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Unit One A Changing Earth. Chapter Two Weathering and Erosion. Weathering and Erosion Weathering. Rock Cycle Rocks are classified into three categories Sedimentary, Igneous (formed when magma cools), Metamorphic Rock Cycle – the process of change that scientists think happens to rock

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unit one a changing earth

Unit OneA Changing Earth

Chapter Two

Weathering and Erosion

weathering and erosion weathering
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
weathering and erosion weathering1
WeatheringandErosionWeathering
  • Rock Cycle (continued)
    • Two kinds of weathering
      • Mechanical weathering – process of breakingdown rocks into smaller pieces
      • Chemical weathering – changing rocks into different substances
weathering and erosion weathering2
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
weathering and erosion weathering3
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
weathering and erosion weathering4
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
weathering and erosion weathering5
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
weathering and erosion weathering6
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
weathering and erosion weathering7
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
weathering and erosion weathering8
WeatheringandErosionWeathering
  • Soil
    • Soil – the loose material at the surface of the earth made up of weathered particles, decayed organic material (humus), air, and water
weathering and erosion weathering9
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
weathering and erosion weathering10
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
weathering and erosion weathering11
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
weathering and erosion weathering12
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
weathering and erosion weathering13
WeatheringandErosionWeathering
  • Diagram

Topsoil

Subsoil

Bedrock

1

2

3

weathering and erosion erosion
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
weathering and erosion erosion1
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
weathering and erosion erosion2
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
weathering and erosion erosion3
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
weathering and erosion erosion4
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
weathering and erosion erosion5
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
weathering and erosion erosion6
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
weathering and erosion erosion7
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
weathering and erosion causes of erosion
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