Unit One A Changing Earth

1. Unit OneA Changing Earth Chapter Two Weathering and Erosion

2. WeatheringandErosionWeathering • Rock Cycle • Rocks are classified into three categories • Sedimentary, Igneous (formed when magma cools), Metamorphic • RockCycle – the process of change that scientists think happens to rock • Weathering – processes that break rocks into smaller pieces or decompose them through chemical activity • Takes place at or near the surface of the earth • Forms soil, replenishes minerals for plant growth

3. WeatheringandErosionWeathering • Rock Cycle (continued) • Two kinds of weathering • Mechanical weathering – process of breakingdown rocks into smaller pieces • Chemical weathering – changing rocks into different substances

4. WeatheringandErosionWeathering • Mechanical (Physical) Weathering • The process of breaking down rocks into smaller pieces • Factors that contribute to mechanical weathering • Temperature, water, wind, plant and animal life • Examples of mechanical weathering • Frost wedging (frost action) – frozen water in a rock causes the rock to crack • Frost heaving – frozen water under a rock expands and lifts the rock

5. WeatheringandErosionWeathering • Mechanical (Physical) Weathering • Examples of mechanical weathering (continued) • Pressure release – great pressure on a rock is suddenly released, causing cracks and breaks in the rock • Exfoliation – sheets of rock peel away like layers of an onion • Abrasion – occurs when rocks rub against each other • Caused by water and wind • Hoodoos – form when soft rock abrades more quickly than harder rock above it

6. WeatheringandErosionWeathering • Chemical Weathering • Changes the rock into a different substance • Types of chemical weathering • Oxidation – a process that occurs whenever a substance combines with oxygen to form a new substance. When oxygen combines with iron, iron oxide (or rust) is formed • Reaction of acids with minerals • Carbonic acid – a weak acid formed when water and carbon dioxide mix

7. WeatheringandErosionWeathering • Chemical Weathering • Types of chemical weathering (continued) • Acid rain – rain that contains sulfuric acid, carbonic acid and other chemicals; cities are often exposed to acid rain because of industrial smoke and exhaust from cars; caused by burning fossil fuels such as coal and oil • Lichens – secrete mild acids that dissolve the rocks and further break down the rocks into the soil

8. WeatheringandErosionWeathering • Caves • Crashing waves, wind and running water form caves by mechanical weathering • Chemical weathering forms limestone caves as acidic water seeps into cracks in limestone, dissolving calcite in the limestone, which causes cavities to form • Speleothems – beautiful formations in caves, formed as the dissolved calcite is deposited out of the water (chemical weathering) • Drip curtain – a speleothem that forms when seeping water hardens along a crack, forming a thin curtain-like sheet

9. WeatheringandErosionWeathering • Caves • Stalactites – structures in caves that hang from the ceiling and look like stone icicles • Stalagmites – structures in caves that “grow” up from the ground as a result of the dripping of dissolved calcite • Column – formed when a stalactite and a stalagmite grow together • Spelunkers – people who enjoy exploring caves

10. WeatheringandErosionWeathering • Soil • Soil – the loose material at the surface of the earth made up of weathered particles, decayed organic material (humus), air, and water

11. WeatheringandErosionWeathering • Soil – Soil particles • Pedologists – scientists who study soil • Three basic sizes of soil particles • Sand – largest kind of particle in soil; drains quickly • Clay – smallest kind of particle in soil; holds nutrients and water well; 100,000 particles of clay = 1 particle of sand • Silt – particle that allows water and air to mix in the soil

12. WeatheringandErosionWeathering • Soil – Soil texture and formation • Texture – refers to how much of each kind of particle is in the soil sample • Loam – a fertile soil where sand, clay, and silt are all equally evident • Texture is important to farming because certain crops grow best in certain textures • Kinds of weathered rock, climate and vegetation determine the composition and fertility of soil

13. WeatheringandErosionWeathering • Soil – Soil horizons • Horizons – multiple layers of soil • O Horizon – top layer of soil made of leaf litter and humus • Topsoil – A Horizon; made of minerals from weathered rock and humus; plants germinate and roots grow in this layer • Subsoil – B Horizon; contains weathered minerals and some nutrients from the humus

14. WeatheringandErosionWeathering • Soil – Soil horizons (continued) • C Horizon – consists mainly of larger weathered fragments of the bedrock; contains clay and sand particles, but very little organic material (humus); rich in minerals • Bedrock – R Horizon; regolith; unweathered rock that influences the texture of the soil above it

15. WeatheringandErosionWeathering • Diagram Topsoil Subsoil Bedrock 1 2 3

16. WeatheringandErosionErosion • Agents of Erosion • Sediment – small particles produced by weathering • Erosion – moves the weathered material from one place to another • Weathering and erosion often occur together • Weathering is the breaking down of rocks and erosion moves the broken-down material from one place to another

17. WeatheringandErosionErosion • Agents of Erosion (continued) • The primary force behind erosion is gravity • Agentsoferosion – other factors involved in the transportation of weathered material such as water, wind, and ice • Deposition – the dropping of sediment (small particles) and rocks in a new location • Depositions often have a layered look because sediment settles according to its weight. The heaviest sediment drops first and the lightest drops last, causing layers

18. WeatheringandErosionErosion • Mass Movements • Massmovement – erosion that is primarily caused by gravity • Five kinds of mass movement • Soil creep – gravity pulling soil slowly down the slope of a hill • Earth flow – gravity pulling rock and sediment down a hill • Mudflow – when water and soil combine and gravity pulls them down a hill • Rockslides – huge slabs of rock sliding down a mountain • Avalanche – when gravity pulls huge amounts of snow down a mountain

19. WeatheringandErosionErosion • Stream Erosion • Load – sediment carried by a stream • Dissolved load – sediment that dissolves in the stream and is transported to larger bodies of water • The faster a stream moves, the more sediment it can pick up and move • Suspended load – sediment that is carried by a stream but is not dissolved

20. WeatheringandErosionErosion • Stream Erosion (continued) • Floodplain – an area where a river or stream commonly floods • Yearly flooding provides nutrients to some farmland • Delta – area at the mouth of the river where there are deposits of sediment that are rich in nutrients • Birdfoot delta – the Mississippi Delta because the erosion has not formed a triangular shape. The many channels running in different directions resemble a bird’s foot

21. WeatheringandErosionErosion • Wave Erosion • Waves erode away the beach and deposit the sand in new places • The shoreline constantly changes as wave erosion and deposition takes place • Sand bars constantly shift positions and form new areas of land and shallow places along the coast • The bigger and more powerful waves from storms, such as hurricanes, increase wave erosion and deposition

22. WeatheringandErosionErosion • Wind Erosion • Wind is the agent of erosion in dry areas, such as deserts • Deflation – wind picking up loose sediment and carrying it away • Two kinds of wind erosion • Dust storms – when wind blows small, loose particles such as clay and silt • Sandstorms – sand particles are heavier, so these storms are closer to the ground • The prevailing wind determines the size and shape of sand dunes

23. WeatheringandErosionErosion • Ice Erosion • Glaciers – formed when layers of unmeltedsnow compact and turn to ice • Plucking – large pieces of bedrock are pulled out of the ground and carried along the mountainside • Moraines – piles of rocks and soil caused by a glacier

24. WeatheringandErosionCauses of Erosion • Causes of Erosion • Water, wind and ice are agents of erosion • Water may cause some materials to weather • However, most weathering is done by the sediment and loads carried by water, wind, and ice • The agents of erosion are mainly the means to transport weathered materials