1GY 301: GeomorphologyGY 301: GeomorphologyLecture 7: Coastal Plain Topography:TerracesUNIVERSITY OF SOUTH ALABAMALast TimeCoastal Geomorphology 1Basic classification (substrate and “energy”)Processes (waves and currents)Topographic Features (lab prep)Coastal GeomorphologyThere are two main controls on coastal geomorphology:1) Geological materials available on the shoreline●Outcrop (rock)●Gravel●Sand●Mud2) “energy” of shoreline●waves●currents●tides●stormsCoastal GeomorphologyAlthough diverse, you can group most shorelines into one of 3 broad types:1) Rocky (high energy [waves, tides, currents]; outcrop/rocks)2) Beaches (high energy [waves]; sand and gravel)3) Estuaries (low-high energy [tides]; mud)Bay of Fundy, CanadaRocky CoastlineThe irregular shape of rocky coastlines is a consequence of wave refraction; the bending of waves as they approach a shoreline. Waves tend to bend toward headlands which focuses strong erosive forces around their periphery.Sandy ShorelinesFrom Walker, R.G. and James, N.P. (1992). Facies Models: Response to Sea Level Change. Geological Association of Canada, 409p.They come in many forms:●Barrier Islands●Spits●Strandlines●Beaches (open/sheltered)2Sandy ShorelinesWave refraction will result in longshorecurrents and longshore driftToday’s AgendaCoastal Geomorphology 2: Terraces Some definitions and types of terracesTerraces on topographic mapsSea level changes and terrace developmentCoastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Tuffa/Sinter Terraces:silica (opaline) precipitated from hot water in hydrothermal pools/geysersTuffa deposits at Yellowstone National ParkCoastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Tuffa/Sinter Terraces:silica (opaline) precipitated from hot water in hydrothermal pools/geysersPink Terraces, Tawawera, New Zealand (c. 1890) Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Beach Terraces:Sediment deposited at the high and/or low tide levels in beach environments3Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Beach Terraces:Sediment deposited at the high and/or low tide levels in beach environmentsHigh tide terrace, shingle beach, Canterbury, New Zealand Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Beach Terraces:Sediment deposited at the high and/or low tide levels in beach environmentsLow tide terrace, Banks Peninsula New Zealand Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Glacial Terraces:Sediment deposited primarily by melt water or behind ice-dams in glaciated environmentsGlacial outwash, Northern Canada Coastal TerracesGlacial Terraces: Sediment deposited primarily by melt water or behind ice-dams in glaciated environmentsGlacial outwash, Northern Canada Coastal TerracesGlacial Terraces: Sediment deposited primarily by melt water or behind ice-dams in glaciated environmentsGlacial outwash, Northern Canada Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)Stream bed model; channel incised river terraceRiver terraceRiver terraceChannelRiver Terraces:Sediment deposited primarily on flood plains of rivers. Directly related to base level.4Coastal TerracesTerraces: relatively flat plains formed by deposition or less commonly, by precipitation (hydrothermal processes)River Terraces:Sediment deposited primarily on flood plains of rivers. Directly related to base level.Two river terraces, United KingdomCoastal TerracesBase level: The lowest level that a river can erode down to (incise). It is controlled by the elevation of water bodies that the river flows into.DamCoastal TerracesBase level: The lowest level that a river can erode down to (incise). It is controlled by the elevation of water bodies that the river flows into.DamBase LevelCoastal TerracesBase level: The lowest level that a river can erode down to (incise). It is controlled by the elevation of water bodies that the river flows into.DamBase LevelBase LevelVertical exaggeration = 50XCoastal TerracesSea level is the ultimate base level……Coastal TerracesSea level is the ultimate base level………… and it is nevertruly constant5Coastal TerracesSea level is the ultimate base level………… and it is nevertruly constantTransgressionBase level risesCoastal TerracesSea level is the ultimate base level………… and it is nevertruly constantRegressionBase level fallsCoastal TerracesConsequently, different terraces can be deposited at different elevations over time.Two river terraces, United KingdomCoastal TerracesConsequently, different terraces can be deposited at different elevations over time.Coastal TerracesThere is one more variable in the terrace equation that must be recognized: upliftTectonically active areas may rapidly elevate and rotate terraces.Uplifted beach terrace, Wanganui New Zealand Coastal TerracesThere is one more variable in the terrace equation that must be recognized: upliftTectonically active areas may rapidly elevate and rotate terraces.Uplifted river terraces, Central Asia6Coastal TerracesThere is one more variable in the terrace equation that must be recognized: upliftBut this is good! It allows us to synchronize world-wide eustatic events.Coastal TerracesLate Pleistocene-Holocene sea level curve Coastal TerracesC14dating and other techniques are used to establish the age of each terraceTerraces on Topographic MapsWeeks BayWest to east cross-section across Weeks BaySchematic, no vertical scale impliedWest East6000 yrs B.PCitronelle Fm.(Tertiary)“Ecor Rouge” Fm. (Tertiary)TerracesX XI IX XIII XIV XV3 km>39,000 yrs B.PTerraces on Topographic Maps7Terraces on Topographic MapsTerraces on Topographic (& Geological) MapsUpcoming StuffHomeworkFinish lab 3 (due Friday)Next Lecture: GIS and planning (& maybe environmental applications)Friday’s Lab: See homework