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Weathering & ErosionWeathering & Erosion
Does the Earth’s surface change over time?
What shapes the Earth’s surface over time?
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
What evidence of weathering do you see in this picture?
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
Mechanical Weathering
1. Abrasion/Scouring – wind & water
What evidence of weathering do you see in this picture?
Why wasn’t this mass of land weathered
away?
Mechanical Weathering2. Frost wedging – water expands when it freezes
Frost Wedging
Mechanical Weathering3. Exfoliation/Unloading
– As deeply buried rock is uplifted, pressure is reduced and the rock breaks off into leaves or sheets along joints
Enchanted Rock
Mechanical Weathering
4. Thermal Expansion/Contraction – repeated, daily heating (expansion) and cooling (contraction) of rock causes stress along natural boundaries in the rock
Mechanical Weathering5. Plant/Animal Activity – plant roots, animal burrows
Mechanical Weathering
6. Crystal Growth – water evaporates leaving minerals (salt) behind; crystals grow and fracture the rock
Chemical WeatheringChemical Weathering
• Rock reacts with water, gases and solutions which add or remove elements from minerals
Chemical WeatheringChemical Weathering1. Oxygen1. Oxygen
– Iron combines with oxygen in the presence of water in a processes called oxidation. The product is rust.
Chemical WeatheringChemical Weathering
2. Carbon Dioxide2. Carbon Dioxide– CO2 dissolves in rain water and creates
carbonic acid which easily weathers limestone and marble
1908 to 1969
Acid rain has eaten away this limestone statue
Chemical WeatheringChemical Weathering3. Biological Activity3. Biological Activity
– Lichen that grow on rocks produce weak acids that chemically weather rock
Erosion is caused by…Erosion is caused by…1. Water1. Water – Rain, Streams, Oceans, Ice
Erosion is Caused by…Erosion is Caused by…
2. Wind2. Wind
Erosion is Caused by…Erosion is Caused by…
3. Gravity3. Gravity
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
Soil Creep
Creep
Slump
scarp
Slump near Fargo, ND
Mass Wasting in Haiti
Earthflow
Rockfalls, Yosemite, California
Triggers for rapid Mass Wasting
• Rain
• Over-steepening– cutting at foot of slope– piling on head of slope
• Deforestation / Devegetation
• Earthquakes