TEST 4 REVIEW Rivers Distribution of Water Oceans 96 Glaciers 1 Groundwater 1 Hydrologic Cycle Water into streams Stream Profile Sheetwash Thin covers surface Downcuts Sheetwash becomes concentrated erodes scours out a channel Headward Erosion Fastest downcutting at channel head channel moves upslope tributaries form to feed new stream drainage network develops Types of drainage patterns Controlled by what the water flows over Like the veins of a leaf Flow over uniform 2 Radal 1 Dendritic Surface wheel spokes 3 Rectangular faults right angle joins ridges forms water gaps 4 Trellis Flow from center point mountain or volcano resembles Controlled by grid of fractures as joints or Form in long valleys trunk stream cuts resistant Natural profiles that a Catchment region Which way does the rain go Graded stream All features are steepest near the source of the stream Equilibrium profile Longitudinal stream strives to achieve Base level Lowest elevation a stream bed can reach at a given locality Base Level Changes Lower base level steeper profile increase stream erosion down cut incise Raise base level Shallower profile infill shallow areas deposit sediment Sea level drop Sea level rise uplift decrease Processes involving base level subsidence at mouth uplift at stream head draining of lakes increase Processes involving base level at stream mouth subsidence at head creation of lakes Effects of Changing Base Level Tectonic uplift can significantly change base level and so can changing sea level Incised canyons due to renewed uplift downcutting Downcutting can result in rivers flowing through rugged topography V Shaped Channel Meandering river meandering stream flowing from top of screen to bottom Floodplain Flat topography covered by periodic flooding Common location of farmland as the soil is rejuvenated with each flood Deposition between source and mouth Levees separating river channel from floodplains natural levee bank of sediment built by successive floods up to 6 meters high if levee builds as fast faster than stream bed stream can be above floodplain Levees form when debris laden floodwater overflows the channel and slows as it moves onto the floodplain The Work of Running Water Running water causes erosion in 4 ways Scouring removing loose fragments Breaking lifting snapping off fragments lifting fragments off bed Abrasion grinding action of sand in the water column Dissolution dissolving more soluble minerals Severity of erosion depends on water velocity stream gradient water volume stream discharge sediment content sediment load Most of a stream s erosion occurs during a brief flood Stream Sediments When velocity decreases Sediment grain sizes are sorted by water o Sands are removed from gravels muds from both o Gravels settle in channels o Sands drop out in near channel environments o Silts and clays drape floodplains away from channels The Work of Running Water Sediment load has 3 components Dissolved load mineral ions dissolved in the water typically 100 1 000 parts per million Suspended lead clay to slit sized particles floating in suspension most of the sediment carried by a stream is a suspended load Bed load sand pebble cobble sized material pushed rolled along stream bed water as well as other particles do the pushing Alluvial Semi arid arid areas intermittent streams dump Fans sediment after exiting mountain front Delta Alluvial fan in water COASTAL LANDFORMS Beach Profile 1 Lagoon barrier island 2 Marsh shallow seawater separated from open ocean by wetlands dominated by grasses Backshore between dunes and high tides Intertital between high and low tides Nearshore breakers are high tide level to where wave base intersects sea floor Offshore below fair weather base water depth Nearshore zone may have small submerged ridges bars Bars travel onshore during fair weather offshore in winter Beach Face slopes seaward Slope depends on grain size of bed and wave energy Summertime Beach Produced by light wave activity Wide sandy berm o Swash soaks into beach little backwash erosion Steep beach face Wintertime Beach Produced by high wave activity Narrow rocky berm o Backwash dominates eroding the beach Flattened beach face Beach profile Backshore Berm high flat area height determined by maximum reach of swash Dunes landward margin of many beaches Rest of backshore is dominated by Aeolian wind processes Tidal fluctuations alternately expose and submerge tidal flats Mud and silt dominated Barrier Islands Longshore drift deposits of land parallel to coast o Often provide barrier to storm waves Many formed during rise in sea level following last ice age o With abundant sand supply can build year round bar o As bar lengthens widens traps more and more sand o Above tidal range storms build a berm anchored by Since sea level is rising barrier islands are migrating 18 kya grows more vegetation landward Groin Updrift erosion and downdrift deposition OCEANS The Water Planet 70 Why is there water Outgassing steam from volcanoes comets led to water vapor cooling rain oceans Why is there LIQUID water If Earth were 13 closer to Sun too hot for liquid water If Earth were farther from Sun or less CO2 too cold for liquid water FIVE MAJOR OCEANS Pacific Ocean Atlantic Ocean Indian Ocean Artic Ocean Southern Ocean 81 of land is in N hemisphere Bathymetry mapping of ocean basins has delineated major units 1 Ocean Trenches 2 Continental Margins 3 Ocean Basin Floor 4 Mid Ocean Ridges Deep ocean trench convergent boundaries where lithospheric plates subduct into the mantle long relatively narrow deepest parts of ocean most 8km 11km most are in Pacific Continental Shelf Broad flat from shoreline to continental slope 200 m deep may be 100 s km offshore underlain by continental crust 0 3 degree slope Shallow shelf affected by waves tidal currents o dominant sediments sand nearshore silt mud farther offshore Carbonates occur where little land derived sediment input Continental shelf overlies continental crust Continental slope and rise may overlie the continental oceanic crust transition on passive margins Continental Slope steeper 2 degrees typically mud draped marks edge of continental shelf can extend down to 4 km canyons often dissected by submarine canyons some Grand Canyon often w submarine landslides turbidity currents Continenteal Rise gently sloping sediment apron contourites sands muds deposited from continental slope depths of 4 4 5 km large submarine fans with kms of sediment Abyssal Plain