Intro to Earth Science Reading/Video Notes Quiz 5

Chapter 12, Sections 12.1 and 12.3 (p. 343, 348 - 351)

HERE BEGINS 12.1 Moon hasn't changed much over time, but the Earth HAS! -some changes take millions of years --The Moon's surface remains static because the Moon's outer layer does not consist of moving plates, and because the Moon has no atmosphere, hydrosphere, or biosphere. Therefore, only meteorite impacts or space weathering (the breakdown of minerals due to the impact of cosmic rays) alter the Moon's surface. --The Earth's surface, in contrast, remains dynamic because Earth's outer layer consists of moving plates, and because our planet hosts an atmosphere, hydrosphere, and biosphere. Interactions of lithosphere plates with one another and with the asthenosphere below cause earthquakes, volcanism, mountain building, and basin formation. Movements associated with these phenomena generate slopes down which rocks and sediments can tumble or slide. Meanwhile, chemical and physical weathering, the flow of streams and glaciers, waves, wind, and the activities of life in the Earth System constantly break down and redistribute surface materials. Because Earth is dynamic, it hosts a great variety of landscapes. By landscape, we mean the character and shape of the land surface in a region. The hydrologic cycle (where water molecules move from ocean to air to land and back to ocean) and mass wasting (when gravity transports rock and sediment down slopes) are the energy sources that drive changes in land-surface elevation. A topographic map uses contour lines to represent variations in elevation. -A contour line is an imaginary line on the land surface along which all points have the same elevation. --The elevation difference between two adjacent contour lines on a topographic map is called the contour interval. (contour interval is constant on a topographic map) (perpendicular to line causes changes in elevation) (spacing between contour lines allows one to picture a slope's angle) A topographic profile is the trace of the ground surface as it would appear on a vertical plane that slices into the ground, allows for representing variations in elevation in a given direction. (represents shape of the ground surface as viewed from the side) What is a geologic cross section? -A graphical representation of a vertical slice through the Earth that displays the configuration of rock units and geologic structures underground. What is a digital elevation model (DEM)? -A topographic map produced by a computer from a set of data in which each location is represented by three coordinates: latitude, longitude, and elevation. What is a shaded relief map? -A map that emphasizes the topography of an area by simulating shadows the would be produced by the Sun when located low in the sky HERE BEGINS 12.3 Our planet's surface and near-surface water occupies several distinct reservoirs. Atmospheric water occurs as vapor, as tiny droplets or ice crystals in clouds, and as rain, snow, or hail that falls to Earth's surface. Surface water collects mostly in oceans, but also in lakes, streams, puddles and swamps on land. Frozen water collects in snowfields and glaciers. Below the ground surface, some water dampens soil and rock near the surface, and some sinks deeper and fills underground pores (small open spaces) and cracks as groundwater. -Permafrost exists where soil water and groundwater, extending down to depths of tens to hundreds of meters underground, remains frozen all year. Glaciers and permafrost make up the cryosphere. A significant amount of water also resides in the living organisms of the biosphere. -50 to 65% of the body is water Water constantly flows from reservoir to reservoir, driven by gravity and solar radiation. This never-ending migration is called the hydrologic cycle. -seawater is heated and evaporates into the atmosphere in a gaseous state. -Atmospheric water vapor moves with the wind to higher altitudes, where it cools, undergoes condensation, and precipitates (falls out of the air) as rain or snow. (3/4 of this water goes to the ocean, rest is trapped in land soil or in living organisms, where it will soon return directly to the atmosphere by evapotranspiration (the sum of evaporation from bodies of surface water, evaporation from the ground surface, and release of water by plants and animals)) Rainwater goes back to the sea as surface water or is trapped in glaciers or becomes groundwater. Groundwater flows through the substrate and ultimately returns to the Earth's surface reservoirs. The average length of time that water stays in a particular reservoir during the hydrologic cycle is called the residence time. -Water in different reservoirs has different residence times --ocean 4000 years, lakes and ponds for 10 years, rivers for 2 weeks, atmosphere for 10 days. --Water can stay underground for anywhere from 2 weeks to 10,000 years OR EVEN LONGER. Much of the Earth's surface hosts unstable slopes, meaning that the materials of the slope—including rock, regolith (a general term for soil, unconsolidated sediment, and weathered fragments of rock that lie above coherent bedrock), snow, or ice—might start moving downslope if disturbed. Geologists refer to the gravity-driven tumbling, flowing, or sliding of these materials downslope from higher elevations to lower ones as mass wasting, or mass movement. -first step in transportation of sediment in rock cycle (and most rapid means of modifying slopes). mass wasting is a type of natural hazard -increasingly more of a threat as human population grows and expands its reach Most people refer to any mass-wasting event as a landslide. -Types distinguishable by: --the type of material involved (rock or regolith) --the velocity of movement (slow, intermediate, or fast) --the character of the moving mass (coherent, chaotic, or slurry) --the environment in which the movement takes place (subaerial or submarine) The Hydrologic Cycle figure is in 12.4 The largest water reservoir by far is the ocean, which covers 71% of the Earth's surface.

Chapter 13, Section 13.6 and Box 13.2 (p. 384 - 387 and 391) Notes

During a flood, the volume of water flowing down a stream exceeds the volume of the stream channel, so water overtops the banks and spreads out over a floodplain or delta plain, or fills a canyon to a greater depth than normal. When news reports say that a stream has risen above flood stage, they mean that the water level in the stream lies above the elevation of the stream's floodplain, has overtopped the stream's banks, or has submerged property of value. Floods can be classified in different ways: location-based distinguish among river floods, coastal floods, and urban floods, whereas time-bad classifications distinguish between slow-onset floods and flash floods. A flood that takes days to develop, lasts for days to weeks, and involves the trunk stream of a drainage network can be called a slow-onset flood. -These happen when the ground becomes saturated and cannot absorb any more water, so runoff increases. This often occurs during the spring when snowmelt happens quickly during sustained rains in a wet season, or when a storm system remains stationary over a region for a long time. THEREFORE THEY CAN BE CALLED SEASONAL FLOODS Atmospheric rivers are streams of very moist air that can drop torrential rains over land. An event during which the discharge of a stream increases so fast that it may be difficult to escape from the path of the water is a flash flood. -Floodwaters can subside in minutes to hours and affect small areas. -Happens under periods of intense rainfall (no time for it to sink into the ground, so it becomes runoff) or when dams collapse. -Flash floods can become so turbulent and fast, and carry so much sediment, that they carry away everything in their path. -Flash floods can take place in any climate, but are especially dramatic in arid regions, where a thunderstorm can suddenly trigger a muddy, turbulent flow in a dry wash. Water is said to be crested at a maximum level. Flood control: -Excess dams to store runoffs -Artificial Levees of sand and mud -Floodwalls of concrete (designed to increase the channel's volume and to isolate portions of floodplain flooding) ***These were not fit to handle HUGE floods Undermining occurs when rising water levels increase the water pressure at the base of the river channel, forcing water through sand under the levee. -Levee eventually collapses after water spurts out of the ground Newer flood control approaches involve both restoration of wetland areas along rivers—for wetlands can absorb significant quantities of floodwater—and designation of floodways, regions in which construction has been banned so that floodwaters have room to spread out without causing expensive damage. Area susceptibility to flooding of a given size is done through researchers keeping records of the variation of a stream's discharge, as well as when and by how much a stream rises above flood stage. Such data helps them calculate the average frequency of floods of a given size. HERE BEGINS BOX 13.2 (in 13.7) -Hydrologists characterize the risk of flooding in two ways --The annual probability of flooding indicates the likelihood that a flood of a given size will happen along a specified portion of a stream during any given year. (1% means a 1 in 100 chance it will happen in any given year) --The recurrence interval of a flood with a given discharge indicates the average number of years between successive floods of that side. (100 year flood means one of that size happens once every 100 years) ---Annual probability=1/recurrence interval ---Recurrence interval for a flood with a larger discharge is longer than that for a smaller flood because large floods happen less frequently than small ones. By knowing the discharge for a flood of a specified annual probability, and by knowing the shape of the stream channel and the elevation of the land bordering the stream, geologists can predict the extent of land that will be submerged by a flood of a given size. Such data, in turn, permit geologists to produce flood-hazard maps. (shows areas likely to be flooded) ***A 100-year flood covers a larger area than a 2-year flood and occurs less frequently.

