Weathering and Erosion

Weathering is the breakdown and alteration of earth-forming materials by low pressure, temperature, water, air, and biological organisms.

Weathering

Weathering happens quicker on newly exposed rock because the minerals have not met their equilibrium state with their environment.

Weathering

Weathering surface are changed in color, texture, composition, firmness or form, with little or no transportation of the altered material

Weathering

Weathering is responsible for soil formation, nutrients used by marine organisms, fossil fuels and sedimentary ore deposits.

Weathering

Erosion is the transportation and removal of material produced by weathering.

Erosion

Erosion is caused by wind, water, currents, glaciers, humans, and animals.

Erosion

This type of weathering involves breaking down rocks into progressively smaller pieces.

It increases the surface area exposed to the elements to increase the rate of chemical weathering.

Physical or Mechanical Weathering

1. Pressure or Stress Release (Unloading)◦ The removal of surface material by water,

glacial erosion or human activities that could cause the minerals in the rock to spread further apart to create large voids.

Types of Mechanical Weathering

2. Frost Action◦ The changes in pressure caused by the cycle of

freezing and thawing of water in colder climates in joints and crevasses may cause the rocks to fracture.

Types of Mechanical Weathering

3. Salt Weathering◦ The salt penetrates the rock’s surface and

embeds itself in the pores and small cavities in the rock.

◦ The salt change size by either absorbing water or when the temperature changes.

Types of Mechanical Weathering

4. Heating and Cooling (Exfoliation)◦ Rock is also a poor conductor of heat so the

surface may be hot, but the interior might be cold. This difference in temperature may can the rock to break apart.

Types of Mechanical Weathering

Minerals in a rock undergo changes that make them more stable under their current environmental and biological conditions.

Chemical Weathering

1. Water◦ Water serves as a medium for any chemical

reaction to occur between a rock’s environment and it’s minerals. Flowing water prevents the chemical reaction to reach a state of equilibrium, thus allows it to continue indefinitely.

Causes of Chemical Weathering

2. Chemical Reactions◦ the reaction between the ions in the water and

the minerals. This decomposes igneous rock.

Causes of Chemical Weathering

Hydrolysis

Ion Exchange

Oxidation

Carbonation

The type of weathering that is the result of biochemical or biophysical processes associated with living matter.

Biological Weathering

Worms increase a surface’s exposure to air and water.

Biological Weathering

Bacteria break down chemicals and minerals and produce harmful by-products.

Biological Weathering

Algae, lichen and fungus colonize rock surfaces reducing their contact with water and air and create ions that react chemically with the surface.

Biological Weathering

P. 161 #1-4 P. 166 #1-4

Homework