2 Objectives Describe the two major kinds of rock weathering. Identify three end products of weathering.Explain the difference between weathering, erosion, and mass wasting.Describe how ice, water, and air transport regolith across Earth’s surface.Define and give examples of mass wasting by slope failure and/or sediment flow.
4 Weathering-The First Step in the Rock Cycle How rocks disintegrateWeatheringThe chemical and physical breakdown of rock exposed to air, moisture and living organismsRegolithA loose layer of fragments that covers much of Earth’s surfaceSoilThe uppermost layer of regolith, which can support rooted plantsThe rock in the photo has weathered in place with little erosion, forming soil
5 Weathering: Two Types Mechanical engineering Chemical weathering The breakdown of rock into solid fragments by physical processesChemical composition of rock NOT alteredChemical weatheringThe decomposition of rocks and minerals by chemical and biochemical reactions
6 JointsA fracture of rock , along which no appreciable movement has occurredSheet jointing or exfoliationFrost wedgingAbrasionThe gradual wearing down of bedrock by the constant battering of loose particles transported by wind, water or iceThe jointing in these rocks has exposed new surface area which has broken and smoothed due to wind, water and ice.
9 Chemical weathering Dissolution The separation of materials into ions in a solution by a solvent, such as water or acidRainwater acts as weak solution of carbonic acidAnthropogenic actions influence acidity of rainwaterThe marble grave marker has been attacked by acidic rain because of the calcite composition. The grave marker on the right, while old, has not been dissolved because of its granite composition
10 Chemical weathering: ion exchange and the chemical breakdown of feldspar
11 Factors affecting weathering Tectonic settingYoung, rising mountains weather relatively rapidlyMechanical weathering most common
12 Factors affecting weathering Rock compositionMinerals weather at different ratesCalcite weathers quickly through dissolutionQuartz is very resistant to chemical and mechanical weatheringMafic rocks with ferromagnesian minerals weather more easily
13 Factors affecting weathering Rock structureDistribution of joints influence rate of weatheringRelatively close joints weather faster
14 Factors affecting weathering TopographyWeathering occurs faster on steeper slopesRockslides
15 Factors affecting weathering VegetationContribute to mechanical and chemical weatheringPromotes weathering due to increased water retentionVegetation removal increases soil lossVegetation can both hold waterAnd increase weathering. If removedRocks may also be vulnerable to abrasion
16 Factors affecting weathering Biologic activityPresence of bacteria can increase breakdown of rock
17 Factors affecting weathering ClimateChemical weathering is more prevalent in warm, wet tropical climatesMechanical weathering less important hereMechanical weathering is more prevalent in cold, relatively dry regionsChemical weathering occurs slowly hereNote: temperate regions such as at the center of the chart undergo both chemical and mechanical weathering, i.e. New York area
18 Factors affecting weathering: color dots on map match colors on chart
19 Products of Weathering ClayTiny mineral particles of any kind that have physical properties like those of the clay mineralsClays are hydrous alumino-silicate minerals
20 Products of Weathering SandA sediment made of relatively coarse mineral grainsSoilMixture of minerals with different grain sizes, along with some materials of biologic originHumusPartially decayed organic matter in soil
21 Erosion and Mass Wasting Erosion is the removal of weathering products from the source and most often occurs by waterErosionThe wearing away of bedrock and transport of loosened particles by a fluid, such as waterExample: Sediment moved along the bottom of a stream
22 Erosion and Mass Wasting Erosion by windParticles of sand are transported close to the surface.finer particles of silt and clay can be transported great distancesErosion by iceGlacierA semi-permanent or perenially frozen body of ice, consisting of recrystallized snow, that moves under the pull of gravityWind-blown fine sediments such as this dust cloud canBe transported across oceans
23 Erosion and Mass Wasting Left: deposits of unsorted glacial till from glacier Right: rock polished and striated by glacier
24 Erosion by ice: glacier removes, breaks and transports rock pieces glaciers scour valleys and deposit piles of debris as moraines
25 Erosion and Mass Wasting The downslope movement of regolith and/or bedrock masses due to the pull of gravitySlope failureFalling, slumping or sliding of relatively coherent masses of rock
26 Erosion and Mass Wasting: Rock slide, rock fall, and slumping result in downhill transport of broken rock
27 Erosion and Mass Wasting Flow: If water or air combines with the downward movement, the regolith can “flow” downhillCreepThe imperceptibly slow downslope flow of regolithUnstable slopes move very slowly over long periods of time
29 Why do major landslides occur near plate boundaries? Tectonics and mass wastingWorld’s major historic landslides clustered near converging lithospheric platesHigh mountains undergo rapid weatheringEarthquakes near plateboundaries can trigger landslidesThis massive slide was triggered byA magnitude 9 earthquake in Alaskanear a subduction zone.
30 Critical ThinkingOn Earth, clay minerals are the most common products of weathering. Samples from the Moon do not contain any clay minerals. Why?Why are some granite bodies extensively jointed, while others are essentially joint free?
31 Critical ThinkingOn Earth, clay minerals are the most common products of weathering. Samples from the Moon do not contain any clay minerals. Why?Why are some granite bodies extensively jointed, while others are essentially joint free?