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Running Water 1) The Hydrologic Cycle: The circulation of water between the hydrosphere, solid earth, and atmosphere. Powered by the sun 97% of the Earth’s water is in the ocean 2) Streams and rivers Water is sourced mainly from groundwater and surface runoff a) Surface runoff Drainage Basins: an AREA that collects water to supply streams Drainage Divides: high places that separate drainage basins Longitude Profiles: shows slope, view from head to mouth b) Base level and graded streams Two general types of base level Ultimate: the ocean Local/temporary: waterfall, dam Raising base level causes deposition Lowering base level causes erosion Graded Streams: Maintain the exact velocity required to transport materials and neither erode or deposit. A natural state for streams c) Transport of Sediment by Streams Capacity amount of material a stream can carry Competence the largest size material that is carried Dissolved load Material dissolved in the water Supplied mostly by groundwater Suspended load Carries largest amount Sand, silt, and clay Velocity decides what size material will be carried and what will be deposited Bed load Largest material Bounces along the bottom Only moves when water is forceful d) Deposition of Sediment by Streams Stream sediments Generally well sorted Stream sediments are known as alluvium Velocity separates the particles by size (sorting) Bars: sand and gravel deposited in a channel. Alluvial fans: Intermittent streams depositing large amounts of sediment onto a valley floor in the shape of a fan Common in deserts Deltas: Formed when a stream or river enters a body of water with lower energy, and deposit its sediments Can produce large volumes of coarse sediment Great Oil and Gas Reservoirs Ex: Gulf of Mexico Floodplains: Valleys that flood from meandering streams Consist of silt, sand and gravel Large flat areas plains with multiple old stream channels Sediment deposited during the formation of floodplains create natural levees e) Stream Valleys Narrow V-shaped: Niagara Falls Higher gradient Farther from base level Rapid down-cutting in resistant rocks Rapids and waterfalls (young features) are common Vertical walls More vertical erosion Wide valleys: meandering streams like Miss. River Lower gradients Closer to base level Mostly in a single channel with few islands Has raised edges called levees. More forceful side to side meandering Meandering streams flow on floodplains Terraces form when river has adjusted to a relative drop in base level by downcutting Point bars: deposition on inside edge of meander Cut banks: outside edge of meander-erosion Cutoff meander: cut through a meander and connect with another part of the stream Oxbow lake: An abandoned meander, it eventually fills with sediment and becomes a meander scar. f) Stream Process and Response i) Uplift of land/Elevation of mouth falls Increases gradient and stream flow Stream starts to erode: both headward and downward to bedrock Stream terraces: create new floodplain level Stream piracy: erosion into current channel and steals its flow. ii) Elevation of mouth rises Decreases gradient and stream flow The stream starts to drop sediment in its channels and on floodplain during floods Results in wide flat-floored floodplain valleys Groundwater One of the most valuable resources About 1% of freshwater is underground Largest supply of freshwater 1) Distribution of Underground water Groundwater generally accumulates in sedimentary basins It flows in response to gravity It moves very slowly, feet per year It is easily contaminated and difficult to cleanup 2) The Water Table Zone of Aeration Area above the water table Lots of water, but hard to collect because of how it attaches to rocks and soil Zone of Saturation Below top of water table Completely saturated Varies seasonally due the quantity, distribution, and timing of precipitation Streams interact with the groundwater system Gaining streams Streams that gain water from groundwater Losing streams Streams that lose water to groundwater 3) The Storage and Movement of Groundwater Porosity Percentage of void space in rock and sediment Stores fluid Permeability The ability to transmit water through the pores of sediment or material Aquitards The layers of material that prevent water flow Aquifers Sediments or material that transmits water freely a) Movement of Groundwater Very slow Its caused by gravity It moves from high water table zones to low zones Springs Where the water table meets the Earth’s surface Wells Most common way of retrieving GW Used for agriculture, and drinking water Wells must break through the water