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Chapter Two Weathering and Erosion Unit One A Changing Earth.

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Presentation on theme: "Chapter Two Weathering and Erosion Unit One A Changing Earth."— Presentation transcript:

1 Chapter Two Weathering and Erosion Unit One A Changing Earth

2 Weathering and Erosion Weathering  Rock Cycle  Rocks are classified into three categories  Sedimentary, Igneous (formed when magma cools), Metamorphic  Rock Cycle – the changing and transforming of rock as it undergoes weathering, heat, and pressure  Weathering – process that breaks rocks into smaller pieces or decomposes them through chemical activity  Takes place at or near the surface of the earth  Forms soil, replenishes minerals for plant growth

3 Weathering and Erosion Weathering  Rock Cycle (continued)  Two kinds of weathering  Mechanical weathering – process of breaking down rocks into smaller pieces  Chemical weathering – changing rocks into different substances

4 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  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 the harder rock above it

6 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  Soil  Soil – the loose material at the surface of the earth made up of weathered particles, decayed organic material (humus), air, and water

11 Weathering and Erosion Weathering  Soil – Soil particles  Pedologist – scientist who studies 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 Weathering and Erosion Weathering  Soil – Soil texture and formation  Texture – refers to how much of each kind of particle is in the soil sample  Loam – a soil that contains equal parts of sand and silt with about half as much clay  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 Weathering and Erosion Weathering  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 Weathering and Erosion Weathering  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 parent rock that influences the texture of the soil above it

15 Weathering and Erosion Weathering  Diagram 1.Topsoil 2.Subsoil 3.Bedrock 2 1 3

16 Weathering and Erosion Erosion  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 Weathering and Erosion Erosion  Agents of Erosion (continued)  The primary force behind erosion is gravity  Agents of erosion – 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 Weathering and Erosion Erosion  Mass Movements  Mass movement – erosion that is primarily caused by gravity  Five kinds of mass movement  Soil creep – gravity pulling soil slowly down the slope of a hill; results in leaning trees and fences  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 Weathering and Erosion Erosion  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 Weathering and Erosion Erosion  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 - the current and waves in the Gulf of Mexico have caused it to be shaped differently.

21 Weathering and Erosion Erosion  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 Weathering and Erosion Erosion  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 – when wind blows sand

23 Weathering and Erosion Erosion  Ice Erosion  Glaciers – formed when layers of snow that haven’t melted compact and turn to ice  Plucking – large pieces of bedrock are pulled out of the ground by a glacier and carried along the mountainside  Moraines – piles of rocks and soil left behind by a glacier

24 Weathering and Erosion Causes 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


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