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Rain & Streams Homework 3: Due Wednesday

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Rain & Streams Homework 3: Due Wednesday EESC 2200 Homework 3: The Solid Earth System Due Wednesday Rain & Streams 6 Oct 08 Global Near-surface Water Budget What about the solid Earth?? H2O H2O H2O H2O H2O 100 -1000 ppm H2O in mantle H2O 27 4 x 10 g mantle Return of Water to Mantle 23-24 4 x 10 g H2O in mantle 24 1.4 x 10 g H2O in ocean 0.5 - 3 oceans in mantle! The Hydrologic Cycle 108,000 km3/year precipitated on land 46,000 km3/year transported on shore 62,000 km3/year evaporated from continental reservoirs 46,000 km3/year runoff to oceans What drives wind? Sun energy radiated hottest + Coriolis Global at equator "force" circulation Vertical Circulation cool, dry heating cooling, rain warm, wet hot, dry hot, dry 0° 30°N 30° S Latent Heat •Evaporation absorbs heat •Condensation releases heat H2O in atmosphere stores latent heat Saturation of ascending air w = water content a = capacity function of temperature % humidity = (w/a) x 100% w a T dewpoint = T of saturation Adiabatic Uplift dry wet T • As air rises, it expands • Conserve energy: temperature drops H2O released when cools to saturation World’s Deserts Rain shadow effect (Hawaii) Wet (East) side of Hawaii Dry (west) side of Hawaii Streams: The Geology of Running Water Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Streams are vital geologic agents • They carry most of the water that goes from land to sea • They transport billions of tons of sediment to the ocean each year • They transport billions of tons of soluble salts to the oceans each year • They shape the surface of the Earth A stream Geologist's Definition: • water flowing downhill • clearly defined passageway • transports sediment • natural ES101-19a Anatomy of a Stream passageway = channel ES101-19a The Lower Mississippi floodplain ES101-19a Flood Plain channel floodplain ES101-19a Main features of an alluvial valley Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Anatomy of a Stream channel water discharge = volume flow per time interval (m3/s) ES101-19a ES101-19a Discharge of Merrimack River ES101-19a Anatomy of a Stream channel discharge = solids and load * Future dissolved matter sediments? transported ES101-19a Discharge includes • most of Ocean's water supply (~90%) The load includes Sediment supply to the oceans other other dissolved clastic 1% 10% rivers rivers clastic dissolved 70% 19% from Taylor and McLennanES101-19a In cross-section, channel shapes vary Aberjona Charles Hudson width >> depth high discharge ES101-19a Fast-Moving River high gradient Slow-Moving River low gradient Stream Gradient Colorado River Vertical Distance Horizontal Distance ES101-19a Stream Gradient going downstream, gradient decreases Colorado River 3000 Elev., m 0 4000 2000 0 distance from mouth, km ES101-19a Base Level The ability of a stream to erode is based on velocity of water. Velocity is proportional to slope. At a sufficiently low slope, streams will run without eroding: this is called the base level. The ultimate base level is sea level, although local base levels exist, since flow paths are seldom one consistent slope. Forms of Channels • Straight (rare) • Meanders • Braided ES101-Lect 19b Meandering Streams Oxbow lake Point bar Cut bank Fig. 10.12 Meandering Streams Channels rarely straight momentum straight pushes out against bank water in main flow pushes outward ES101-Lect 19b With time, meanders grow hi-V, erosion deepest flow lo-V, deposition (this erosion, deposition creates landscape) ES101-Lect 19b ...and deposit sand bars on inner sides... cutbank point bar ES101-Lect 19b ...meanders grow to high curvatures... high V, erosion A' low V, deposition A high-V A' A ES101-Lect 19b ...eventually, oxbow lakes can form oxbow lake cutoff migrates downstream ES101-Lect 19b Flow also controls cross-sectional shape A B A' B' A A' B B' pool submerged barES101-Lect 19b Braided Streams Braided Streams • deposition in middle of stream -> divided channel • high energy, high sediments • highly variable discharge e.g. below glaciers ES101-Lect 19b Meanders: Low gradient, fine sediment Braided: Variable discharge, large sediment load ES101-Lect 19b Watersheds Every stream is defined by an area on the ground where incident precipitation will all flow into that stream. These drainage basins or watersheds are separated by topographic highs: divides. The Continental Divide Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water What controls divide location? • Tectonics creates topography • As mountains evolve, streams follow... W divide E Pacific Atlantic Drainage Drainage South American Andes ES101-Lect 19b Drainage Patterns The topographic pattern streams take are not necessarily totally random. They are affected by rocks and their structures. DrainageDrainage EvolutionEvolution Superposed streams – Cross deformed terrain ignoring structure. Streams initially develop in younger, flat strata. The stream then chainsaws into underlying rocks. Stream maintains its initial geometry. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water DrainageDrainage EvolutionEvolution Antecedent drainages. Tectonic uplift may raise ground beneath established streams. If erosion keeps pace with uplift, the stream will cut through the uplift. Called antecedent drainage. If the rate of uplift exceeds erosion, the stream is diverted by the range. Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 17: Streams and Floods: The Geology of Running Water Mississippi Floodplain These are satellite images before and during Summer, 1993 floods of the Mississippi river north of St.Louis. River Hydrograph discharge vs. time Flood Discharge after a storm “Predicting” the frequency and magnitude of floods Floods and Urbanization surface runoff vs. infiltration natural land cover vs. urban area .
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