table When the water table is lowered away from the well, its called drawdown; this results in a cone of depression Artesian Wells Wells that flow to the surface Water rises above the top of the aquifer An aquitard must both be present Hot Springs Hot Springs that have a much warmer water temp than local air temp. Water is heated by circulating deep in the Earth 4) Problems Associated with Groundwater Withdrawal Water table height is effected by amount of water going into and coming out of aquifer Severe droughts and over usage of wells can cause long term decreases in water table height Subsidence: GW removed more that replaced, it can cause the ground to sink GW contamination and cleanup Point or non-point sources Subsurface mobility of chemicals Toxicity of chemicals: how are levels determined? Glaciers Form when more water is frozen than melts each year Water is stored in glaciers for long periods of time 2% of the earth’s water is in glaciers If all glaciers melted, sea level would dramatically rise Glaciers are a strong erosional force, like a bulldozer 1) Types of Glaciers a) Valley (alpine) glaciers Slow moving glaciers located in old stream valleys Ice bound by rock walls that flow from an upward point These form many features of classic glacier landforms b) Ice sheets Much larger than valley glaciers Two currently exist N. Pole/Greenland and Antartica Flow into ice shelves: flat masses of ice that extend toward the sea c) Other types of glaciers Ice caps Small ice sheet glaciers, that cover upland and plateaus and bury landscape Outlet glaciers Flow from ice caps and ice sheets outward through mountains toward the sea. Like localized valley glaciers dumping into sea Piedmont glaciers When valley glaciers merge at base of large mountains 2) Movement of a Glacier a) Two types of flow Plastic flow Movement within ice Basal slip Mass of ice slips along ground Melted water causes ice to move over rock Caused by heat from in the earth b) Zone of Fracture Does not flow, is brittle and cracks Forms crevasses from glacier moving over rough terrain c) Rate Some glaciers move at unnoticeable rates (cm/day), while others move up to several meters a day Quick movements by glaciers are called surges d) Zone of Accumulation Area defined above the snowline Where ice and snow collect and form e) Zone of Wastage Located generally below snowline Where glaciers lose ice and snow due to melting Ice can break off in a process called calving which produces icebergs f) Glacial budget Balance between zone of wastage and accumulation If budget is positive glacier grows, if not glacier shrinks 3) Glacial Erosion a) Plucking Water flows into cracks of rocks and freezes Glacier lifts, picks up and moves rocks Can move very large rocks b) Abrasion Caused by rock movement sliding over rock, “sanding” it down Produces rock flour and glacial striations 4) Landforms created by Glaciers Glacial regions have U-shaped valleys with steep slopes Glaciers generally flow along previously existing streams Glacial trough: U-shaped valley Hanging Valleys: Above a glacial trough, after glaciers move away. Truncated spurs: Triangular shape, where a ridge meets a glacial valley Pater noster lakes: String of lakes formed after glacial retreat in a glacial trough. Created by plucking. Cirque: Bowl shaped, terminal head of glacier valley Tarn: Small lake located at base of cirque, created from plucking. Fiords: Steep sided inlets in the sea. Caused from submerged glacial troughs and sea level rising Aretes: Sharp sided ridges that line glacial valley. Horns: Cirques grouped around a point. Sharp pyramid shaped peaks (Like Matterhorn at Disneyland). 5) Glacial Deposits Glacial Drift: The sediments deposited by glaciers. Two types: Till and Stratified drift a) Glacial Till Sediment deposited when ice melts. Melting ice can’t sort sediments. Characterized by very poorly sorted, polished and scratched sediments. Moraines Lateral moraine: Ridge formed by till on outside edge of glacier Medial moraine: Formed by two lateral moraines when glaciers merge together End moraine: Ridge of till that marks the former spot of the front of a glacier. Ground moraine: Layers of till in areas where ice moves away Drumlins: Elongate parallel hills covered by ice sheets Composed of till, found in groups, or drumlin fields Glacial Erratic: Large rocks or boulders free lying that originate from elsewhere b) Stratified Drift Sorted from glacial melt water according to shape and size Layered and better sorted than till Consists mostly of sand and gravel i) Outwash plain Large sloping surface created near the edge of end moraines Called a valley train when limited