WEATHERING Definition: The physical and chemical processes that break down rock on earth’s surface.
2 Types of Weathering PHYSICAL/ MECHANICAL WEATHERING – rocks are fractured and broken apart increasing the surface area. Initial product = Final product CHEMICAL WEATHERING – Chemical reactions dissolve minerals that were stable when the rocks were formed below the surface to types that are now stable at surface temperatures and pressure. Products have different chemical composition than the original. Initial product ≠ Final product
EXAMPLES OF CHEMICAL WEATHERING OXIDATION OCCURS when free oxygen combines chemically with metallic elements (usually iron) AKA RUST
CARBONATION Water containing carbonic acid dissolves minerals (all rain water is slightly acidic) Most strongly affected are calcite minerals: limestone and marble
CARBONATION Stalagmites and stalactites
CARBONATION – SINK HOLES Karst Topography forms caves, caverns, and sinkholes
CAVES AND SINK HOLES
CHEMICAL WEATHERING HYDRATION OCCURS WHEN Water combines with minerals – most often in granite (mica and feldspars) to form CLAY
PHYSICAL WEATHERING FROST ACTION – FROST WEDGING MOST IMPORTANT IN OUR CLIMATE FROST ACTION – FROST WEDGING ALTERNATE FREEZE AND THAW
ROCKS ARE CRACKED BY WATER FREEZING
EXAMPLES: POT HOLES AND FROST HEAVES
PHYSICAL WEATHERING – ROOT ACTION PLANT ROOTS UPLIFT AND FRACTURE ROCK
PHYSICAL WEATHERING - ABRASION SCRAPE, GRIND AND WEAR AWAY ROCK DURING EROSION WATER WIND
PHYSICAL WEATHERING EXFOLIATION – PEELING AWAY OF ROCK due to unloading (reduced pressure at earth’s surface) or fluctuations in temperature. Rocks expand and crack
PHYSICAL WEATHERING - EXFOLIATION
PHYSICAL WEATHERING INCREASES SURFACE AREA MORE CHEMICAL WEATHERING CAN OCCUR
WHAT KIND OF CLIMATE SUPPORTS WEATHERING? HIGH PPT ↑ LOW COLD →→→→→→→→→→ HOT
CLIMATE CONTROLS WEATHERING PHYSICAL WEATHERING: COLD AND MOIST ALTERNATE FREEZE / THAW CHEMICAL WEATHERING: WARM AND MOIST IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERING
Question 41 from the most recent Regents exam – August ‘07
Differential Weathering Masses of rock do not weather uniformly due to regional and local factors Results in many unusual and spectacular rock formations and landforms
Question #9 from January ’07 exam
WHICH DIAGRAM IS AN ARID CLIMATE? HUMID CLIMATE? B
Question #27 from the August ’04 exam
WHICH LAYER IS MORE RESISTANT TO WEATHERING? LEAST RESISTANT? D C B
YOU MIGHT ALSO SEE IT LIKE THIS.
THE END PRODUCTS OF WEATHERING CALLED SEDIMENTS OR SOIL SOIL: a combination of sediment, rock minerals, and humus (organic material)
SOIL – THE PRODUCT OF WEATHERING AFTER THOUSANDS OF YEARS…
SOIL HORIZONS Layers that develop as a result of the weathering processes, biologic activity, and leaching (flow of water through rocks) O = Organic. It consists of fragments of leaf litter, twigs, roots, and other organic material lying on the surface of the soil. This layer is not present in cultivated fields. A = Topsoil. It is usually darker than lower layers, loose, and crumbly with varying amounts of organic matter. This is generally the most productive layer of soil. B = Subsoil. It is usually light colored, dense, and low in organic matter. C = Parent Material. Partially decomposed parent material The unconsolidated organic and mineral material in which soil forms.. R = Bedrock. The solid rock that underlies the soil and other unconsolidated material
Soil Development Size and thickness of each horizon depends on: Climate Vegetation Slope (gradient or incline) Time
2 TYPES OF SOIL TRANSPORTED SOIL: SOIL CARRIED BY EROSION AND DEPOSITED ON THE BEDROCK (MOST SOIL IS TRANSPORTED) RESIDUAL SOIL: SOIL FORMED BY THE WEATHERING OF THE BEDROCK DIRECTLY BENEATH IT
Question #25 from the August ’06 exam
TRANSPORTED SOILS DUE TO …
FERTILE SOIL IS EXTREMELY VALUABLE FOR FOOD PRODUCTION
WEATHERING SUMMARY WEATHERING IS THE BREAKDOWN OF ROCK INTO SEDIMENTS PHYSICAL WEATHERING – INCREASES SURFACE AREA - COLD/HUMID CLIMATE CHEMICAL WEATHERING – WARM/HUMID CLIMATE IN BOTH CASES, WATER IS THE PRIMARY INGREDIENT