Weathering

Forces That Attack the Surface

Student Notes: To Print out your Notes.
Extra Credit: Complete all questions correctly for bonus points!
Mechanical Weathering Laboratory: Blocks and Smarties by Mr. Robison
Rates of Weathering Laboratory by Mr. Robison
Weathering Rates Laboratory by Drew Patrick

Standards: Major Understandings

2.1s Weathering is the physical and chemical breakdown of rocks at or near Earth's surface. Soils are the result of weathering and biological activity over long periods of time. Mass Movement: Earth materials move down-slope under the influence of gravity.

2.1t Natural agents of erosion, generally driven by gravity, remove, transport, and deposit weathered rock particles. Each agent of erosion produces distinctive changes in the material that it transports and creates characteristic surface features and land-scapes. In certain erosional situations, loss of property, personal injury, and loss of life can be reduced by effective emergency preparedness.

What's up with this rock?

1. Ice wedging (Frost Action): Water seeps into small cracks and expands as it freezes breaking the rock. Very strong force. ex: potholes, ice heaving.

Ice Wedging is the main weathering force on mountain tops

2. Abrasion: Rocks rub or collide against one another.
ex: wind blown particles colliding, pebbles tumbling downstream, glaciers grinding rocks together.

3. Exfoliation: (Pressure Release): breaking of rocks off mountains in large shells creating rounded mountain peaks.

When pressure is released rocks expand and crack peeling off in sheets.

1. Oxidation: Exposure to oxygen rusts the iron minerals in rocks and makes iron-oxide (rust).

Oxygen, in the air we breathe, reacts with iron in minerals to form iron oxide minerals, e.g. hematite (rust). Many minerals contain iron, so it is not unusual to see red-colored rocks like the example shown here.

2. Hydrolysis: Feldspar, hornblende, and augite when exposed to water form clay.

3. Carbonic Acid: Carbon dioxide from decaying organic material mixes with water forming carbonated water. This water is slightly acidic and dissolves away the minerals like calcite changing the original mineral into a clay mineral. Produces caves and karst topography.

(Cave Formation!) (sinkholes: turn to page 162 in textbook).
Carbonic acid dissolves limestone as it filters down through the cracks in layers of rock. When it reaches the caverns, the carbon dioxide escapes from the water and leaves some of the dissolved limestone in the form of calcite first on the ceiling. This builds up to form stalactites. The water then drips off the end of the stalactite onto the floor below where it builds up to form stalagmites. What is left runs down the wall to form flowstone. It takes about 100 years to form one cubic inch of calcite. it's easy to remember the difference between stalactites and stalagmites. The word "stalactites" contains the letter "c" - like the word "ceiling." "Stalagmite" uses the letter "g" and so does the word "ground." Stalactites grow from cavern ceilings, while stalagmites grow upward from the ground!
Check out a typical cave and its wonders.
- Check out the Howe Caverns!
- Also check out the Carlsbad Caverns!
- Or how about the Virtual Cave!
- Sometimes caves collapse creating karst topography!
- Collapsing caves create sinkholes and lakes on the earth's surface.
  - Florida karst topography
  - How would like this in-ground pool?

4. Acid Rain: Carbon dioxide and Sulfur combine with water in the air to form acid rain

Name two types of rocks that erode faster because of acid rain.

___________________________
___________________________

Factors of Weathering:

1. Climate: Average weather conditions in an area. Most important factor affecting weathering.

Hot, wet climate = Strong Chemical weathering.

Cold, wet climate = Strong Mechanical weathering.

Dry Climate	Wet Climate

2. Hardness of Bedrock: Harder rocks will weather slower than softer rocks (p.178).

The Hard caprock of dolostone makes the Falls water fall!
Why is the Canadian falls is curved like a horseshoe?

Ans. The undermining of rock at the falls occurs because of the softer shale is eroding faster than the overlying limestone.

3. Surface Area exposed: When a big rock is broken into smaller rocks there is more surface area and therefore more exposure for weathering. The more weathered a rock is the faster it weathers.

Smaller pieces = more surface area = faster weathering

Soil Formation:

Regolith is composed of rock and mineral fragments
produced by weathering.
If this material is transported by wind, water, or ice it is termed sediment.
Soil is that portion of the regolith that supports plant life and includes organic material, water and air.

A soil profile is a cross-section of the earth exposed by digging. In mature soil profiles there are three distinct zones or horizons.

A-horizon: Topsoil-darker soil because it contains organic material, or humus which forms from decayed plant material

B-horizon: Subsoil-red to brown color because it contains more clay and iron oxides that were washed down from the topsoil.

C-horizon: slightly weathered parent material such as rock fragments. This horizon is on top of bedrock.

Residual Sediment – Soil made from the bedrock beneath.

Transported Sediment - weathered particles that have been moved a great distance from their parent rock. ex. if you found an igneous rock near here, we can assume that it is transported sediment.
Note: Transported sediments tend to be more rounded due to abrasion with other sediments and its surroundings during transport.

Why should we assume that much of our sediment has been transported?