Weathering & Erosion. Does the Earth’s surface change over time?
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Transcript of Weathering & Erosion. Does the Earth’s surface change over time?
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Weathering & ErosionWeathering & Erosion
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Does the Earth’s surface change over time?
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What shapes the Earth’s surface over time?
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Weathering and Erosion
Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down
Erosion - process of removing Earth materials from their original sites through weathering and transport
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What evidence of weathering do you see in this picture?
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Types of WeatheringMechanical (Physical) - processes that break a rock or mineral into smaller pieces without altering its composition
Chemical - processes that change the chemical composition of rocks and minerals
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Mechanical Weathering
1. Abrasion/Scouring – wind & water
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What evidence of weathering do you see in this picture?
Why wasn’t this mass of land weathered
away?
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Mechanical Weathering2. Frost wedging – water expands when it freezes
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Frost Wedging
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Mechanical Weathering3. Exfoliation/Unloading
– As deeply buried rock is uplifted, pressure is reduced and the rock breaks off into leaves or sheets along joints
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Enchanted Rock
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Mechanical Weathering
4. Thermal Expansion/Contraction – repeated, daily heating (expansion) and cooling (contraction) of rock causes stress along natural boundaries in the rock
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Mechanical Weathering5. Plant/Animal Activity – plant roots, animal burrows
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Mechanical Weathering
6. Crystal Growth – water evaporates leaving minerals (salt) behind; crystals grow and fracture the rock
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Chemical WeatheringChemical Weathering
• Rock reacts with water, gases and solutions which add or remove elements from minerals
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Chemical WeatheringChemical Weathering1. Oxygen1. Oxygen
– Iron combines with oxygen in the presence of water in a processes called oxidation. The product is rust.
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Chemical WeatheringChemical Weathering
2. Carbon Dioxide2. Carbon Dioxide– CO2 dissolves in rain water and creates
carbonic acid which easily weathers limestone and marble
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1908 to 1969
Acid rain has eaten away this limestone statue
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Chemical WeatheringChemical Weathering3. Biological Activity3. Biological Activity
– Lichen that grow on rocks produce weak acids that chemically weather rock
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Erosion is caused by…Erosion is caused by…1. Water1. Water – Rain, Streams, Oceans, Ice
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Erosion is Caused by…Erosion is Caused by…
2. Wind2. Wind
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Erosion is Caused by…Erosion is Caused by…
3. Gravity3. Gravity
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Mass WastingMass Wasting
• Movement of large amounts of material downhill under the influence of gravity – Creep Creep – SolifluctionSolifluction– MudflowMudflow– Earthflow Earthflow – Slump Slump – Rockfall Rockfall – AvalancheAvalanche
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Soil Creep
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Creep
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Slump
scarp
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Slump near Fargo, ND
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Earthflow
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Rockfalls, Yosemite, California
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Triggers for rapid Mass Wasting
• Rain
• Over-steepening– cutting at foot of slope– piling on head of slope
• Deforestation / Devegetation
• Earthquakes
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