Chapter 13, Sections 13.1 - 13.5 (p. 371 - 384) Notes

HERE BEGINS 13.1 Earth's freshwater can occasionally cause catastrophes. But freshwater-defined as water that contains less than about 500 parts per million (0.05%) dissolved salts-also plays key roles in the Earth System. -an essential component of life on land, and a sculptor/transporter of Earth's materials. --freshwater also provides food, transportation, and power to human society. Freshwater accounts for just 2.5% of the total volume of water in the Earth's surface and near-surface realms. -69% of this resides as ice in glaciers and permafrost -30% of this lies hidden beneath the surface as groundwater -fresh liquid water in lakes and wetlands, streams, soil, air, and organisms-accounts for only about 1% of the total. Surface water is informally referred to as water in lakes, wetlands, and streams. HERE BEGINS 13.2 Streams are flowing bodies of water, but a lake is a standing body of water that occurs on land (does not overlie oceanic crust, and seems to stay in place). -most lakes are freshwater, have inputs and outputs of water so flow occurs slowly, Large lakes have long residence times (years) while small lakes have a residence time of days Lake water level can vary depending on input and output balance. -Permanent vs ephemeral lakes A salt lake becomes salty because it has no outlets, so water can leave the lake only by soaking into the lake bed or by evaporating into the air. Evaporation removes water molecules but leaves behind dissolved ions, so over time, salts become progressively concentrated in the lake water. Many lakes exist simply because they are low areas that receive inputs from streams, rain, meltwater, or spring water. -Some are consequences of geologic phenomena (13.2 for examples) In a wetland, the water is shallow enough that vegetation growing in it rises above the surface. -Different types based on hosted vegetation: --Woody plants grow in a swamp. --grasses grow in a marsh --decaying vegetation and miss fill a bog. Wetlands are important breeding grounds for birds, fish, and insects, and amphibians. HERE BEGINS 13.3 After evaporation, precipitation occurs during the hydrologic cycle, which accumulates on land in surface water (puddles, lakes, wetlands, or snowfields), some sinks into the ground, and some gets absorbed by plants. Gravity causes excess surface water to flow downslope as runoff. -When runoff starts flowing, it does so as a thin film known as sheetwash. -where the land surface is weaker, or flow happens to be a bit faster, the flow digs down into its substrate (the material at and just below the surface) and produces a trough-like depression or channel. A stream is a body of flowing water; streams flowing on land are confined to a channel, except during floods; a large stream is commonly known as a river. -streams receive water from sheetwash, rain and snow, soil, and springs (outlets through which groundwater returns to the surface). On flat ground water accumulates in puddles or swamps, but flows downslope on slopes in streams Over time, continued erosion causes a stream channel to deepen, a process called downcutting, as well as to lengthen at its origin (headwaters), a process known as headward erosion. -With continued downcutting, new side channels, or tributaries form on this land surface and flow into the initial, dominant channel, or trunk stream. --tributaries are smaller streams that flow into larger stream --This process establishes a drainage network, a linked association of channels that remove surface water from a drainage basin or watershed. ---drainage networks can be-dendritic, radial, rectangular, trellis, and parallel-based on the basis of the network's map pattern. (IN FIGURE) A drainage divide separates one drainage basin from another. -The largest are continental divides which separate drainage networks flowing into one ocean from those flowing into another. Which stream carries more water? Must assess a stream's average discharge-the volume of water that passes through a cross section of the stream in a given time. ***calculate by D=A*v (A is cross sectional area of the stream and v is the average velocity at which water moves in the downstream direction) (cubic meters or cubic feet per unit of time) not all water in a stream travels at the same velocity. -Friction slows water flow, so water near the channel walls or near the streambed (the floor of the channel) generally moves more slowly than does water in the middle of the flow. --In detail, turbulence-the twisting, swirling motion of a moving fluid-causes water to follow paths that greatly extend the channel's length. In fact, water may flow upstream in part of an eddy, and within whirlpools it flows in a spiral. A stream's average discharge reflects the size of its drainage basin and the climate where the stream flows. -lots of rain, more discharge (less drainage basin=more discharge?) -Discharge varies with the seasons, as it tends to be greatest when winter snows are melting rapidly, or during a rainy season. -Discharge decreases downstream because water seeps into the streambed or evaporates. Permanent streams flow all year and ephemeral streams flow only part of the year. -When flow in an ephemeral stream vanishes, its channel becomes a dry wash. HERE BEGINS 13.4 How does flow erode the Earth's surface? -Four ways: --Scouring happens when running water picks up and carries away loose sediment. --Breaking and lifting takes place when running water separates and lifts chunks of rock from the channel. --Dissolution separates ions from minerals in the channel wall, and the stream carries these ions away as solutes in solution. --Abrasion happens when sediment-laden water acts like sandpaper and rasps away at the channel. ---In places where turbulence produces long-lived whirlpools, abrasion can carve a bowl-shaped depression, called a pothole, into a streambed. The efficiency of stream erosion (or fluvial erosion meaning river erosion) depends on the discharge of the stream and on the stream's sediment content. -A large volume of fast-moving, turbulent, sandy water causes much more erosion than a trickle of quiet, clear water, so most stream erosion takes place during floods. --The supply of sediment in a stream comes not only from erosion of the stream's channel, but also from landslides that carry debris down slopes bordering the stream and dump it into the stream. A stream's sediment load, meaning the total volume of sediment carried by a stream, includes three components: -Suspended load, consisting of silt- or clay-sized grains that swirl along with the water without settling to the streambed -Bed load, consisting of relatively large clasts that bounce or roll along the streambed -Dissolved load, consisting of ions in solution Stream's ability to carry sediment hinges on Competence and Capacity: -Stream competence refers to the maximum clast size the stream can carry-more competence means can carry larger clasts. This depends on both water velocity and viscosity, so you want a fast-moving, turbulent stream containing. -Stream capacity refers to the total quantity of sediment the stream can carry. This depends on both competence and discharge, so a large fast-moving river has more capacity than a small, slow-moving creek. If the flow velocity of a stream decreases, then the competence of the stream also decreases, and its sediment load starts to settle out. -Sizes of the clasts that settle at a particular location depend on the flow velocity at that location. If the stream only slows a little large clasts settle, if it slows a lot, medium clasts settle (fine clasts settle at a near standstill). Sorted sediments deposited by a stream are called fluvial deposits or alluvium. Coarser alluvium may accumulate along the streambed in elongate mounds known as bars. During floods, a stream may overtop the sides, or banks, of its channel and spread out over its floodplain, a broad, flat area bordering the stream. -Friction slows flow on the floodplain, so fine-grained alluvium settles out to form floodplain deposits. -Where a stream empties into a standing body of water, the slowdown of flow causes a wedge of sediment called a delta to accumulate. The outlet is the mouth of a river. What is a stream gradient? -The slope of a stream's channel in the downstream direction. What is a stream's longitudinal profile? -An idealized longitudinal profile has a concave-up shape, emphasizing that streams have steep gradients near their headwaters and gentle gradients near their mouths. Longitudinal profiles of real streams are not perfectly smooth curves, but rather display local steps. The lowest elevation on a longitudinal profile, meaning the lowest elevation to which a stream can downcut, defines the base level of the stream. -A lake, reservoir, or resistant rock cliff can act as a local base level along a stream-these local base levels are the local steps that appear along a longitudinal profile. A standing body of water at the mouth of a trunk stream serves as the ultimate base level of a drainage network, the lowest level of its longitudinal profile. ***For streams that flow into the ocean, sea level represents the ultimate base level HERE BEGINS 13.5 As streams flow, they both carve into and remove their substrate and leave behind sedimentary deposits, producing a variety of distinctive fluvial landscapes. -Character of these landscapes depends on location along the stream's longitudinal profile, on the nature of the substrate, on vegetation, and on climate. As plateau rose, downcutting by the Colorado River produced the Grand Canyon. -In regions where the land surface lies well above the base level, a stream can carve a trough much deeper than the channel itself. We refer to the trough as a canyon if its walls slope steeply, and as a valley if they slope gently. Whether stream erosion produces a canyon or a valley depends on the rate at which downcutting takes place relative to the rate at which mass wasting causes the walls on either side of the stream to collapse. -canyon develops where stream downcuts faster than the walls collapse -Valleys develop where walls collapse as fast as the stream downcuts. -If a stream cuts through alternating layers of resistant and nonresistant rock, the resulting canyon has a stair-step profile. Rapids are intervals of a stream where the water surface is particularly turbulent and rough. -These develop where water flows over ledges or boulders in a streambed, where the channel abruptly narrows, or where the channel's gradient abruptly changes. --Turbulence in rapids generates eddies and waves that roil and churn the water surface to yield whitewater, a mixture of bubbles and water. A waterfall exists where the stream gradient becomes so steep that the stream's water free-falls above the streambed. -The energy of falling water may excavate a plunge pool at the base of the waterfall. -Waterfalls