Weathering:Processes of Change

EQ:

How does weathering occur?

Weathering • Describe three ways

abrasion occurs in nature.

• List three things that cause chemical weathering of rocks.

• Describe the similarity in the ways tree roots and ice mechanically weather rock.

• Describe five (5) sources of chemical weathering.

The Processes of Change

Lesson 18

Processes of Change (5)

• Weathering and erosion wear down, deposition fills in Earth’s surface.

• Weathering is the slow wearing away or breaking down of objects exposed to Earth’s atmosphere

• Two kinds of weathering act on Earth’s surface– Mechanical weathering– Chemical weathering

Weathering• Weathering is the process by which rock

materials are broken down by the action of physical or chemical processes.

• Mechanical weathering is the breakdown of rock into smaller pieces by physical means. (ice, wind, water, gravity, plants, animals)

• Chemical weathering is the process by which rocks break down as a result of chemical reactions. Water, weak acids, and air can cause chemical weathering.

Mechanical Weathering (4)

• When objects are broken down into small pieces but their chemical makeup doesn’t change

• Wind and moving water are two main causes of mechanical weathering

• Repeated changes in temperature (freeze, melt, freeze, melt again)

Chemical Weathering (5)

• Material of an object is changed

• Produces underground caverns

• Statue of Liberty needed repairs because of chemical weathering

• Examples:–Rust–Acid rain

Erosion (5)

• The natural moving of material from one place to another

• Erosion transports weathered rock material• Causes of Erosion:

– Moving water– Gravity– Wind– Glaciers (moving rivers of ice)– Waves

Deposition (5)

• Land torn down in one place is “deposited” in another place

• Gravity can cause a landslide moving mud, rock and soil down a hill

• Wind erosion can move sand and deposit it in another area

• Glaciers (rivers of ice) scrape rocks off the land and moves them downhill

• Glaciers will stop moving and even retreat and cut a steep U-shaped valley in the land

• Erosion caused by mountain rivers form V-shaped valleys

• Hurricanes create waves that erode beaches and cliffs

• Breaking of waves on a beach can wear it away. The larger the waves, the faster is the rate of erosion.

6 Agents of Mechanical Weathering

• 1. Ice – water seeps into cracks during warm weather. When the temperature drops, the water freezes and expands, causing the ice to push against the sides of the crack. This causes the crack in the rock to widen.– Abrasion – the grinding and wearing away of rock

surfaces through mechanical action of other rock or sand pebbles.

– The three ways that can cause abrasion are wind, water, and gravity.

Abrasion

• Abrasion – the grinding and wearing away of rock surfaces through mechanical action of other rock or sand pebbles. –The three ways that can cause

abrasion are wind, water, and gravity.

Three Causes of Abrasion• 2. Water – as rocks and pebbles roll along

the bottom of flowing water, they bump and scrape against each other, causing these rocks to become rounded and smooth.

• 3. Wind – wind blows sand and silt against exposed rock eventually wearing away the rock’s surface.

• 4. Gravity – rocks grind against each other during a rock slide, creating smaller and smaller rock fragments. Anytime one rock hits another rock, abrasion takes place.

Plants and Animals• 5. Some plants can easily break rocks. The

roots grow through existing cracks in rocks. The growth causes the root to expand, forcing the crack to widen. The force can eventually split the rock apart.

• 6. Animals that live in the soil (moles, prairie dogs, insects, worms, gophers), cause a lot of weathering. By burrowing in the ground, these living creatures brake up soil and loosen rocks to be exposed to further weathering.

3 Agents of Chemical Weathering

• Common agents of chemical weathering are water, weak acids, and air.

• These agents weaken the bonds between minerals grains of the rock.

• 1. Water – can cause rock to be broken down and dissolve. Can take thousands of years to take place.

• 2. Air – the process of oxidation is a chemical reaction in which an element (iron) combines with oxygen, causing rust.

• 3. Weak Acids - acid precipitation, acids in groundwater, acids in living things.

Three Sources of Weak Acids• Acid Precipitation – rain, sleet, or snow that

contains a high concentration of acid. Normal precipitation is acidic, acid precipitation contains more acid than normal.

• Acids in Groundwater – carbonic acid or sulfuric acid reacts with rocks in the ground, causing a chemical reaction, eating away at the rock.

• Acids in Living Things – Lichens produce acids that slowly break down rock.

Summary• Ice wedging is a form of mechanical weathering

in which water seeps into rock cracks and then freezes and expands.

• Wind, water, and gravity cause mechanical weathering by abrasion.

• Animals and plants cause mechanical weathering by turning the soil and breaking apart rocks.

• Water, acids, and air chemically weather rock by weakening the bonds between mineral grains of the rock.

Quick Check

Which of the following things cannot cause mechanical weathering?

• A. water• B. acid• C. wind• D. animals

Quick Check

Which of the following is a type of frost action?

• A. abrasion• B. oxidation• C. ice wedging• D. gravity

Quick Check

Which of the following types of chemical weathering causes a karst landscape, such as a cavern?

• A. lichens• B. acid precipitation• C. acids in groundwater• D. water

Quick Check

How do lichens slowly break down a rock?

• A. by abrasion• B. by mechanical means• C. by ice wedging• D. by chemical means

Quick Check

Which of the following will most likely experience oxidation?

• A. tennis ball• B. aluminum can• C. wooden fence• D. Bicycle tire

Quick Check1. The grinding and wearing away of

rock surfaces through the mechanical action of other rock or sand particles

2. Rain, sleet, or snow that contains a high concentration of acids

3. The process by which rocks break down as a result of chemical reactions

4. The breakdown of rock into smaller pieces by physical means

5. A chemical reaction in which an element, such as iron, combines with oxygen to form an oxide

6. The process by which rock materials are broken down by the action of physical or chemical processes

a. mechanical weathering

b. oxidation

c. weathering

d. acid precipitation

e. abrasion

f. chemical weathering