Breaking it Down

Weathering & Erosion

4/30/15

Breaking it Down

Key Question: What is weathering, and what are some examples?

Initial Thoughts:

Evidence: Weathering

• Large rocks and landforms first need to be broken down into smaller pieces in order to be worn away by erosion.

• This is accomplished by weathering - the breaking down of rock by chemical or mechanical processes

Mechanical WeatheringDefinition: Breaking up of rock by physical

forces, such as the action of wind and moving water.

The rock itself does not change; it just gets broken into smaller pieces.

Process Name Where does it occur?

What is it?

Frost Wedging

• Go to the website, which can be found on my links page under “Mechanical Weathering, and click “NEXT” twice: http://ees.as.uky.edu/sites/default/files/elearning/module07swf.swf

Check yourselfProcess Name Where does it occur? What is it?

Frost Wedging Cold, moist mountains Water expands when it freezes, breaking apart rocks

Exfoliation Mountains with igneous rock

Igneous rock pushes up, breaking off big sheets of rock

Thermal expansion

Desert regions Crystals in rocks expand & contract with extreme temperature changes, weakening & breaking the rock.

Crystal Growth Coastal & desert regions Salt crystals grow and weaken & loosen rocks

Tree roots Warm, moist regions that support forests

Tree roots wedge into rocks and break them apart

Abrasion Wherever there’s water, wind, or ice

Rocks falling and breaking or wearing down by the direct actions of other rocks

http://en.wikipedia.org/wiki/Image:Weathering_freeze_thaw_action_iceland.jpg

Exfoliation or unloading - rock breaks off into leaves or sheets along joints which parallel the ground surface; caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial

Organic activity (TREES/root-pry, burrowing animals, human activities)

Abrasion & Gravity: rocks falling and colliding with other rocks

Contraction due to crystallization

The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallisation. This example is at Yehliu, Taiwan.

Salt weathering of building

stone on the island of Gozo, Malta

Chemical Weathering

Definition: wearing away of rocks by chemical processes, such as dissolving or oxidation.

• It’s a breaking down process

Chemical Weathering

Process Name Where does it occur?

What is it?

Dissolution

Oxidation

Hydrolysis

• Acids or water dissolve the rocks.• Sources: Acid rain from pollution, plant roots,

water & limestone (example caves),

Water: Dissolves minerals out of rocks making them weaker

Dissolving

Acid: Dissolves minerals in rocks examples: carbonic acid, acid rain, and plant acid

Chemical weathering

Lichens such as these growing on the rocks in the picture can produce weak acids that react with the rock.

3000 year old Egyptian Obelisk 3000 year old Egyptian Obelisk after 100 years in NY

Oxidation

• Oxidation or rusting - some minerals contain metals, like Iron or sulphur, that can rust when exposed to oxygen. Just like an old car, nail, or piece of metal left outside.

Oxidation

Evidence 2: Weathering LabEach group will be assigned two of the 8

treatment groups:

1. Crushed tablet in water

1. Whole tablet in water

2. Crushed tablet in heated water

2. Whole tablet in heated water

3. Crushed tablet in vinegar

3. Whole tablet in vinegar

4. Crushed tablet in heated vinegar

4. Whole tablet in heated vinegar

Analysis Q’s1. Compare & contrast mechanical and

chemical weathering. (a venn diagram or chart is o.k.)

2. Which of the treatment groups in the lab represented mechanical weathering?

3. Why do you think the obelisk (slide 17) showed more weathering during the 100 years in New York than it did in the 3,000 years it was in the desert in Egypt?

SummaryWhat did you think about how weathering

works before this lesson?

What did you learn about how weathering works from this lesson? (Minimum of 3 sentences!!!)

What are some further thoughts or questions you have about how weathering works?

Reflection

• Explain how mechanical and chemical weathering are similar to the process of mechanical & chemical digestion. Use words, pictures, or both.

Big Idea

• Rock landforms can be broken down by the natural processes of mechanical & chemical weathering.