Weathering and Soil

1. Weathering and Soil

2. Weathering • Effects – surface processes break down rock into small pieces called sediment.

3. Mechanical Weathering • Physical processes break rocks into fragments with the same chemical makeup and characteristics as the original rock. • Plant roots and burrowing animals cause mechanical weathering • Ice wedging – water enters cracks and freezes and expands, breaking rocks apart. • Small pieces of rock have more surface area than larger pieces of rock and weather faster.

4. Chemical Weathering • Chemical reactions dissolve minerals in rocks or change them into different minerals. • Carbonic acid, formed from carbon dioxide gas and water, and plant acids can react with minerals to weather rock. • Oxidation – chemical process that occurs when iron is exposed to oxygen in the air.

5. Effects of Climate – pattern of weather that occurs over time. • Mechanical weathering is more rapid than chemical weathering in cold climates. • Chemical weathering is more rapid than mechanical weathering in warm, wet climates. • Rock type can affect rates of weathering.

6. Formation of soil • Can take thousands of years • Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air. • Formation is influenced by climate, slope, types of vegetation, and length of time that rock has been weathering.

7. Soil Profile • Make up of different layers of soil • 1. Horizon A – top soil layer • May be covered with organic litter that may turn into humus • Fertile layer with more humus and less rock and mineral particles than other soil horizons • 2. Horizon B – middle soil layer • Contains less humus and is lighter in color than A horizon • Minerals travel from A horizon to B horizon in a process called leaching

8. Horizon C • Bottom soil layer • Has very little organic matter and is not strongly affected by leaching • Contains rock – the parent material of the soil • Glaciers can deposit soil that did not form from the bedrock beneath it.

9. Soil Types • Differ in different places • Different regions have different climates that affect soil development • Parent rock affects soil formation and type of vegetation that grows in a region • Time affects soil development because the longer the weathering has occurred, the less the soil resembles the parent rock. • Soil on steep slopes develops poorly

10. Soil Erosion • Soil erosion or loss is important because plants do not grow as well when topsoil is lost.

11. Causes and effects of soil erosion • Many human activities disturb the natural balance between soil production and soil erosion. • Agricultural cultivation – Increased farming removes the plant cover, leaving soils open to wind and water erosion • Forest harvesting – removes forest vegetation which increases erosion and particularly damages tropical rain forest soil • Overgrazing results when animals graze until almost all ground cover disappears. • Urban construction clears land of vegetation and removes soil

12. Links • Enchanted learning • Animation of soil layers • http://courses.soil.ncsu.edu/resources/soil_classification_genesis/soil_formation/soil_transform.swf • Animation