Erosion and Landscape EvolutionHow Do We Know Rivers Cut Their Valleys?Constructive and Destructive ProcessesStream Abrasion, Marathon CountyStream Potholes, Marathon CountyMega-Potholes, St. Croix ValleyAnatomy of a Drainage SystemThe Continental Divide, ColoradoStream OrderThe River That Did This….Looks Like This Near Its SourceSlide 12The Ideal Stream Cycle (W.M. Davis, 1880)YouthYouthful Landscape, ArizonaMaturity (Early)Young-Mature Landscape, CaliforniaMature Landscape, KentuckyMaturity (Late)Old Mature Landscape, TennesseeOld AgeMonadnock, ColoradoMonadnocks, MaineOld Age Landscape, South AmericaThe Onset of Old Age? IndianaOld Age? Or Maybe Not: NebraskaOld Age? No! (Wisconsin)RejuvenationRejuvenation, UtahRejuvenation of an old-age landscapeRejuvenation, San Juan River, UtahRejuvenation of an early mature landscapeMachu Pichu, PeruSlide 34Why the Stream Cycle Doesn't Explain EverythingSea Level and River ProfileSuperposed (Antecedent) Drainage Streams Cut Right Through High Topography Rejuvenated Peneplain: the Northeastern USRejuvenated PeneplainSuperposed Drainage, Delaware Water GapWater Gap, PennsylvaniaCumberland Mountains, VirginiaCumberland GapDevil’s Gap, WyomingApproach to Devil’s GapRivers and Crustal Movement, CaliforniaTectonic Uplift, ColoradoTectonic Uplift, Grand CanyonThe Ultimate Antecedent Drainage, India-Nepal-TibetDrainage DiversionThe Huang He: “China’s Sorrow”River Diversions in the Caspian RegionStream Piracy: Northeast EnglandWhy is the Danube Blue?Piracy on the DanubeFlood, EcuadorFlood, Green Bay, June 1990Slide 58Building Smart in a Flood PlainChanneled Scablands, WashingtonFluid Flow is Scale-InvariantErosion of Bedrock River BedsScabland Terrain, OregonErosion of Soft River BedsMega-Gravel Bar, WashingtonMega-Flood Deposits, WashingtonErosion and Landscape EvolutionHow Do We Know Rivers Cut Their Valleys? John Playfair, 1800•Tributary valleys almost always join the main valley at exactly the same elevation, even though the valleys may begin many miles apart. This is very unlikely unless the rivers have cut the valleys.•How Rivers Widen ValleysConstructive and Destructive Processes Highlands•Erosion Dominates •Destructive Processes •History not Preserved •Little Geological Record TransportLowlands, Coastal Plain, Lakes and Seas•Deposition Dominates •Constructive Processes •History Preserved •Good Geological RecordStream Abrasion, Marathon CountyStream Potholes, Marathon CountyMega-Potholes, St. Croix ValleyAnatomy of a Drainage SystemThe Continental Divide, ColoradoStream OrderThe River That Did This….Looks Like This Near Its SourceThe Ideal Stream Cycle (W.M. Davis, 1880)Not a Literal Time Sequence•Youth •Maturity •Old Age •RejuvenationYouth •V-Shaped Valley •Rapids •Waterfalls •No Flood Plain •Drainage Divides Broad and Flat, Undissected by Erosion •Valley Being Deepened •General Agreement on this stage, lots of examplesYouthful Landscape, ArizonaMaturity (Early) •V-Shaped Valley •Beginnings of Flood Plain •Sand and Gravel Bars •Sharp Divides •Relief Reaches Maximum •Valleys stop deepening •General Agreement on this stage, lots of examplesYoung-Mature Landscape, CaliforniaMature Landscape, KentuckyMaturity (Late) •Valley has flat bottom •Narrow Flood Plain •Divides begin to round off •Relief diminishes •Sediment builds up, flood plain widens •River begins to meander •Many geologists believe slopes stay steep but simply retreat.Old Mature Landscape, TennesseeOld Age •Land worn to nearly flat surface (peneplain)•Resistant rocks remain as erosional remnants (monadnocks)•Rivers meander across extremely wide, flat flood plainsMonadnock, ColoradoMonadnocks, MaineOld Age Landscape, South AmericaThe Onset of Old Age? IndianaOld Age? Or Maybe Not: NebraskaOld Age? No! (Wisconsin)Rejuvenation •Some change causes stream to speed up and cut deeper. –Uplift of Land –Lowering of Sea Level–Greater stream flow• Stream valley takes on youthful characteristics but retains features of older stages as well. •Can happen at any point in the cycle.Rejuvenation, UtahRejuvenation of an old-age landscapeRejuvenation, San Juan River, UtahRejuvenation of an early mature landscapeMachu Pichu, PeruMachu Pichu, PeruWhy the Stream Cycle Doesn't Explain Everything•Rises and falls in sea level during the ice ages rejuvenated most landscapes to some extent. •Climate changes mean that mass-wasting processes in temperate regions may have undergone radical changes repeatedly in the last few million years. •In places where conditions have remained uniform for long times, like the stable interiors of Africa, Australia and South America, the ideal stream cycle seems to work best.Sea Level and River ProfileSuperposed (Antecedent) DrainageStreams Cut Right Through High TopographyRejuvenated Peneplain: the Northeastern USRejuvenated PeneplainSuperposed Drainage, Delaware Water GapWater Gap, PennsylvaniaCumberland Mountains, VirginiaCumberland GapDevil’s Gap, WyomingApproach to Devil’s GapRivers and Crustal Movement, CaliforniaTectonic Uplift, ColoradoTectonic Uplift, Grand CanyonThe Ultimate Antecedent Drainage, India-Nepal-TibetDrainage DiversionThe Huang He: “China’s Sorrow” •1887: 2,000,000 dead •1931: 3,700,000 dead •1938: The Chinese dynamite levees to slow the Japanese; half a million Chinese died.River Diversions in the Caspian RegionStream Piracy: Northeast EnglandWhy is the Danube Blue?Piracy on the DanubeFlood, EcuadorFlood, Green Bay, June 1990Flood, Green Bay, June 1990Building Smart in a Flood PlainChanneled Scablands, WashingtonFluid Flow is Scale-InvariantErosion of Bedrock River BedsScabland Terrain, OregonErosion of Soft River BedsMega-Gravel Bar, WashingtonMega-Flood Deposits,