to a valley ii) Ice-contact deposits Sediment deposited underneath melting ice by melt water Kames: Hills created underneath melting ice by melt water Eskers Large ridges of sediment following streams underneath melting ice by melt water 6) Glacial Theory and the Ice Age Last ice age was about 18,000 years ago Climate changes come from variations in the earth’s orbit and tilt of the axis Deserts 30% of earth’s land is made up of dry regions 1) Two dry land types Deserts Lacks water Very dry Generally defined as less than 10” of precipitation per year Steppe More humid, semiarid Transition between desert and more moist areas Acts as a border area between desert and other climates, can be from a rain shadow. a) Low latitude deserts (30 degrees N and S of EQ) Near Tropic of Cancer and Capricorn High pressure and wind circulation are responsible for dry climate b) Middle latitude deserts Far from ocean Mountains around keep moisturized air away Can be from a rains shadow Area resulting in less moisture and cloud formation 2) Geologic Processes in Arid Climates Mostly mechanical weathering Waters role in deserts Water is responsible for most desert erosion Contain ephemeral streams, only flow after heavy rainfall Floods more common because lack of vegetation and dryness prevent water from soaking into the land 3) Transportation of Sediment by Wind Different from water Density of wind is lower than water Wind spreads over large areas, not just channels Bed load Mostly sand Moves (skips) along surface through a process called saltation Suspended load Made up of silt and clay Can be carried much farther and higher into the atmosphere a) Wind Erosion Deflation Lifts and removes loose material Create blowouts Layer of pebbles and small rocks that are too large to be moved by the wind is called desert pavement Abrasion Wind sands down rocks Creates uniquely shaped rocks called ventifacts Ventifacts are rocks that are polished and shaped by wind 4) Wind Deposits Dunes Sand deposited in the shape of a mound or ridge Slope on the sheltered side is very steep; windward side has a gentler slope Layers that form on the steep side are called cross beds Types of sand dunes Barchan Solitary, U-shaped with tips pointing downwind Form where there is limited sand, flat with little vegetation Transverse Long ridges perpendicular to wind Largest dunes: up to 200m high, 1-3 km across, 100’s of km long Steady wind lots of sand and little vegetation Longitudinal Long ridges parallel to wind Up to 100m high, can be 100’s of km long. Moderate sand with changing winds Star Variable wind, star shaped. 5) Terms: Bajada: coalescence of alluvial fans at base of a mountain Playas: flat central area of an undrained basin Playa lakes: temporary lake in playa Inselbergs: isolated mountain peaks from late stage erosion in a desert Shorelines Boundary where different systems interact together Waves and currents change the features of the coastline Moves and deposits sediment along coast Coastal landforms are delicate, short-lived features 1) Waves Terms Crest: top of wave Trough: separates crests Wavelength: horizontal distance between crests Period: time between crests Wave height: measured between crest and trough Wave period and wave energy Longer wave periods have much higher energy and higher open ocean velocities Stronger, longer duration storms produce longer period waves. 2) Longshore Transport When waves meet the shore at an angle Transports sediment in a zigzag pattern along the beach with longshore current Longshore transport can move large amounts of sand along the shoreline In San Diego its strongly to the south in the winter and slightly north in the summer 3) Shoreline Features a) Erosional Wave-cut sea cliffs Sea cliffs form along the shoreline from wave erosion With time sea cliffs migrate landward and grow in size Wave cut platforms Slightly seaward sloping surface cut in surfzone These become uplifted and exposed on emergent shorelines Common in San Diego and on the California Coast Sea arch Form at headlands where 2 sea caves that come together from different sides Perforate through headland Sea stack Form when a sea arch fails Mound of rock and debris that eventually is taken to sea by waves Common on the West Coast b) Depositional Spits A deposit of sediment normally formed from longshore current deposition where the water goes from high energy to low energy Ex: Santa Barbara Harbor Bay-mouth bar A sandbar that stretches across a bay, separating it from the ocean Tombolo A low energy zone is created by a structure, and island, a breakwall etc. and sediment get deposited behind it. Barrier islands Ridges of sand