GEOL 100: Weathering and Erosion

Ugh

What is weathering?

The physical disintegration and or the chemical decomposition of rocks at the Earth’s surface that may result in the formation of sediments such as mud, sand, and gravel

What is erosion?

The physical removal and trasnport of sediment by water, wind, and ice

Differential weathering occurs how?

When different minerals in the same rock weather at different rates

What is mechanical weathering?

The physical breakdown of rocks and minerals

What is frost wedging?

It’s a type of mechanical weathering caused by the daily freeze-thaw cycle and the expansion and contraction of water

What is salt expansion?

It’s a type of mechanical weathering that occurs when water evaporates, allowing salt crystals to grow within the cracks and fractures in rocks

What is root wedging?

It’s a type of mechanical weathering that occurs when plant roots push rocks apart as they grow

What is pressure expansion?

It’s a type of mechanical weathering occurs when pressure is released from deeply buried rocks that are uplifted to the surface

Sheeting is what?

the formation of onion-like layers in granitic rocks due to pressure release and may result in Exfoliation Domes

• Eg.: Half Dome in Yosemite Valley

Sphereoidal Weathering results from?

Chemical weathering of the mechanically weathered joints and fractures in rocks 

Chemical weathering is what?

The chemical alteration or dissolving of minerals due primarily to acid water (i.e. Carbonic Acid - H2CO3)

What is oxidation?

It’s a type of chemical weathering that occurs when iron atoms bond with oxygen atoms to form iron oxide

• Eg:

  • Hematite, Geothite, Limonite

  • Laterite soil may form in wet climates 

What is hydrolysis?

a type of chemical weathering that occurs when silicate minerals (Eg. feldspar), are chemically altered to form Clay minerals 

What is dissolution?

It’s a type of chemical weathering that involves the dissolving of rocks and minerals by Carbonic Acid (H2CO3) also known as Acid Rain 

What is soil?

An unconsolidated combination of air, water, minerals, clay, and organic matter (i.e. humus), separating the biosphere from the geosphere 

What are Soil Horizons? What is a Horizon? What are its 5 layers?

1. well-formed soil with distinct layers

2. Loose organic material, including humus, at the Earth’s surface

3. 5 layers (this is their order):

   1. A horizon: also called topsoil, includes humus, mineral sediment, and some leaching of soluble minerals

   2. E horizon: a zone of leaching found in wet climates by downward percolation

   3. B horizon: also called subsoil, a zone of humus accumulation from upper horizons and chemically weathered sediment; the upper portion = regolith, lower = saprolite

   4. C horizon: a substratum and a zone of mechanical weathering with no organic material present

   5. R horizon: consists of unweathered, parent bedrock and fragments

How is soil classified (4; M, B, G, GS)?

By their morphology, behavior, genesis, and grain size

How many soil orders does the US’ Dep. of Agriculture recognize?

12 soil orders

What is Bauxite?

• (Al₂O₃)(H₂O)

• A mineral that forms when Laterite Soils are severely leached of silica and other soluble materials in a wet, tropical or subtropical climate

Bauxite is the primary ore of which metal (hint: also an element)

• Aluminum

  • Most of aluminum produced has been extracted from bauxite