2THINK!!!!Imagine the tiniest rock you have ever found. How did it get so small? It didn’t start out that way! What forces created this rock?
3Weathering is the breaking down of rocks and other materials on the earth’s surface
4What is the difference between weathering and erosion?
5Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animalsErosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity
7Mechanical/Physical Weathering 2 Types of WeatheringMechanical/Physical Weatheringprocesses that break a rock or mineral into smaller pieces without altering its compositionChemical Weathering processes that change the chemical composition of rocks and minerals
8What is Mechanical/Physical Weathering? A rock is physically changed without achange in chemical compositionProcesses include:Frost Action / Ice WedgingAbrasion by wind and waterPlant and Animal ActionThermal Expansion and contractionPressure Unloading / Exfoliation
9Frost Action / Ice Wedging Alternating freezing and thawing of water causes material to break upExample – Pot holes, Ice cubes in an ice trayWater expands between 4 and 0 degrees CelsiusVolume increases by 9%!!!!The Bigger the crack gets, the more water it lets in……causing a snowball effect
18Thermal Expansion and Contraction Extreme changes in temperature may cause cracking
19Pressure Unloading / Exfoliation Cracking at weak joints due to a release of pressureCause and effect of ExfoliationRock breaks off into leaves or sheets along joints which parallel the ground surfaceExpansion of rock due to uplift and erosionremoval of pressure of deep burialOccurs often in bedrock when glaciers recede
28Acid Reactions / Carbonation Carbon reacts with other substances to alter the chemical makeup of rocksExample: Carbonic acids (water + carbon dioxide) dissolve limestone which can results in the formation of underground cavesNitric acids produced by the decay of organic material can alter soil composition
29Caves are formed when Carbonic Acid dissolves limestone
30Stalactites (from the top) and Stalagmites (from the bottom) are formed in a limestone cave as a result of Chemical Weathering
32Nitric Acids in SoilWhen organisms or plants decay Nitric Acid is produced. This is absorbed into the soil and the chemical make-up of the soil has been changed.
33Differential Weathering The variable rate of which rocks weather is called differential weatheringFactors affecting the rate of weathering include:Composition (granite vs. limestone)Climate (hot, wet, cold, dry)Rock size (surface area)
34Rocks weather at different rates due to. differences in mineral Rocks weather at different rates due to differences in mineral composition. The harderthe rock, the slower therate of weathering is.Some minerals are more Stable at the earth’s surface thanothers! These takelonger to weather.Composition dictateshardness which determinesresistance to weathering.
35The climate that a rock is in is a factor in the rate of weathering. Cold Climates– mechanical weathering breaks down rocks rapidlyWarm, wet climates –chemical weathering breaks down rocks rapidly
36How much exposed area of the rock will also effect weathering In which shape will weathering occur faster?
37EROSION/DEPOSITIONThe process of removing Earth materials from their original sites through weathering and transport agents or forcesTransport Agents or Forces include:Water (Rain, streams, rivers, oceans, and ice/glaciers)WindGravity
48What is the difference between Weathering and Erosion? REVIEWWhat is the difference betweenWeathering and Erosion?Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down by air, water, plants and animalsErosion - process of removing Earth materials from their original sites through weathering and transport by water, wind or gravity
49REVIEW- 2 Types of Weathering Mechanical/Physical Weathering - A rock is physically changed without a change in chemical compositionFrost Action / Ice Wedging Alternating freezing and thawing of water causes material to break upAbrasion by wind and water Wearing down or smoothing of a material due to constant collisionsPlant and Animal Action Plant root growth and animals burrowing increase the exposure of rocks to the air and water and causes breakdownThermal Expansion and contraction Extreme changes in temperature causes crackingPressure Unloading / Exfoliation Earth’s forces can push rock that formed deep underground up to the surface. The pressure causes the rock to expand and crack. This leads to exfoliation.Mechanical/Physical Weathering - In the natural process of mechanical weathering, physical forces split rocks apart but do not change their composition (like smashing a walnut).
50REVIEW -2 Types of Weathering Chemical Weathering - Processes that change the chemical composition of rocks and mineralsHydrolysis Water is very slow reaction and the main cause of chemical weathering.Oxidation Where Oxygen combines with other substances to produce rustAcid Reactions / Carbonation Carbon reacts with other substances to dissolve and alter the chemical makeup of rocks forming caves. Nitric acid produced by the decay of organic material can alter soil composition
51REVIEW (Continued)Differential Weathering - The variable rate of which rocks weather is called differential weathering. Most weathering occurs over long periods of time- hundreds, thousands, or even millions of years.Factors affecting the rate of weathering include:Composition (granite vs. limestone) What minerals a rock is made fromClimate (hot, wet, cold, dry) hot, wet regions weather rocks faster than cold, dry onesRock size (surface area) How large or small a rock’s surface is