What is Weathering? Weathering is the chemical or physical breakdown of a rock or mineral due to exposure to the atmosphere.

Physical or (mechanical Weathering Physical or (mechanical) : mechanical breakdown of rock or minerals. Just breaks into smaller pieces, composition of the material is NOT changed!!

Chemical : decomposition of material. Chemical Weathering Chemical : decomposition of material. The composition IS Changed!!! You get something new! Oxidation of Sandstone: turns RED!

Physical (Mechanical) Weathering There are several different types of physical weathering: 1.) Frost or Ice Wedging –The breaking down of rock by the force exerted by water expanding as it freezes into ice.

Frost Wedging animation Frost Wedging Cont…. Water expands as it freezes, this breaks the rock into angular fragments. Occurs A LOT in Western New York –Causes most POTHOLES!!!! Will ONLY occur in areas where the temperature alternates above freezing and below freezing!!! Frost Wedging animation

2.) Exfoliation Exfoliation – Erosion of upper rock causes underlying rock to expand resulting in cracking and peeling of rock in slabs. Think of onion skin layers and peeling them off!!

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

3.) Organic Activity

3.) Organic Activity (plant and animal) Organic Activity – plant roots or animals like burrowing worms can cause rock to breakdown.

PHYSICAL WEATHERING – ROOT ACTION PLANT ROOTS UPLIFT AND FRACTURE ROCK

4.) Wetting/Drying Wetting and Drying - addition of water to mineral structure causes structure to expand. Mudcracks form from the wetting and drying of clay material.

Important!!! What happens to the erosion rate when you increase the surface area? Physical weathering increases the surface area of rocks/minerals. Taking a rock/mineral and breaking it up into smaller pieces causes it to take up more space (surface area) and will eventually increase the rate of chemical weathering to occur.

Physical Weathering occurs Let’s Work This Through! Starting Volume:_______________ Volume:________________________ Total Surface Area:____________ Surface Area:__________________ (2 feet)3 = 8ft3 (2 feet)3 = 8ft3 6 x (2ft)2=24ft2 6 x (1foot)2 x 8 = 48ft2

Chemical Weathering Hydrolysis – the chemical reaction between water and other substances. Silicate minerals will often form clay from this process. Kaolin mine, central Georgia (feldspar weathered into clay by hydrolosis)

Hydrolysis cont… Halite, gypsum, and limestone are most susceptible to becoming weathered by water, and most compounds are at least slightly soluble in water, so water is called the UNIVERSAL SOLVENT. Chemically Weathered Limestone

2.) Carbonation Carbonation (Carbonic Acid) – dissolving of substances by acids in water often leaving insoluble remains. Carbonic Acid can devastate rocks made of calcite. Rocks such as limestone and dolomite can be entirely dissolved, leaving extensive caverns.

Caves formed from Carbonation

3.) Oxidation Oxidation – chemical reaction of a substance with oxygen causing a rust material to form. Note: Most rocks/minerals will appear RED in color after an oxidation reaction. Oxidation of Sandstone

Weathering and Climate So, what effect does climate have on weathering? Climate plays a very important role in weathering. The temperature and amount of moisture influences the type of weathering that will occur. Warm and wet climates produce mostly chemical weathering. Never any frost wedging. Cool and slightly wet climates produce mostly physical weathering.

Factors Effecting Weathering Rate Low Highly resistant minerals Massive rocks (big blocks) Little to no rainfall Low temperatures Little or no soil Little organic activity Medium Moderately resistant minerals Average rock size Some rainfall Medium temperatures Soil is present Organic activity is moderate High Unstable minerals (easily broken down) Small rock particles Heavy rainfall High temperatures Thick soils A lot of organic activity

80 years later: look what’s happened Cleopatra’s Needle 80 years later: look what’s happened Cleopatra’s Needle in Egypt: warm, dry climate, little to not weathering occurs. Cleopatra’s Needle was moved to New York and has weathered significantly on only 80 years due to: cold and wet climate

Weathering and Resistance The harder the rock or mineral is, the more resistant it will be to weathering. Any rock with quartz will be quite resistant due to quartz’s hardness. Rocks made mostly of calcite, a very soft mineral, will be easily weathered.

WHAT KIND OF CLIMATE SUPPORTS WEATHERING? HIGH PPT ↑ LOW COLD →→→→→→→→→→ HOT

CLIMATE CONTROLS WEATHERING How will the landscape be different for arid regions compared to moist regions? Sketch the diagram. PHYSICAL WEATHERING: COLD AND MOIST ALTERNATE FREEZE / THAW CHEMICAL WEATHERING: WARM AND MOIST IN BOTH CASES – WATER IS THE PRIMARY INGREDIENT THAT PROMOTES WEATHERING

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 which is organic material.

Soil Development Size and thickness of each horizon depends on: Climate Vegetation Slope (gradient or incline) Time

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 – THE PRODUCT OF WEATHERING AFTER THOUSANDS OF YEARS…

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

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