develop as headward erosion eats away the resistant ledge that underlies them. In places where runoff flows over gently sloping land surface, two distinctive types of streams evolve: braided streams and meandering streams. -Depends on the character and volume of the stream's sediment load and on the cohesion of the stream's banks (meaning the degree to which they can hold together). --A braided stream develops where flowing water carries abundant coarse sediment (sediment source is nearby) and where the stream's banks have low cohesion. ---The adjective braided emphasizes that the stream consists of multiple channels that weave around elongate sediment bars and therefore entwine like hair on a braid. ---A braided stream forms: During floods, water in the stream rises and picks up large volumes of sediment, which it transports downstream. When flooding stops and the water slows, sediment settles out in elongated bars, and the remaining water divides to flow in the low areas between the bars. --A meandering stream develops where sediment doesn't choke the stream and where teh stream's banks have high cohesion either because their materials stick together or because they are bound by plant roots. ---The adjective meandering emphasizes that the stream's channel winds back and forth in a succession of snake-like curves called meanders. ---How do meanders form and evolve: Even if a stream starts out with a straight channel, the location of the strongest current in the stream tends to wander, so that it sometimes lies nearer the center of the channel and sometimes nearer the banks. Water erodes more rapidly where it flows faster, so when the fastest current runs along the bank, the stream digs into the bank, carving into it and producing a small escarpment (a steep slope) called a cut bank. As the process continues, the deepest part of the channel (known as the thalweg) stays put along the outer arc of the curve. Meanwhile, on the inside edge of the curve, water slows down, its competence decreases, and sediment accumulates in a wedge-shaped deposit called a point bar. As time passes, the cut bank moves outward, the point bar grows wider, and the curvature of the meander becomes more pronounced. Soon curvature intensifies and neighboring meanders may approach each other until only a narrow isthmus, known as a meander neck, separates them. When erosion finally eats through a meander neck, a cutoff develops. The meander that has been cut off them becomes a curving oxbow lake. If sediment fills in the lake, the curving depression remains visible as an abandoned meander. Most meander stream channels cover only a relatively small portion of a broad, nearly flat floodplain. What are natural levees? -Ridges that develop on either side of a stream as a result of the accumulation of sediment deposited naturally during flooding. Where a stream exits a narrow canyon onto a plain in a dry environment, this sediment forms a wedge called an alluvial fan, and where a stream enters a standing body of water, such as a lake or the sea, it forms a delta. -Particular shape of a delta depends on the interplay between the rate at which the river supplies new sediment and the rate at which waves or currents remove sediment. --If delta is thick and wide, it forms a broad delta plain. --On alluvial fans and deltas, streams divide into several branches known as distributaries. If the land surface under a drainage network rises or the base level of the network falls, stream rejuvenation takes place, meaning that the streams start to downcut again. Rejuvenation of a meandering stream may produce dramatic incised meanders. If regional uplift causes the tilt of the land to change, the flow of streams in a drainage network may eventually change direction, a phenomenon known as a drainage reversal. The details of fluvial landscape evolution can also be complicated by local uplift or subsidence. If headward erosion causes the channel of one stream to intersect the channel of another, the water of one stream may start to flow down the channel of the other, a phenomenon known as stream piracy.

Chapter 13, Sections 13.7 - 13.10 (p. 387 - 407) Notes

HERE BEGINS 13.7 When it rains, some of the water that falls on the land sinks or percolates down into the ground, a process called infiltration. -Some descends only into the soil. This water, soil moisture, may later evaporate, be absorbed by plant roots, rise back to the ground surface, or seep into streams. --The remainder sinks deeper into sediment or rock, where along with water trapped in rock at the time the rock formed, it makes up groundwater. ---groundwater exists only in Earth's upper crust (depth in 13.7) ----below these depths, metamorphic reactions incorporate water, plastic flow of rock destroys space for water, or water no longer can exist in liquid form. Geologists refer to a small space within a volume of sediment or within a body of rock as a pore, and to the total volume of open space within a solid material, specified as a percentage, as porosity. (30% porosity means 30% of the volume of the block consists of open space) -Porosity includes both pores between solid mineral grains in sediment or rock and cracks of various sizes. For groundwater to flow, pores or cracks in rock or sediment must be linked by conduits (openings). The resulting interconnectivity determines a material's permeability. Groundwater flows easily through a permeable material such as looses gravel, flows slowly through a low-permeability material, and can't flow at all through an impermeable material. Permeability depends on: -Number of conduits: more=more permeable -Conduit size: Fluid travels faster through wider conduits than narrower ones. -Conduit Straightness: Water flows faster through straight conduits than it does through crooked ones. Isolated pores occur in the spaces between grains in a sandstone. Water or air can fill these pores. Fractures provide porosity Permeability is the degree to which pores are linked and water can move from pore to pore in rock or sediment. A high porosity rock or sediment does not necessarily have high permeability-a material whose pores are isolated from one another can have high porosity but low permeability. Geologists distinguish between an aquifer (sediment or rock that transmits water easily), rock or sediment with high permeability and porosity, and an aquitard, rock or sediment with low permeability regardless of porosity. Geologists further distinguish between an unconfined aquifer, which starts at the ground surface and extends downward, and a confined aquifer, which is separated from the ground surface by an aquitard. Not all rock or sediment underground contains water-filled pores, so geologists also distinguish between the unsaturated zone, in which water only partially fills pores so that some air-filled pore space remains, and the saturated zone, in which water completely fills pore spaces. The underground boundary between the unsaturated zone (above) and the saturated zone (below) is called the water table. In effect, the water table forms the top boundary of groundwater. Typically, some groundwater seeps up from the water table due to capillary action caused by the attraction of water molecules to one another and to grain surfaces, producing a wet capillary fringe just above the water table. The depth of the regional water table varies with location -No unsaturated zone when at ground surface and the ground is wet and soggy. -Ground surface is dry when hidden below the ground surface. -In depressions or channels where the ground surface lies below the water table, the low area fills with water and becomes a lake or stream-in such places, the surface of the lake or stream represents the water table. -humid regions it is closer to the surface where arid regions have it further below the surface -Rainfall changes water table depth, so it drops during the dry season and rises during the wet season. --shale is an aquitard which can lie within a thick aquifer. If a mound of groundwater accumulates above an aquitard lens (impermeable), its top surface will lie above the regional water table. Geologists refer to the top surface of such a mound as a perched water table. In hilly regions, the shape of the regional water table tends to mimic the shape of overlying topography. -water table at higher elevation beneath hills In an unsaturated zone, water simply percolates downward, like the water passing through a drip coffee maker, for this water moves only in response to the downward pull of gravity. -Below the water table, groundwater moves not only in response to gravity, but also in response to differences in pressure (can go sideways or upward now). --Pressure comes from the weight of all overlying water from that point up the water table (rock weight does not contribute to the pressure). A point at a greater depth below the water table feels more pressure than does a point at lesser depth. --Both the elevation of a volume of groundwater and the pressure within the water provide potential energy that, if given a chance, drives groundwater flow. ---curved paths eventually take groundwater from regions where the water table is high (such as under a hill) to regions where the water table is low (such as below a valley). A location where water enters the ground, meaning a place where flow has a downward trajectory, is a recharge area, whereas a page394 location where groundwater flows back up to the ground surface is a discharge area. Groundwater moves much more slowly than flowing surface water (long residence time underground). -Groundwater moves so slowly because it follows a crooked network of tiny conduits and must travel a much greater distance than it would if it followed a straight path, and friction between groundwater and conduit walls slows its flow. --The velocity of groundwater flow at a location depends on the slope of the water table and on the permeability of the material through which the groundwater flows. Groundwater moves faster through high-permeability rocks than it does through low-permeability rocks, and it moves faster in regions where the water table has a steep slope than it does in regions where the water table has a gentle slope. Groundwater flows from recharge areas to discharge areas. Typically, the flow follows curving concave-up paths. HERE BEGINS 13.8 Groundwater may be the only source of clean freshwater in arid regions where surface water doesn't exist or in temperate or humid regions where surface water has been polluted. People obtain groundwater from springs and from wells. What is a spring? -A natural outlet from which groundwater spills or seeps onto the ground surface. --Springs form in a variety of geologic settings. Notably, while we can see springs that spill water onto dry land, many springs lie submerged beneath streams or lakes. ***Where groundwater reaches an impermeable barrier, it