Weathering The Breakdown of Rocks. What is Weathering? The physical breakdown (disintegration) and...
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Transcript of Weathering The Breakdown of Rocks. What is Weathering? The physical breakdown (disintegration) and...
Weathering
The Breakdown of Rocks
What is Weathering?• The physical breakdown (disintegration) and chemical
alteration (decomposition) of rocks
• 2 types– Mechanical weathering– Chemical Weathering
Yellowstone, 2004
Weathering
• Mechanical Weathering
– Physical disintegration of rock
– Results in smaller fragments
• Chemical Weathering
− Internal structure of a mineral is altered
− A new mineral is formed
Weathering Examples
• Mechanical weathering • Chemical weathering
Mechanical Weathering• Rocks are broken into smaller pieces without
changing the rock’s mineral composition
• 3 types– Frost wedging– Unloading– Biological activity
Mechanical – Frost Wedging
• Breaking of rock from freezing and thawing
Mammoth, Twin Lakes (2006)
• Repeated expansion and contraction break rock bodies into angular pieces (talus)
Mechanical - Unloading• Erosion removes overlying rock• Decreases pressure• Underlying rocks rise and expand
• Rocks break off in layers (exfoliation)
Mechanical – Biological Activity
• Organisms break rock into fragments
− Plants
− Humans
− Animals
Chemical Weathering• Chemical transformation of rock into one or more
new compounds
• 3 Types– Oxidation – Hydration – Carbonation
Feldspar Kaolinite
Chemical - Oxidation• Oxygen reacts with minerals and forms iron
oxide (rust)
− Results in rocks with a reddish or yellowish coloring
Bryce National Park
Chemical - Hydration• Water interacts with minerals and forms clays
− Granite composed of silicate minerals (feldspar, hornblende and biotite)
− Silicate minerals weather into clays (kaolinite)
Chemical - Carbonation• Carbon dioxide combines with water and forms
a weak acid (carbonic acid)• Dissolves limestone
Shells (CaCO3)Limestone CavesCaves Stalactites
Rates of Weathering
• Factors controlling weathering rates
− Rock Characteristics
− Climate
− Differential Weathering
Rock Characteristics• Composition
– Certain rocks are more resistant to weathering• Particle size
– Small pieces generally weather faster than larger pieces• Joints & Fractures
– Allows water to penetrate between cracks
MarbleGranite
Climate
• Warm, moist areas tend to weather minerals faster
Differential Weathering• Certain rock types are more resistant to
weathering
− Volcanic neck and dikes are more resistant
Which will Weather Faster?
Boulder vs. Pebbles
Which Area Will a Faster Rate of Weathering?
Mammoth vs. Maui
What Type of Weathering is Displayed?
Oxidation & Differential Weathering