GL 107 Earth Systems Science
K. Hannula
Discussion questions for 10/15/07
1. How do the following factors control the type of soil that is found in a given area?
Time: Chemical weathering takes a long time. The longer rock has been exposed at the surface, the more developed the soil will be.
Climate: Warm climates favor faster chemical weathering, and the formation of soils that contain a lot of iron oxides and clays. Water is also necessary for both chemical and mechanical weathering. Extremely dry climates tend to have very thin soils. In climates that are both wet and hot, soluble elements (K, Na, Ca, Mg) tend to be leached out of the soil.
Plants and animals: Decaying material contributes humus to soil. It also contributes carbonic acid to help chemical weathering continue.
Slope: Weathered material is rapidly eroded from steep slopes, so soils do not have time to develop as completely on steep slopes.
2. Define:
leaching: The removal of soluble ions (such as Na+, K+, Ca2+, Mg2+) from soils by water flowing through the soil.
laterite: A tropical soil, dominated by the presence of iron oxides and clay minerals. Many nutrients have been removed from laterite soils by leaching.
3. What are the characteristics of the soils formed in each of the following climate zones, and why are those particular soils found in those places? See Table 3.2, p. 81 in textbook.
temperate humid: light-colored, acidic topsoil; subsoil enriched in aluminum, iron, clay. Water contributes to chemical weathering, but temperature too low for the extreme weathering found in the tropics
temperate dry: calcite precipitates due to evaporation of water; hard calcite-rich layer called "caliche" is formed
tropical: laterite soils, with lots of iron oxides and aluminum (from extreme weathering of clays); everything else, including important nutrients, is removed by leaching
extreme arctic or desert: extremely slow weathering results in thin, weakly-developed soil
4. What factors increase the likelihood of mass wasting?
steep slopes
saturation of soil or rock with water
removal of vegetation
added weight to slope
cracks or other planes of weakness in rock sloping same direction as hillside