Chapter 12: Weathering

1. Chapter 12: Weathering

2. Chapter 12.1

3. Weathering – The breakup of rock due to exposure to process that occur on Earth’s surface.

4. Mechanical Weathering - (disintegration) the breakdown of rock into smaller pieces (no change in composition) • Frost wedging occurs when water gets into cracks of the rock and freezes when freezing water occupies 10% more space. • Bare mountaintops are very susceptible forming large sharp cornered boulder fields below • Pavement potholes are also caused by frost wedging

5. Abrasion – caused by water wind and ice scraping rocks, sand and pebbles against one another. • Plants and animals • Roots grow and split rock • Animals make holes • Upward Expansion • Exfoliation – the release of pressure from overlying rocks causes rocks underneath to expand upward and crack.

6. Chemical weathering – (decomposition) • Takes place when the rock’s minerals are chemically changed into something different. Usually caused by water or water vapor

7. Hydrolysis – reaction of water with other substances • Usually increased in effect due to an acid in the water • Carbonic acid – rainwater with CO2 has the greatest effect on calcite (limestone) forming underground caverns. • Acid rain – sulfur dioxide, nitrogen and carbon dioxide released by industries react with water in the air.

8. Oxidation - oxygen with other substances • Oxygen and iron will form a red iron oxide called hematite

9. Rates of Weathering • The more the rock is broken down the faster it weathers due to more surface area exposed to water. • Composition of the rock • Sandstone with a silica (quartz) cement is more durable than one with a calcite cement • Climate – a warm wet environment is more conductive to both chemical and mechanical weathering

10. Chapter 12.2

11. Soil – is made of loose weathered rock material with organic matter (dead stuff)

12. How soil forms • Parent material – what the soil came from • Residual – from the under laying rock • Transported - brought in by rivers glaciers or wind and deposited in the area. • Soil Profile – how the soil is layered in 3 distinct zones • A horizon – usually dark to light gray (topsoil) • B horizon – often red to brown (subsoil) • C horizon – partially weathered bedrock

13. Soil Composition – most important factor is climate p.266 in book. Tropical forest soil – has a very deep soil profile because of the warm wet region it forms in.

14. Chapter 12.3

15. Mass Movement (The downward transportation of weathered material by gravity) • Erosion (the removal and transport of material by natural agents)

16. Types of Mass Movements • Loose rock material continually moving downhill after it has been weathered. May form a talus pile at the base of a steep hill or mountain a talus pile can have a 40° slope. • Landslide - movement of bedrock and soil down slope. • Creep – a very slow down slope movement – fence post or trees may move over time. • Slump – Blocks of land fall straight down. • Earth flow – Mass of weathered material and water move down slope. • Mudflow – rapid movement of water with large amounts of suspended clay and silt

17. Chapter 12.4

18. Soil as a resource • Less than 25% of earth’s land can be used for crop growing.

19. Soil fertility – the ability of soil to grow plants • Determined by the minerals, water and organic matter in the soil • Soil Depletion • Caused by crop plants using up the soils nutrients and not being replaced because the organic material from the plants is not replaced • Fertilizers are used to replenish nutrients, but cause serious environmental damages. • Salinization – When desert soils are artificially watered, the water leaves behind minerals that accumulate over years and the soils can no longer sustain crops.

20. Erosion and Soil Conservation • Types of Soil Conservation • Windbreaks – trees planted along fields to break up the wind • Constructing terraces – to slow the water running downhill • Contour forming – Plow with the contour lines to reduce the speed of downhill water. • Strip farming – Alternate bare ground crops (corn) with ground covering crops (alfalfa).