rises. (spring) ***Groundwater seeps from the ground where a perched water table intersects a slope. (spring) ***A network of interconnected fractures channels water to the surface of a hill (spring) ***Groundwater seeps out of a cliff face at the top of an impermeable sand (spring) ***Where water under pressure lies below an aquitard, a crack may provide a pathway for an artesian spring to form. (spring) What is a well? -A hole that reaches down to the water table. --Two types of well based on the water pressure: ---Ordinary well: Base of the well lies below the water table, so water simply seeps form the aquifer into the well and fills it to the level of the water table. (extraction through pump or bucket) (water level remains the same as long as recharge rate is balanced, water table pumping too fast will sink the water table known as drawdown) ----When drawdown happens, the water table forms a downward-pointing, cone-shaped surface, called a cone of depression, surrounding the well. Drawdown by a deep well may cause nearby shallower wells to dry up. ---Drilling into an aquitard or into rock or sediment in the unsaturated zone, will not provide water, and yields a dry well. An artesian well penetrates a confined aquifer in which pressure pushes water up to a level above the top of the aquifer. -If the level to which the water table would rise lies below the ground surface, the well is a nonflowing artesian well. -But if the level lies above the ground surface, the well is a flowing artesian well (actively fountains out of the ground). ***Artesian wells exist where the recharge area for the confined aquifer lies at a higher elevation than the site of the well, so that if the aquifer were not confined, the water table would be higher. Hot springs, defined as natural springs whose water has a temperature above 30 degrees Celsius (86 degrees Fahrenheit), can be found in two types of geologic settings: -Some occur where groundwater can rise relatively rapidly from several kilometers below the surface, depths at which rock is warmer even with a normal geothermal gradient (rise must be fast to conserve heat, can happen in places where fractures and faults provide a high-permeability pathway) -Hot springs may also develop in geothermal areas, regions of igneous activity where magma-heated rock lies relatively close to the Earth;s surface and warms up water that has infiltrated only a short distance downward. In places where the hot water rises into volcanic ash, a viscous slurry forms and fills bubbling mud pots. -hot springs also associated with heat loving bacteria and archaea, and precipitation of colorful sedimentary rocks What are geysers? -Fountains of steam and hot water that erupt episodically. --form when groundwater seeps into irregular fractures in hot rock. Under the elevated pressure underground, the groundwater can become superheated. Superheated groundwater moves up, decreases in pressure, turns to steam, and resulting expansion pushes some water out of the vent, decreasing pressure further. This new, rapid drop in pressure causes more superheated groundwater to vaporize instantly, forming steam page398 that pushes upward, ejecting all the water above it out of the geyser's vent as an eruption. (THIS IS CYCLIC) HERE BEGINS 13.9 Chambers or caverns are large underground open spaces (often interconnected) Passages are tunnel-shaped or slot-shaped underground openings. -In some locations, chambers host underground lakes, and some passages serve as conduits for underground streams. Most large caves made of limestone bedrock because easily dissolvable in slightly acidic groundwater. -Cave formation primarily takes place just below the water table, in this region groundwater acidity remains high. (groundwater becomes acidic when it infiltrates downward through organic matter in overlying soil. In some cases, acidity results from the interaction of groundwater with sulfur-bearing hydrocarbons) The shape of a cave reflects variations in the composition and in the permeability of the rock from which it formed. -Larger open spaces develop where the limestone is most soluble or where groundwater flow is fastest. --Passages typically follow pre-existing joints, for the joints provide conduits along which groundwater flows more easily. The location of caves are controlled by jointing and bedding in limestone. Passages follow joints, and chambers preferentially form in more soluble beds. When water table drops below the level of a cave, the cave becomes an open space filled with air. -Downward percolating groundwater containing dissolved calcite changes the surface of the cave gradually, for as soon as groundwater enters the air, it releases some of its dissolved CO2 and evaporates a little. As a result, calcite precipitates out of the water, producing travertine. The travertine builds into intricately shaped cave deposits, or speleothems. ***Distinctive landscapes, called karst landscapes, develop at the Earth's surface over limestone bedrock that has undergone dissolution. Where water drips form the ceiling of the cave, the precipitated limestone builds an icicle-like cone called a stalactite. Where the drips hit the floor, the resulting precipitate builds an upward-pointing cone called a stalagmite. -If this process continues long enough, a stalagmite can merge with an overlying stalactite to form a column. In some cases, groundwater flows along the surface of a wall and precipitates to produce drape-like sheets of travertine called flowstone. What is a sinkhole? -A circular depression in the land surface that forms when an underground cavern collapses. --fills with water to form sinkhole lake. What are karst landscapes/karst terrains? -A region underlain by caves formed in limestone bedrock, some of which have collapsed, so that the land surface has sinkholes separated by limestone ridges or spires. --Characterized by sinkholes AND: ---disappearing streams that re-emerge from a cave entrance downstream (surface stream flowing into a crack or hole that link to caves below) ---Natural bridge (leads to tower karst?) ----Karst landscapes evolve over time, and as the water table drops, different levels of caves may form HERE BEGINS 13.10 The sustainability of clean surface-water supplies has come under threat: -Pollution: People dump sewage, garbage, runoff from streets, spilled hydrocarbons, toxic chemicals from industrial sites, fertilizer, and animal waste into streams. These pollutants poison aquatic life and make water unsafe to drink. -Eutrophication: An influx of nutrients-from sewage, fertilizer-rich runoff from fields or lawns, and animal waste-can disrupt freshwater ecosystems. An oversupply of nutrients, or eutrophication, can trigger algal blooms that not only turn water bright green but can also make it toxic. In addition, the decay of dead algae can remove so much oxygen from the water that fish and other organisms living in it die off. -Water Depletion: In many localities, society consumes so much of a stream's water that only a trickle reaches the stream's mouth. In locations where streams supply water to a lake, such water depletion can cause the lake to dry up. -Dam Construction: Dam construction impounds reservoirs. Filling a reservoir may flood upstream towns and forests as well as scenic canyons and rapids. Also, reservoirs trap sediments and nutrients carried by the stream, preventing them from reaching downstream floodplains and deltas that host farmland. -Changes in Infiltration and Sediment Supply: Urbanization transforms fields and forests into parking lots and other concrete/asphalt structures. Such impermeable materials decrease rainfall infiltration and therefore increase runoff, a change that can contribute to flooding. Conversion of forests and fields into farmland increases the amount of sediment in streams because farmland hosts relatively little plant cover and may be barren for much of the year, so sheetwash flowing across farmland carries sediment into streams. Rocks and sediments typically act as natural filters. -BUT, dissolved salts and minerals can make some natural groundwater unusable. --If wells or springs tap into saline groundwater that is older and lies below fresh groundwater, they may yield water that cannot be used for drinking or irrigation. --Groundwater that has passed through limestone or dolomite contains calcium, magnesium, and bicarbonate ions; such hard water causes problems for consumers because carbonate minerals precipitate from it to form scale that clogs pipes (and soap won't lather in it). -Groundwater that has passed through iron-bearing rocks may contain dissolved iron oxide that precipitates to form rust stains. -And arsenic, a highly toxic chemical, can enter groundwater by the dissolution of arsenic-bearing minerals. In recent decades, increasing amounts of contaminants have been introduced into aquifers by human activities. The underground cloud of contaminated groundwater that flows away from a contaminant source constitutes a contaminant plume. -Sometimes, natural processes can clean up groundwater contamination (clay, oxygen, and natural bacteria do the cleaning job) -Wells in the path of contaminant plume can be shut down to prevent further contaminations. -If resources permit, the groundwater can be extracted and purified. --Also, engineers can instal an underground wall of chemicals that causes the contaminants to precipitate as solids so that they can not migrate with groundwater, or they may inject oxygen and nutrients into the plume to foster growth of bacteria that can react with and break down the contaminants. Groundwater is renewable in a time frame of 10,000 years. -By pumping water out of the ground at a rate faster than nature replaces it, people are "mining" groundwater reserves --Lowering the water table: We outflow>inflow, water table can drop and springs, streams, lakes, swamps, and nearby wells dry up. --Reversal of groundwater flow direction: The cone of depression around a well creates a local slope in the water table large enough to reverse the flow direction of nearby groundwater. This change may cause contaminant plumes to head toward wells that were once clean. --Saltwater Intrusion: In coastal areas, fresh groundwater lies in a layer above denser saltwater that has entered from adjacent ocean aquifer. Pumping too quickly can suck this saltwater up into the well. (can happen inland too if lowering of water table requires deeper drilling to saltier groundwater) --Pore Collapse and Land Subsidence: Water can't be compressed, so pore water holds sediment grains apart in the subsurface. Air, however, can be compressed, so removal of groundwater allows grains around pores to pack together more closely. Pore collapse decreases the porosity and permeability of an aquifer. It also decreases the volume of the aquifer, causing land above the aquifer to undergo subsidence (fissuring of ground surface in most cases).