that run parallel to the coast Common on submergent coasts Ex: East Coast 4) Shoreline Erosion Problems Most erosion occurs during storms with larger longer period waves Large waves break against rocks and sea cliffs, etc. The waves undercut cliff and it fails Rock fall if the rocks are hard and cliffs are near vertical Slump if the sediments are soft and sloping Types of shoreline protection Breakwaters Structures used to protect boats from large waves. Protects and builds beach in front of breakwall Seawalls Seawalls are built up against sea cliffs to protect land structures and sea cliffs from large waves. Beach nourishment Adds large amounts of sand to the beach to keep water away from sea cliffs Raises beach sand level Jetties and groins Are used to trap and buildup sand Increases deposition on upcurrent side and increases erosion on downcurrent side 5) Emergent and Submergent Coasts Another important factor in understanding shorelines is tectonic activity A) Submergent Sea level rises or land sinks down Contain estuaries and barrier islands East Coast is an example B) Emergent Land rises or sea level drops Forms marine terraces, sea cliffs, and sea caves California is an example 6) Tides Daily change in ocean elevation From gravitational attraction of the moon and sun Spring tides create the largest range during new/ and full moons Neap tides create a smallest tidal range, during 1st and 3rd quarters moons 7) Tsunamis Formed by rapid displacement of seawater from an earthquake, landslide (or underwater), or volcano. Usually less than 2 feet in the open ocean. Long wavelength, commonly 100’s of miles. Undetectable by ships in open ocean Open ocean velocity is 400 – 500 mph. About 4-5 hours from Alaska to San Diego (or Hawaii). Wave stacks up on continental shelf, ½ of the time trough arrives first. Waves 30 – 100 ft are common Highest seismic seawave is thought to be 300 ft., 66 million years ago in the Gulf of Mexico Energy and Mineral Resources 1) Mineral Resources a) Mineral resources and igneous processes: Metals such as gold, silver, copper, mercury, lead, platinum and nickel can come from igneous processes Hydrothermal solutions Formed from circulating warm, metal and mineral-rich water heated by late stage magmas. Usually associated with sulfide minerals Commonly found: gold, silver, and mercury. Can be in concentrated veins or a disseminated distribution. Magmatic segregation: Separation of magma due to crystal settling and deposition Layered intrusives Very rare Sedimentary features found in magma chamber Stillwater Complex in Montana has most of the free worlds platinum. Ex: Stillwater and Bushfeld complexes: Diamonds Found in Kimberlite pipes Located in very tightly controlled areas. Monopoly by DeBeers a Dutch company. Graded by color, cut, size and clarity. Pegmatites: Crystallize in a fluid-rich late stage of granitic magmas Large crystals of quartz, feldspar, muscovite, hornblende and other exotics b) Mineral resources and metamorphic processes Two types that rocks can undergo, contact metamorphism and regional metamorphism The most common mineral deposits are formed by contact metamorphism where hot fluids generate sulfide deposits associated with metal ores such as zinc, lead, copper, and iron. See above section in igneous rocks. Regional metamorphism can have larger areas of high metamorphic facies. This can produce minerals form in these higher metamorphic ranges such as garnets etc. c) Placer deposits Deposition in a stream or river where heavy (high specific gravity) material settles after being carried downstream in the current of the river or stream. Placer minerals can be gold, tin, diamonds, and tungsten minerals. d) Nonmetallic mineral resources Resources made from nonmetallic minerals include things like: Building materials: sand and gravel aggregates, gypsum, plaster, wallboard etc. Industrial minerals: garnets, diamonds, sulfur, salt etc. b) Fossil fuels Formed from the organic remains of (mainly) plants Non-renewable energy source Provide the majority of the world’s total energy demands i) Coal Accounts for about 20% of nation’s energy needs Burning coal produces sulfur dioxide, an acidic gas that contributes to the formation of acid rain ii) Oil Easier to get out of ground and cheaper to transport than coal Environmentally hazardous to transport USA is dependent on foreign sources of oil, we import 50% of the oil we use iii) Natural gas Provides around 20% of the world’s consumption of energy Very clean burning Burnt in power stations Used by many people to heat their homes Easy to transport along pipes USA has large reserves and is self-sufficient on natural gas