral Composition

• The harder the rock, the slower the rate of weathering is

• Composition dictates hardness which determines resistance to weathering.

WHICH LAYER IS MORE WHICH LAYER IS MORE RESISTANT TO WEATHERING?RESISTANT TO WEATHERING?

LEAST RESISTANT?LEAST RESISTANT?

A

BC

D

SoilSoil

• One of the major products of weathering is soil

Residual SoilResidual Soil

• Forms from the weathering of the underlying bedrock

Transported SoilTransported Soil

• Different in composition from underlying bedrock.– Ex. Long Island soil

• It takes hundreds of years for soil to form– Average is 2.5cm3 per year

• What type of soil do we walk around on?– Most soils are transported

TRANSPORTED SOILS DUE TO …TRANSPORTED SOILS DUE TO …

Welcome to Huntington Cemetery! Step inside to another real-life weathering laboratory!

Wow! We haven’t even stepped inside and we have evidence of weathering in the gate!

What process is this and is it physical or chemical?

We are going to look at cemetery rocks…(tombstones!) and observe the weathering that has occurred in them.

Since tombstones are dated we can even determine how long the weathering has occurred!

Here is a typical marble tombstone which used to be a very popular rock for cemeteries.What mineral largely composes the rock marble?

What is the hardness of this mineral? Why was it a good rock for tombstones?

Here is another type of tombstone. It is made up of slate.

Compare the two tombstones in the next picture. How do they differ in terms of the types of weathering that has occurred to each?How do they compare in appearance? Which appears more weathered?

Marble Slate

Marble Slate

Which tombstone is older?

Marble Slate

This means that rocks can weather at different rates!

This is called “Differential Weathering”

Rocks weather at different rates due to differences in mineral composition.Some minerals are more stable at the earth’s surface than others! These take longer to weather.

Calcite is very unstable at the earth’s surface in certain climate types. Which type in particular?

What weathering process causes the tombstones to “dissolve”? Is this chemical or physical?

CO2 CO2