Weathering & 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 Weathering Mechanical (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 Weathering 2. Frost wedging – water expands when it freezes

Frost Wedging

Mechanical Weathering 3. 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 Weathering 5. 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 Weathering Rock reacts with water, gases and solutions which add or remove elements from minerals

Chemical Weathering 1. Oxygen Iron combines with oxygen in the presence of water in a processes called oxidation. The product is rust.

Chemical Weathering 2. Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid which easily weathers limestone and marble

Acid rain has eaten away this limestone statue

Chemical Weathering 3. Biological Activity Lichen that grow on rocks produce weak acids that chemically weather rock

Erosion is caused by… 1. Water – Rain, Streams, Oceans, Ice

Erosion is Caused by… 2. Wind

Erosion is Caused by… 3. Gravity

Mass Wasting Movement of large amounts of material downhill under the influence of gravity Creep Solifluction Mudflow Earthflow Slump Rockfall Avalanche

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