Chapter 15, Sections 15.1 - 15.3 and 15.5 (p. 453 - 461 and 472 - 475) NOTES

HERE BEGINS 15.1 What is the global ocean? -A large body of saltwater between continents -a layer of saltwater with an average depth of 4-5 km (2.5-3 mi) that covers about 70.8% of our planet's surface. This layer contains 1.3 billion km^3 (300 million mi^3) of water. -divided into several geographic regions with different names The Earth's ocean is a dynamic environment in constant motion. Its waters flow over vast distances in currents (stream-like flows), and its surface elevation changes due to both global-scale tides (the daily rise and fall caused by gravitational attraction of the Moon, Sun, and other forces) and the development of waves (local surface undulations). -Ocean water is non-homogenous, for characteristics such as salt content and temperature vary regionally and with depth. HERE BEGINS 15.2 Sailing between islands began as early as 3000 B.C.E. -End of the Middle Ages saw the beginnings of modern ocean exploration. Christopher Columbus's journey across the Atlantic, in 1492, followed by the discovery of sea routes to China in 1498, opened the European Age of Discovery. -25 years later a vessel traveled around the globe -Each voyage brought information about what the edges, or shorelines (boundary between the water and the land) looked like. Latitude represents the distance north or south of the equator, it is calculated by measuring the angle of the Sun above the horizon at noon. Longitude is the distance east or west, became possible to measure in the mid-18th century with invention of mechanical clock. The early explorers who ventured across the sea undertook their voyages primarily in search of gold and spices. The modern science of oceanography (The study of the water and life in the oceans, as well as the way in which ocean water moves and interacts with land and air.), the study of the sea, did not begin until 1872, when Britain's HMS Challenger begin a 4-year cruise that collected enough new information about ocean water and the seafloor to fill 50 books. By using research ships, submersibles, and satellites, modern oceanographers (who study the physical and chemical characteristics and movement of ocean water), along with marine geologists (who study the seafloor and coasts) and marine biologists (who study marine life), continue to enhance our knowledge of our planet's amazing seas. Geographers divide the global ocean into five separate bodies-the Atlantic, Pacific, Indian, Arctic, and Southern Oceans-outlined by continents. -equator divides the Atlantic and Pacific into northern and southern portions. -In addition, geographers recognize several seas (such as the Mediterranean, Black, Red, and Caribbean Seas), bays (such as Hudson Bay), and gulfs (such as the Gulf of Mexico), which are smaller regions of seawater that are partially surrounded by land. -Plate motions have caused and will continue to cause changes in shape of oceans and seas. Sea level refers to the elevation of the boundary between ocean water and the air above. When we use the term sea level, we are actually talking about mean sea level, the average height of this boundary over the course of a year. -At any given moment, the sea surface at a given locality may be higher or lower than mean sea level because of passing waves or the rise or fall of tides. the overall volume of surface water on the Earth has stayed roughly constant relative sea level, the position of sea level with respect to the land surface, does vary significantly over geologic time. DUE TO: -when water gets trapped in large glaciers on land during an ice age, sea level falls relative to land everywhere, whereas when large glaciers melt at the end of an ice age, sea level rises. -When a region of land undergoes uplift, sea level falls relative to the region, whereas when the region undergoes subsidence sea level rises -When the volume of the ocean basins decreases (by increasing the volume of mid-ocean ridges or by building oceanic plateaus) sea levels rise globally, whereas when the volume of ocean basins increases, sea level falls. When relative sea level rises significantly, ocean water may submerge large areas of continents to form epicontinental seas, and when sea level falls, portions of continental shelves, the relatively shallow part of the ocean adjacent to continents, may be exposed. ***Mean sea level is the average elevation of the sea surface over the course of a year. It is halfway between average high and average low tide at a particular location. ***Sea-Level change over geologic time chart in figure (15.2) -Era's and how things changed Researchers suggest that this recent rise primarily reflects an increase in seawater temperature, for liquid water expands when heated, but it also reflects the continued melting of glaciers. SEA LEVELS HAVE RECENTLY ROSE CONSIDERABLY HERE BEGINS 15.3 Oceans formed when the planet cooled enough for water vapor to condense and fall as liquid water that could collect in ocean basins. -How water formed in (15.3) Individual molecules of water can remain in the ocean for 4,000 years before turning to water vapor in the air. Then, within hours to days, the vapor condenses or crystallizes and falls back to Earth's surface. Salty taste and easier floating than in freshwater is because ocean water is a solution containing dissolved salts. In a solution, dissolved ions fit between water molecules without changing the overall volume of the water, so adding salt to water increases the water's density. You float higher in a denser liquid (seawater) than in a less dense liquid (freshwater) because, according to Archimedes' principle, an object sinks in water only to a depth at which the weight of the water displaced equals the weight of the object. Typical seawater contains 96.5% water and 3.5% salt by weight. Salinity is the concentration of salt in water. -Depends on: --Water temperature (warm water can hold more salt in solution) --Balance between inputs of freshwater and removal of freshwater by evaporation. ***For example, in estuaries (created when a coastal valley is flooded because of either rising sea level or land subsidence), places where seawater floods the mouth of a river, salty seawater mixes with fresh river water to produce brackish water that has less salinity than seawater (brackish water also develops where glacial meltwater enters the sea or where heavy rain falls on the sea surface). ***Along the margins of restricted seas in hot, arid climates, so much water evaporates that the remaining water becomes brine, meaning that its salinity becomes greater than that of seawater. --Ocean salinity also varies with depth, as the largest variation is in the upper 1 km of the sea because it is most affected by evaporation or freshwater inputs. Salinity in deeper water tends to be more homogenous. Oceanographers refer to the gravitational boundary between surface-water salinities and deep-water salinities as the halocline. Sea salt consists of: -Sodium -Potassium -Calcium -Magnesium -Chloride -Sulfate ***most ions are sodium and chloride (85%), known as halite mineral... other mineral names in 15.3 ***Salt (halite, NaCl) can precipitate directly in brines. Most dissolved ions in the sea are produced by the chemical weathering of rock and are carried to the sea by flowing groundwater and river water. (HOW OCEANS GET SALT) -Carbonate gets extracted by organisms making shells, whereas salt concentrations are high due to not being extracted The correlation of average annual sea-surface temperature with latitude exists because the total amount of solar radiation reaching the Earth's surface varies with latitude. The amount of solar radiation also varies with the seasons, so sea-surface temperature varies with the seasons as well, but not by as much as air temperature does, because water has a high heat capacity, meaning that it can absorb or release large amounts of heat without changing its temperature very much. Water temperature in the ocean varies markedly with depth in tropical and temperate latitudes, for water heated by the Sun expands and becomes less dense than colder water. Therefore, warmer water "floats" above denser, colder water; the boundary between warmer water above and colder water below defines the thermocline. -pronounced thermocline doesn't develop in polar sea due to surface waters already being so cold, so no temperature contrast. Both temperature and salinity control the density of seawater, so ocean-water density varies laterally and vertically. -Water density of seawater is 2 to 3% more dense than freshwater. (densest water is at the seafloor, is densest due to overlying water weight, low temperature, high salinity) What is pycnocline? -A boundary between layers of water of different densities in an ocean or lake. --A less dense shallow layer extends down from the surface to the pycnocline, and a denser deep layer continues from the pycnocline down to the seafloor. Sea water can be made drinkable! Salt can be removed from water by desalination. -Distillation: workers pump seawater into a tank and heat the water to accelerate evaporation. When seawater evaporates, it leaves its salt behind, so the resulting vapor consists of freshwater-and condensation of the vapor produces liquid freshwater. Most commercial distillation operations use multi-stage flash distillation (low