AIM: What is Weathering?

Do Now – Choose one of the following pictures and describe what is/has

happened.

I. Weathering the breaking down of a rock into

small pieces.

As Surface area increases the amount ofWeathering increases

II. Mechanical (Physical) Weathering

- changing the size and shape of the rock.

Abrasion:

rocks hitting and smashing against each other.

III. Types of Mechanical Weatheringa) Frost Wedging

Do Not Copy

the expansion of frozen water in cracks of rockscause it to break.-This broken material is called talus

What happens to water when it freezes?

b) Biological Activity -

organisms, plants, burrowing animals, and humans break down rocks.

IV. Chemical Weathering

changing the rocks chemical composition.

- forms a new material.

* Water is the most important agent.*

Acid Rain Damage

Soluble:

a material that can be dissolved by water.

V. Types of chemical weathering

a) Acid Rain

- water combines with different elements to make acids.

- this is known as Hydrolysis.

- H2O + carbon dioxide = carbonic acid

* - H2O + sulfur = sulfuric acid (acid rain)What material will all these acids react

with?

Do Not Copy

•Acid rain reacts with calcite and dolomite in the rocks (Limestone).

•This dissolves the rock creating Karst Topography (caves), stalactites and stalagmites.

b) Oxidation

- Water and oxygen react with metal to create rust.

VI. Rate of Weathering

A) Rock Characteristics:

- Mineral composition and solubility of the rock (the minerals that make the rock) determine the rate of weathering.

Granite Limestone

- amount of surface area determines amount of weathering

- Some rocks are more resistant (harder) to weathering. Mineral composition is the greatest determining factor.

Hoodoo

In the diagram below, which letter rock is most resistant

to weathering?

B) Climate:

- Temperature and moisture are the most crucial factors.

- Chemical weathering is most effective in areas with high temperatures (heat)

and abundant moisture (water).

Explain the difference in weathering of the two headstones (roughly the same age). What

caused the difference in weathering?

Slate Headstone Marble Headstone

Closure: In your Notes

Cleopatra’s Needle

1900 - EgyptPresent Day -Central Park

2) Describe one factor that

explains why Cleopatra’s

needle changed after it was

brought from Egypt to New

York.