Physical (Mechanical) and Chemical Weathering Created By: Mr. Kreeger

Page References and Homework Do problems # 1a,b and c, 2a, 3a,b and c, 5a Do problems # 2b, 5b,c and d Do problem # 6

Table of Contents Weathering Defined Types of Physical Weathering Frost Wedging Abrasion Wetting and drying Exfoliation Plant roots Lichen and moss Types of Chemical Weathering Oxidation Hydrolysis Carbonic Acid Factors affecting Weathering Hardness Surface area Climate

Introduction Video Clip Weathering

Weathering Defined Breakdown of rocks into smaller particles by natural processes Exposure to air, water and living things at or near the surface results in weathering Two Types Mechanical Weathering Chemical Weathering

Physical (Mechanical) Weathering Video Clip

1. Types of Physical (Mechanical) Weathering Physical (Mechanical) Weathering- The breakdown of rocks w/out changing chemical compositions a. Frost Wedging- Water enters crack Freezes  Expands Forces crack to open wider (Process repeats until rock splits)

Eventually, the rock splits from repeated frost action!

1. Types of (Physical) Mechanical Weathering cont… Abrasion- Process of rocks rubbing against each other Occurs where fragments of rocks are carried along by streams Breaks rocks into smaller pieces and makes them more rounded. Wind also weathers rock by abrasion. (Think about the beach)

1. Types of (Physical) Mechanical Weathering cont… c. Wetting and drying breaks up rocks that are made from clay When they are wet they expand, and they shrink as they dry As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!

1. Types of (Physical) Mechanical Weathering cont… d. Exfoliation soil and rock is removed (glaciers or uplifting), exposing rock found deep underground This releases the pressure causing the surface of the rock to expand and eventually crack

1. Types of (Physical) Mechanical Weathering cont… e. Plant Roots The deep roots of trees often break apart rocks f. Lichen & Moss These low to the ground plants can grow on rocks and eventually break them apart

Introduction Clip to Chemical Weathering

2. Types of Chemical Weathering Chemical Weathering- The breakdown of rocks by changing their chemical compositions. (The presence of oxygen, water and Carbon Dioxide is most responsible) a. Oxidation- Oxygen reacts with many minerals especially those containing iron to form rust. (Occurs faster with water)

Chemical weathering of basalt

Iron Banding in Basalt

Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)

Video Clip about Oxidation

2. Types of Chemical Weathering cont… b. Hydrolysis water (hydro) reacts with minerals such as feldspar and form clay

2. Types of Chemical Weathering cont… c. Carbonic acid carbon dioxide (CO²) dissolves in water to form this acid can cause minerals to dissolve, especially those containing calcite

“Gnarled Rock” – a formation of limestone chemically weathered by acid rain

3. Factors affecting the rate of weathering Rocks resistance to weathering (Hardness) Amount of surface area Climate

3. Factors affecting the rate of weathering cont.. Hardness and mineral composition- Limestone's most affected while granite is least affected.

The central area of rock was less resistant to weathering…thus the “arch” was formed!

3. Factors affecting the rate of weathering cont.. Surface Area Surface area is the amount of rock surfaces exposed to the atmosphere Greater surface area increases the rate of weathering Weathering creates more surface area

3. Factors affecting the rate of weathering cont.. Climate The temperature and moisture levels in an area over a long period of time. Cold and Moist- Best for Physical Weathering Warm and Moist- Best for Chemical Weathering

Dry Climate = Mechanical Weathering! Devil’s Marbles, Australia – Mechanical weathering from wind and sand!

Warm Climate = Chemical Weathering Parthenon – Athens, Greece

Video Clip of Humans Impact of Weathering