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