pressure, water boils at lower temperatures). -Reverse osmosis purifies seawater without heating it. During this process, workers apply pressure to push water through a semipermeable membrane that allows water molecules, but not salt molecules, to pass through it. (goes from high conc to low conc, where normal osmosis goes from low conc into high conc, SO REVERSE) ***Both distillation and reverse osmosis take energy. NEED TO USE MORE ENERGY AND DISPOSE OF HARMFUL BRINE IF DOING DESALINATION What is a water mass? -In the context of oceanography, a large volume of water in the ocean with relatively uniform density characteristics, due to its relatively uniform temperature and/or salinity. ***Due to variations in density, the oceans are stratified into distinct water masses. Seawater density varies with depth and changes most rapidly over an interval called the pycnocline. The depth and thickness of the pycnocline vary with latitude. HERE BEGINS 15.5 Waves-the periodic up-and-down motions of the ocean at a scale that generates distinct troughs and ridges visible to your eye-make the ocean surface a restless, ever-changing vista. -The waves you see when you look out at the sea from the shore, a plane window, or a ship's deck are wind-driven waves. These waves form due to the interaction between moving air and the surface of the ocean. -Tsunamis, a type of wave caused by sudden displacement of water due to slip on a fault or a landslide, are relatively rare.) Wind driven waves begin by: -The horizontal surface of the water represents an equilibrium level-if you pushed the surface up or down with a paddle, it would return to that level because of gravity. At the surface, water molecules attract one another more strongly than they attract air molecules above. This attraction produces surface tension, which makes the water surface behave somewhat like an elastic sheet. When a breeze starts to blow, frictional drag causes this elastic surface to stretch. As soon as it stretches, elastic rebound causes it to twang back like a rubber band, and as a consequence, it wrinkles into small waves called ripples. Once ripples exist, wind can push against hteir sides, causing them to build still higher. A ripple can evolve into a wave that lifts water well above the equilibrium level. When this happens, gravity acts on the elevated water in the wave, causing it to sink. Inertia causes the sinking water surface to descend below the equilibrium level. Next, the water surface bounces back up and rises above the equilibrium level, and the process repeats, like the up-and-down motion of a weight suspended from a vertical spring. (wave train) -Ripples are a very small wave formed by the frictional drag of the wind on the surface of a water body. (elastic behavior of the ocean surface) -A wave train propagates outward, across the water surface, and can move a long distance from the location of the disturbance. The top of a wave is its crest and the base is its trough. The vertical distance between the crest and the trough is the wave height, and half the wave heigh represents the wave's amplitude. The horizontal distance between two successive troughs or two successive crests defines the wavelength. The number of wave crests (or troughs) that pass a point in a given time defines the wave frequency, and the time between the passage of two successive crests (or troughs) is the wave period. The horizontal velocity at which a crest or trough moves gives the wave speed. A particle of water within an ideal wave moves in a circle, with the greatest diameter at the ocean's surface. -a depth equal to half the wavelength is the wave base-no movement takes place at all here. Wave drift, an overall lateral motion accompanying the passage of a wave, occurs where waves develop due to the frictional drag of the wind. ***1/4 of wave length usually ***Wave drift causes surface currents!!!! Size of waves generated by wind in the open ocean depends on the strength of the wind (how fast the air moves), on the fetch of the wind (the distance over which it blows), and on the length of time during which the wind blows. ***during strong winds, not all energy goes into making waves, water can mix with air and make whitecaps when tops of waves are blown over. ***amplitudes of 6-30 ft and wavelengths of 130-1,600 ft. Waves always move more slowly than the wind that generates them, but wave speed depends on wind speed. -faster wind causes faster waves (6-30 mph wave speeds are possible) the speed of waves depends on their wavelength: waves with longer wavelengths travel faster. Wave dispersion occurs because wave trains travel outward from their source at different speeds and separate far from the source. ***different wavelengths is a chaotic sea (far from the source has regularly spaced waves so calmer) Waves that have traveled away from their source, and are not being driven by the local wind are called swells. Large waves may form by constructive interference, which takes place when two wind-driven waves moving from different directions come together in such a way that wave crests overlap to form a single, higher elevated crest. -Occasionally, these processes lead to the formation of a rogue wave, defined as an isolated wave that rises more than twice as high as most large waves passing a locality during a specified time interval.

Chapter 16 (all) (p. 487 -521) NOTES

HERE BEGINS 16.1 Human-piloted submersibles are one of many tools employed to collect data about the 70.8% of the Earth's solid surface that lies hidden beneath seawater. Orbital satellites can characterize regional-scale bathymetry (the shape of the seafloor) in general, and shipborne sonar can define local-scale bathymetry in detail. Shipborne tools can also yield seismic-reflection profiles, cross-sectional images that reveal the configuration of layering under the seafloor. By dredging (pulling a chain net along the seafloor) and by coring (plunging hollow tubes into the seafloor), researchers can collect samples of seafloor rocks and sediment. -And by using drilling ships that are capable of boring holes, researchers have recovered oceanic crust from depths of up to 4 km (2.5 mi) below the seafloor. --Geologists may use the same tools to study the coast (the shore and the adjacent areas of land and sea). But on coasts, they can also make direct field observations. Reseults of research in this facet can provide the knowledge base of marine geology, the study of the ocean's floor and margins. -study of the seafloor and oceanic crusts Seismic-reflection profiling helps characterize the layering of sediments and rocks beneath the seafloor. HERE BEGINS 16.2 Water would cover earth uniformly at a depth of 2.5 km (1.5 mi) if Earth's crust was all at the same elevation everywhere. Earth's crust consists of higher areas (the continents), and lower areas (the ocean basins) that differ in elevation by an average of 4.5 km (2.8 mi). Due to gravity, water flows downslope, so it drains from continents into the ocean basins to fill the oceans, leaving the surface of continents as dry land. Continental crust is thicker (but less dense) and has different composition than oceanic crust (less thick, more dense). Because of these differences, the surface of oceanic lithosphere sits deeper than the surface of the continental lithosphere—the low areas, underlain by oceanic lithosphere, are the ocean basins. The plastic asthenosphere flows out of the way to let the different types of lithosphere attain their equilibrium positions. The ocean flow can be divided into bathymetric provinces, distinguished from one another by their water depth. What is a continental shelf? -A broad region of shallow sea at a continental margin. The widest continental shelves occur over passive continental margins. -The continental shelf terminates at the continental slope, a surface that descends at an angle of about 2 degrees from a depth of 200m to nearly 4km. From about 4km down to about 4.5 km, the slope angle decreases defining a region called the continental rise. At a depth of 4.5 km, you find yourself above. a vast, nearly horizontal surface known as the abyssal plain. -Passive margins are not plate boundaries and lack seismicity. Passive margins originate after rifting succeeds in breaking a continent in two, so that a new mid-ocean ridge forms and seafloor spreading begins. What is a passive-margin basin? -A region along a tectonically inactive continental margin that had been stretched during rifting, continued to subside due to cooling after rifting ceased, and has filled with a very thick accumulation of sediment. ***Flat surface of this sediment layer constitutes the continental shelf. Active continental margins are seismically active. -sharp descent, continental slope is the face of an accretionary prism, a wedge of sediment that has been scraped off the seafloor. Large submarine slumps may carry immense volumes of debris down continental slopes, and these movements may generate tsunamis. Submarine avalanches known as turbidity currents send abrasive clouds of suspended sediment rushing down continental slopes. These can carve deep underwater valleys, known as submarine canyons (canyon cute into a continental shelf and slope). When a turbidity current reaches the mouth of a submarine canyon, at the base of the continental slope, its flow velocity decreases, so the sediments it