Thursday, March 3, 2011

Chemical and Mechanical Weathering and of Red Rocks

"Weathering is the breakdown and alteration of rocks and minerals at or near the Earth's surface into products that are more in equilibrium with the conditions found in this environment. Most rocks and minerals are formed deep within the Earth's crust where temperatures and pressures differ greatly from the surface. Because the physical and chemical nature of materials formed in the Earth's interior are characteristically in disequilibrium with conditions occurring on the surface. Because of this disequilibrium, these materials are easily attacked, decomposed, and eroded by various chemical and physical surface processes." From

The three types of weathering are chemical, physical and Biological, I am going to cover only  chemical and physical or mechanical weathering in this post.

Chemical weathering occurs when the composition of rocks change,  and the process of a rock changes take place below ground surface where water and rocks are in contact in the soil. There are two common minerals, halite and calcite and they are "often found in water and are able to dissolve rocks. When oxygen combines with iron-bearing silicate, the rock can begin to "rust." However, gases and other solutions can also chemically alter rocks (pollution in cities demonstrates this well)." 

The photos are from the Red Rocks Trading Post

Chemical weathering of rocks

Mechanical or physical weathering is the breakdown of  rocks without chemically  causing any changes. It occurs "when a rock changes form, but not its elemental make up."

The photos are from the Red Rocks Trading Post
                                                    IMG Photo
according to, mechanical weathering:
  1. Expansion and Contraction - the thermal heating and cooling of rocks causing expansion and contraction

  2. Frost Action - Water freezes at night and expands because the solid occupies greater volume. Action wedges the rocks apart. Requires adequate supply of moisture; moisture must be able to enter rock or soil; and temperature must move back and forth over freezing point.

  3. Exfoliation - process in which curved plates of rock are stripped from a larger rock mass. Example Half Dome. Exact mechanism uncertain but probably due to unloading.

  4. Other types - Cracking of rocks by plant roots and burrowing animals.
                                          IMG Photos

1 comment:

  1. As I was reading your blog I kept thinking how much I want to go to Red Rocks! I enjoyed your in-depth explanation of chemical weathering. Your detailed description of the process actually helped further explain to me how weathering works. I liked the pictures, especially the last one but I thought there could be more variation. Perhaps Red Rocks at a different time of day? Overall, I thought you presented the material in a clean and organized manner.