Chapter 17 Introduction Stream any channelized body of running water Channel An elongate depression or trough Draining the Land Where water comes from Earth is the only planet in the Solar System that currently holds flowing streams Rainfall fills a stream When it overflows an outlet is formed This then becomes part of a stream which flows to oceans etc Downcutting Process of eroding or digging into substrate Depends on Velocity of flow strength of the substrate and the amount of vegetation cover Drainage Network Interconnecting streams Discharge and Turbulence Discharge The amount of water a stream carries Different streams have different average discharges o But this is difficult to calculate Thalweg Deepest part of a channel The Work of Running Water How does a stream erode Scouring loose fragments of sediment Breaking and Lifting Abrasion grinding the walls of the stream Dissolution running water dissolves soluble minerals Streams transport loads by Dissolved Load Dissolved soluble minerals Suspended Load Tiny grains that swilr along with the water and never touch the bed Bed Load Large particles that bounce up and down off the bed How Do Streams Change Along Their Length Streams progressively deepen their channels by downcutting But the lowest elevation a stream can go is the base level The Evolution of Drainage become erased Over time landscape changes and leads to the drainage of rivers causing them to Stream Piracy Erosion caused a stream to intersect another Superposed Streams Streams that have a preexisting geographic layout Antecedent Streams Existed before the range uplifted Raging Waters the stream channel A flood occurs when the volume of water flowing down a stream exceeds the volume og Flash Flood When stream water overflows too quickly for anyone to react and escape The largest floods occurred during the Ice Age They were referred to as megafloods Floodways Areas that are more likely to be flooded Rivers A Vanishing Resource Rivers are disappearing due to Pollution Dam Construction Overuse of Water The effects of Urbanization and Agriculture on discharge Chapter 18 Outline 1 Water covers 70 8 of Earth s surface 2 Land along the coast a Where 60 of the population lives in the world 3 Cartographers divide the ocean into parts with different volumes and boundaries a Northern Hemisphere contains 81 of the continental crust b Clear images of ocean floor bathymetry i Variation in depth based on sonar measurements and satellite c Continental Shelves i Shallow portion of ocean 500m ii Past the shelf abyssal plain 1 4 4 5km down iii Passive continental margins 1 Margins that are not plate boundaries 2 Occurs after plates break in two and rifting stops occurring iv South America Active continental shelf 1 Plate boundary with many earthquakes 2 Convergent plate boundary at Pacific side of S A d Submarine Canyons Narrow deep boundaries i Dissect Continental shelves and slopes ii Some at mouths offshore of major rivers iii Erosion of submarine canyons result from turbidity currents avalanches of sediment e Faulting causes distinct features i Strike slip fracture zones ii Transform link segments of a ridge iii Subduction deep trough trench bordering volcanic arc iv Divergent plate boundary Mid ocean ridge 4 Pelagic sediment covers basalt of oceanic crust a Plankton shells and clay i Accumulates on old parts further away from MOR 5 High points around hot spots if they protrude to surface Oceanic islands a Island normally submerges due to erosion and slumping i Forms sea mount ii If it submerges after being overgrown by a reef and has a flat top will form a Guyot 6 Ocean water is less dense than fresh because of increased salinity a Different salinities with depth halocline 7 Ocean temperature varies with latitude based on different amounts of solar radiation 8 Ocean has currents Surface and deep currents a Interactions of sea and wind i Sometimes forms eddies ring shape currents ii Wind shear on water doesn t parallel wind 1 Caused by Coriolis effect 2 N Surface currents to veer towards right 3 S Currents to the left iii Gyres North 1 Clockwise currents in large circular flow patterns in 2 Counterclockwise in south 3 Caused because of ocean basins and surface currents 4 Center aka North Atlantic Sargasso sea seaweed sluggish water iv Upwelling downwelling deep currents 1 Downwelling upwelling caused by lack excess of water on an opposite side of the sea 2 Can also be caused by salinity and temperature a Rising and sinking of water Thermohaline Circulation 3 Vertical movement of sea tide Intertidal zone broad tidal flats a b Tide generating force Gravitational attraction of the moon and centrifugal force caused by revolution of the earth moon i Bulges in ocean water causes lack more water on opposite of earth tides c Tilt of earths axis tides are never the same size d Moon s orbit i 28 days tides are 50mins later each day e Sun s gravity i Extra low tides neap tides Suns pull counteracts moon s ii Extra high tides Spring tides opposite sun works with moon f Focusing effect of bays i Flood tide brings extra high tide because of large volume of water in a small area g Basin shape sloshing water with tides i Add subtract to global tide bulge ii Can affect rhythm of tides h Air Pressure i When air pressure drops sea surface rises ii Adds to storm surge 4 Due to the friction of the tides and movement of the moon across the earth days slow at 002 seconds a century v Wave action 1 Wavelengths greater towards surface smaller below a Submarines travel below the wave base travel smoothly 2 Rogue waves wind currents focused and cause high waves at least 2x of normal waves 3 Breakers water is shallower friction causes bottom of wave to move slower than top top curves over the base until it crashes onto shore 4 Swash upward surge onto beach 5 Backwash gradually draws water back to beach 6 Waves make a large angle with the shoreline but bend on approach to shore Wave refraction no more than 5 degrees from shore 7 Longshore Current backwash flowing back to ocean flows parallel to beach 8 Rip Current perpendicular flow of water back to the ocean caused by excessive water rushing back 1 Beach Face steeper concave part of the foreshore zone of a beach caused by a lot of swash 2 Berms Areas that receive sediment during super high tides or storms vi Beach profile 3 Beach Drift drift of water to move sand across hundreds of KM across a beach beach drift a Sandspits just out in front of a bay
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