carries settle out to produce turbidites made up of graded beds. Layer upon layer of turbidites accumulate and build out a submarine fan, a wedge of sediment that spreads out over the abyssal plain (along passive margins) or the trench floor (along marine convergent boundaries). These fans underlie the continental rise. All 4 plate boundaries can be seen by studying the bathymetry of the seafloor. -Seafloor spreading at a divergent boundary yields a mid-ocean ridge (a submarine mountain belt that rises as much as 2 km above the depth of the abyssal plain). -Oceanic transform faults, strike-slip faults along which one plate shears sideways past another, typically link segments of mid-ocean ridges. Transform faults are delineated by fracture zones, narrow belts of steep escarpments and broken-up rock. -Subduction at convergent boundaries yields a deep-sea trench, a deep, elongate trough bordering a volcanic arc. --Some trenches border continents, lying seaward of an active continental volcanic arc, as is the case along the western coast of South America. Others border island arcs, curving chains of active volcanic islands such as Alaska's Aleutian Islands. As oceanic crust moves away from the axis of a mid-ocean ridge and gets progressively older, it cools and thickensm and as it does so, its surface sinks and its slope decreases (forms abyssal plain). A blanket of pelagic sediment gradually accumulates and covers the basalt of the oceanic crust (consists of plankton shells and volcanic ash or windblown dust that is a form of clay), which fall like snow from the ocean water and settle on the seafloor. The older the seafloor, the longer the time during which pelagic sediment has been accumulating, so over older oceanic lithosphere of the abyssal plain, it becomes thick enough to bury irregularities in the basaltic crust of the seafloor. Oceanic Islands (whose peaks protrude above sea level) and seamounts (whose peaks are submerged) rise above abyssal plains or mid-ocean ridges. Oceanic islands or seamounts that currently lie over hot spots are active volcanoes, whereas those that have moved off the hot spot are extinct. ***some oceanic islands become seamounts by sinking below the water surface. Oceanic islands and seamounts align in a chain parallel to the motion of the oceanic plate over the hot spot- these chains, called hot-spot tracks, define the direction of plate motion. Where hot-spot igneous activity becomes particularly voluminous, a broad oceanic plateau, composed of a layer of basalt up to 3 km (2 mi) thick, develops. Oceanic plateaus represent submarine large igneous provinces. ***In some cases, the top of a seamount may be beveled flat by erosion as its summit reaches sea level. Or the island may be overgrown by a coral reef as it sinks. When such islands sink below sea level, the become flat-topped seamounts, known as guyots. HERE BEGINS 16.3 What is the tide? -the generally twice-daily rise and fall of sea level. ***At low tide, when sea level sinks to its lowest elevation, boats might run aground, whereas at high tide, when sea level rises to its highest elevation, they can make it to open water easily. What is Tidal Range? -The difference between sea level at high tide and at low tide. It varies greatly with location. Tides affect the coast because during a rising tide, or flood tide, the shoreline (the boundary between water and land) moves inland, and during a falling tide, or ebb tide, the shoreline moves seaward. What is the Intertidal Zone? -The surface of the seafloor that lies between the shoreline at high tide and the shoreline at low tide. ***width of the intertidal zone depends on both the tidal range and the slope of the seafloor surface. ******when the tidal range is large and the slope is gentle, the position of the shoreline can move by kilometers during a tidal cycle, so at low tide, the intertidal zone becomes a broad tidal flat exposed to the air. Arrival of a flood tide in the mouth of an estuary, where the tide moves against a river current, can produce a tidal bore, a visible wall of water, ranging from a few centimeters to a few meters high. ***moves at speeds up to 22 mph Tides take place because the water of the ocean moves in response to two forces: -The gravitational attraction of the moon and the Sun -The centrifugal force caused by the revolution of the Earth-Moon system. ***Oceanographers refer to the combination of these forces as the tide-generating force. ***creates two tidal bulges in the global ocean ******One bulge, the sublunar bulge, lies on the side of the Earth that is closer to the Moon, because the Moon's gravitational attraction (the strongest contributor to tides) is greatest at this point. ******The other bulge, the secondary bulge, lies on the opposite side of the Earth, pushed outward by the centrifugal force. *********A depression in the global ocean surface separates the two bulges. When a coastal location passes under a tidal bulge as the Earth spins, it experiences a high tide, and when it passes under a depression, it experiences a low tide. Tides are higher underneath the sublunar bulge than underneath the secondary bulge. Gravitational pull is the attractive force that one mass exerts on another. Centrifugal force, a manifestation of inertia, is the apparent outward-directed (center-fleeing) force that a body on or in an object feels when the object spins or moves in orbit around a point. The Earth-Moon system refers to our planet and the Moon, viewed as gravitationally linked pair as they move together through space. The center of mass is the point within a group of objects, about which mass is evenly distributed. In regard to centrifugal force, it's actually the center of mass of the Earth-Moon system that follows this orbit. -represent the direction and magnitude of centrifugal force with an arrow, or vector, whose length represents the size of the force and whose orientation indicates the direction of the force. Vectors representing centrifugal force do not have the same length and do not point in the same direction as the vectors representing gravitational attraction. -This sum of the gravitational vector and the centrifugal force vector at a point on the Earth's surface is the tide-generating force. The magnitude and direction of the tide-generating force vary with location on the Earth. ***largest vector changes depending on which side of the Earth is closest to the moon or furthest away What factors affect the timing and magnitude of tides? -Tilt of the Earth's axis -The Moon's Orbit -The Sun's gravity: Sun on same side of the earth as the moon or on the side opposite the moon, we experience particularly high flood tides called spring tides. (Sun's gravitational attraction adds to the Moon's)... When Sun and Moon are 90 degrees apart relative to the Earth, lower flood tides called neap tides are experiencing due to these two gravitational forces counteracting. -Ocean-basin Shape: Shape influences the sloshing of water back and forth and can either add or subtract to the tidal bulge. -Focusing effect of bays: Shape of the shoreline influences the tidal range. More narrow leads to a higher tide. At any given location, the tides are periodic and can be predicted. -Used to tell time ages ago. Tides likely larger in the early ocean due to Moon being closer to Earth. Also causes days to grow longer. Also, distance to the Moon increases every year. HERE BEGINS 16.4 The shape of a coast depends on many factors, but first and foremost, it reflects deposition or erosion by waves. In the open ocean, the wave base, the lowest level at which water moves in a wave, for wind-driven waves, lie far above the seafloor, so wave motion has no effect on the ocean floor. In the shoaling zone, nearer shore, however, the wave base touches the ocean floor (causing back and forth motion in sediment) (friction makes circular motion of particles more elliptical closer to shore). Eventually, water at the top of the wave curves over its base, and the wave becomes a breaker, ready for surfers to ride. Breakers crash onto the shore in the surf zone, sending a surge of water up the beach. This upward surge, or swash, continues until friction and gravity bring water motion to a halt. Then gravity draws the water back down the beach as backwash. As a wave approaches shore, friction slows its base. Water motion in the wave becomes more elliptical. The crests of waves that make an angle to the shoreline bend as they approach shore, a phenomenon called wave refraction (angle decreases to less than 5 degrees). -Longshore current: A flow of water parallel to the shore just off a coast that develops when waves move toward the shore obliquely. As backwash moves back to sea, it may concentrate into a strong seaward flow, called a rip current that moves perpendicular to the shoreline. The tidal range varies with the phases of the Moon. Note how the tidal range during neap tide is less than that at spring tides, and that tides are particularly high when the Moon is new. Oceanic islands, seamounts, and plateaus build above hot spots. Coastal landscapes reflect variations in sediment supply, tides, relative sea-level rise or fall, and climate. -Where the supply of sediment is low and the landscape is rising relative to sea level, rocky shores with dramatic cliffs and sea stacks may evolve. Where sediment is abundant, sandy beaches and bars