PG. 69

Weathering

Weathering

The process by which rocks on or near Earth’s surface break down and change

The removal and transport to other locations is erosion

Types of Weathering

Mechanical – by physical processes Only changes the shape and size

Chemical – Changes the chemical composition of the rock

Mechanical Weathering

Mechanical weathering is affected by: Temperature-

Water freezes in rocks and causes them to expand and then contract eventually causing cracks (Frost Wedging)

Causes potholes Pressure-

overlying rock is carried away, lower rock layers expand and create cracks known as joints

when outer rock layers are stripped away it is called exfoliation

Chemical Weathering

Agents of chemical weathering: Water

Can dissolve many rocks and minerals Reaction of water with other substances called hydrolysis

Oxygen Chemical reaction of oxygen w/ other substances called

oxidation Carbon dioxide

When combined w/ water, produces carbonic acid Acids

Acid rain can degrade rocks (caused by sulfur dioxide and nitrogen oxides we put into the air)

Use pH to determine the acidity (the lower the more acidic) 5.6 is the pH of normal rainfall

Rate of weathering

Weathering occurs very slowly (2000 yrs to weather 1 cm of limestone)

Climate can influence the rate of erosion Amount of rainfall, temperature, and evaporation Chemical weathering occurs more in warmer wet climates (lots of

organic material in soil that eventually produces carbonic acid) Mechanical weathering occurs more in cooler dry climates

Rock Type Sedimentary rocks more easily broken down

Surface area The smaller the pieces, the more surface area, the more chemical

weatheringTopography

Materials on slope undergo weathering more readily

QuestionsPg. 70

Answer numbers 1-4 on page 161Write both the question and answer

Questions

1. Distinguish between weathering and erosion.2. List several variables that affect the rate of

weathering.3. What two climatic factors are most important in

the weathering process?4. Describe how one variable may affect another

variable in the weathering process (i.e. how mechanical weathering can affect chemical weathering).

5. make a graph that would represent the relationship between the rate of weathering and the surface area of material.