Soil

1. Soil

2. Benchmark(s) • Explain how rocks are broken down, how soil is formed, and how surface features change.

3. Introduction Video

4. Weathering • Weathering is the term used to describe the breaking of rocks into smaller fragments. There are two types of weathering • 1.  physical and • 2.  chemical.

5. Physical Weathering • Physical weathering is weathering that breaks apart rocks without changing their chemical composition. Water, wind, or gravity are usually responsible for physical weathering.

6. Chemical Weathering • Chemical weathering occurs when water, air, and other substances react with the minerals in rocks. An example of chemical weathering is when the acids in rainwater dissolve away rocks. Water is the main cause of chemical weathering. Chemical weathering is most rapid in regions with much moisture and warm temperatures.

7. When we look at a landscape, we usually see grass, plants, and trees. Without soil these would not exist. Soil is a complex mixture of fresh and eroded rocky material, dissolved and redeposited minerals, and the remains of once living things.

8. These components are mixed together by the burrowing of animals, the pressure of plant roots, and the movement of water underground.

9. The type of soil, its chemical composition, and the nature of its organic origin are all important to agriculture. • Many different types of soils exist. • Soils vary depending on the climate. • Soil is formed in a number of layers. • Their sequence is called the soil profile. • The layers, also called horizons, show the different things that go into making a soil-from the decay of rocks to the addition of material from living things.

10. Not all soils have the same horizons, and their sizes vary from soil to soil. • There are generally five horizons.

11. Soil Horizons • Horizon 0 is the humus layer that contains deposits of plant material. Horizon A is the topsoil.This is organically rich, but some minerals are taken out by groundwater. • Horizon B, the subsoil, is less organic, but is rich in minerals brought down from the topsoil. • Horizon C, the parent rock, is broken and weathered into loose chunks, and contains no organic material. • Horizon D is the underlying bedrock. The mineral content of the soil comes from this.

12. Erosion • Erosion is the process that moves weathered sediments from one location to another. The four major agents of erosion are gravity, running water, glaciers, and wind.

13. Rainwater falls to form pools of water or sinks into the soil and re-emerges as springs. • This water is channeled into valleys and hollows, eventually forming the streams and rivers that flow down to the sea. • Flowing water helps shape the landscape. It wears away the rocks of the mountains, again depositing the debris on the plains and lowlands, and eventually the floor of the sea.

14. Erosion • Erosion is the process that moves weathered sediments from one location to another. • The four major agents of erosion are gravity, running water, glaciers, and wind. • When gravity alone causes material to move, its called mass movement. • Some mass movements are very slow; other types happen very quickly. • Some different types of mass movements are slumps, creeps, rockslides, and mudflows

15. Water Erosion • Water erodes more sediments than any other agent of erosion. Water erosion can be classified into rill erosion, gully erosion, and sheet erosion. Rill erosion begins when a small stream forms during a heavy rain.

16. Gulley Erosion

17. Rill Erosion • If a stream frequently flows in the same path, rill erosion may evolve into a gully erosion.

18. Sheet Erosion • When rainwater flows into lower elevations and carries sediments with it.

19. Glaciers • A moving mass of ice and snow is a glacier. • A glacier is an accumulation of ice, air, water, and rock debris or sediment. • It is a large enough quantity of ice to flow with gravity due to its own mass. • Glaciers flow very slowly, from tens of meters to thousands of meters per year (tens of feet to thousands of feet per year).

20. Glaciers • The ice can be as large as a continent, such as the ice sheet covering Antarctica.

21. Continental Glacier • There are two types of glaciers: continental glaciers and valley glaciers. Continental glaciers are huge masses of ice and snow found near Earth's polar regions.

22. Valley Glaciers • Valley glaciers are located in mountainous areas where the average temperature is low enough that snow does not melt over the summer season.

23. Regions in Michigan where erosion by wind, water, or glaciers have occurred: • river valleys • gullies • shoreline of Great Lakes • along the shoulders of roads • under downspouts • chemical weathering from acid rain • formation of caves • sinkholes

24. Physical weathering from frost action: • potholes • cracks in sidewalks

25. Physical and chemical weathering by: • bacteria • fungi • worms • rodents • other animals