develop. LANDSCAPES AND TECTONICS (16.4) IN SECTION AND FIGURE What is a beach? -A band of sediment, parallel to the shoreline, that undergoes sorting and shifting by the swash and backwash of waves. -waves winnow out finer sediment such as silt and mud and carry it to quieter water offshore. --cobble or "shingle" beaches may persist only where nearby cliffs or debris-choked streams supply large rock fragments. The composition of sand itself varies from beach to beach because different sands come from different sources. Sands derived from the weathering and erosion of felsic to intermediate rocks consist mainly of quartz, a durable material. The other minerals in such rocks weather chemically to form clay, which washes away in the waves. Beaches made from the erosion of limestone, coral reefs, or shells consist of carbonate sand. And beaches derived from the erosion of basalt boast black sand, made of tiny basalt grains. Beaches consists of distinct zones, as illustrated by a beach profile, the variation in elevation of a beach, as measured along a line perpendicular to the shoreline. -Starting from the sea and moving landward: --Foreshore zone includes the intertidal zone across which the tide rises and falls, as well as the beach face, a steeper, concave-up area that forms where the swash of the waves actively scours the sand. --The backshore zone extends from a small step, cut by high-tide swash, to the far edge of the beach farther inshore. The backshore zone includes one or more berms, horizontal to slightly landward-sloping terraces made up of sediment deposited during storms. The sand on the beach, if exposed to persistent winds, may build into sand dunes, similar to those of deserts, along the landward edge of the beach. The inshore edges of some beaches, however, border cliffs or vegetated land not affected by waves. Beach sand doesn't sit still, for typical wave action moves an active sand layer back and forth (the inactive sand layer below moves only during severe storms or not at all.) The width of a beach ultimately reflects the width of the area subjected to frequent wave action. -beach profiles may vary seasonally depending on the types of storms in the area during different seasons. --For example, in mid-latitudes, winter storms tend to be stronger and more frequent than summer ones. The larger, shorter-wavelength waves of winter storms wash beach sand into deeper water, making the beach narrower. But smaller summer waves with longer wavelengths bring sand in from offshore and deposit it on the beach. ***In winter, strong storms move sand offshore. In summer, gentler waves carry sand back to the beach. What is Longshore Drift (or beach drift)? -The net transport of sediment laterally along a beach that occurs when waves wash up a beach obliquely. ***sawtooth pattern, swash moves perpendicular to wave crest but backwash is completely parallel due to gravity. When the coastline indents landward, longshore drift can stretch a beach out into open water and produce a sand spit. -A sand spit is a ridge of sand, parallel to the shore, that stretches out into open water, typically across part of the mouth of a lagoon or bay. --Some sand spits grow across the opening of a bay or estuary to form a baymouth bar. --In regions where the coast has a very gentle slope and there is an abundant supply of sediment, a narrow ridge of sand, known as an offshore bar if submerged, or a barrier island if its crest lies above sea level, lies offshore. Barrier islands, which are parallel to the shoreline may form when ancient beach dunes become partially submerged by another rising sea level. Or they may form where waves break offshore, lose energy, and deposit some of their sediment load. Some barrier islands are simply very long sand spits that built out into a region of shallow sea offshore. The water between a barrier island and the mainland becomes a quiet-water lagoon, a body of shallow seawater separated from the open ocean. Reasons that Outer Banks is a temporary local over the space of geologic time is in 16.4 Tidal flats are broad, nearly horizontal areas of mud and silt that are exposed, or nearly exposed, at low tide but submerged at high tide, develop in regions protected from strong wave action. -Typically found along the margins of lagoons or on shores protected by barrier islands, where, in relatively quiet water, mud and silt can accumulate in thick, sticky layers. --provide a home for burrowing organisms such as clams and worms, so bioturbation (which means stirring by life) constantly mixes tidal-flat sediments and disrupts bedding. The sediment budget-the balance between sediment supplied and sediment removed-plays an important role in determining the long-term evolution of a coastal area. -Sand can be brought by local rivers, offshore by waves, or far away by longshore drift -Sand can be removed by longshore drift, be carried offshore by backwash or rip currents, or be blown inland by wind. ***If new sand does not replace the removed sand, the beach segment grows narrower. If, however, the supply of sand exceeds the amount that washes away, the beach becomes wider. What is a rocky coast? -An area of coast where bedrock rises directly from the sea and beaches are absent. --feels full impact of breakers where rocks can be picked up and break each other due to lack of protection from a beach. Also, because of its turbulence, the water hitting a cliff face carries suspended sand that can abrade the cliff. The combined effects of shattering, wedging, and abrading, together called wave erosion, can gradually undercut a cliff face by making a wave-cut notch. -continues until rock breaks away into a pile of rubble, then water takes rubble inland over time --such cliff retreat leaves behind a wave-cut platform, or wave-cut bench, that becomes visible at low tide. ---Wave-cut platform: A shelf of rock, cut by wave erosion, at the low-tide line that was left behind a retreating cliff. ----salt wedging also can break up rocks along coasts...produces a pattern known as honeycomb weathering. ----Biological processes of animals and plants boring into rocks also gradually breaks rocks Many rocky coasts start out with an irregular coastline, with headlands protruding into the sea and embayments (where shoreline curves inland) set back from the sea. These are often temporary features in geologic time. -Pattern of wave erosion removes debris at headlands and sediment accumulates in embayments, so over time, the shoreline becomes less irregular. A headland erodes in stages: -Because of refraction, waves curve and attack the sides of a headland, slowly eating through it to create a sea arch connected to the mainland by a narrow bridge. -Eventually the arch collapses, leaving isolated sea stacks (A chimney-shaped column of rock produced by wave erosion along a rocky coast) just off shore. Once formed, a sea stack protects the adjacent shore from waves. Therefore, sand collects in the lee of the stack, slowly building a tombolo, a narrow ridge of sand that links the sea stack to the mainland. Sea stacks eventually crumble and disappear. Along some coasts, a relative rise in sea level causes the sea to flood river valleys that merge with the coast, resulting in estuaries, where seawater and river water interact. -Estuaries can develop where, when sea level was lower, a river cut a valley below present sea level, or where the region containing the river valley is slowly subsiding (sinking). ***dendrite patterning on map, bordered by marshes that flood at high tide Seawater and river water may interact in two different ways within an estuary: -In quiet estuaries that are protected from wave action or river turbulence, the water the page513 water becomes stratified, and the denser seawater flows upstream as a wedge beneath the less dense freshwater during flood tide. Such a saltwater wedge migrates... -In turbulent estuaries, such as the Chesapeake Bay, seawater and river water mix to produce nutrient-rich brackish water with a salinity between those of oceans rivers. Estuaries typically host complex ecosystems inhabited by unique species of shrimp, clams, oysters, worms, and fish that can tolerate large changes in salinity. Coastal fjords form where sea-level rise drowns glacially carved valleys. When the water stored in the glaciers returned to the sea and caused sea level to rise, it flooded glacial valleys to produce coastal fjords, narrow fingers of the sea surrounded by hills or mountains. HERE BEGINS 16.5 Along many coasts, however, living organisms control the landforms of shore and nearshore regions. Such organic coasts include coastal wetlands, where salt-resistant plants thrive, and coral reefs, where tiny marine animals build mounds of biochemical limestone. The nature of an organic coast depends on the types of organisms that live there, which in turn depends on climate. The coastal wetland is the gentlest type of nearshore environment. A coastal wetland is a vegetated, flat-lying stretch of coast that floods at high tide, become partially exposed at low tide, and does not feel the impact of strong waves. -wetlands account for 10 to 30% of all marine organic productivity! In mid-latitude climates, coastal wetlands include swamps (wetland dominated by trees), marshes (wetlands dominated by grasses), and bogs (wetlands dominated by mosses and shrubs). In tropical or subtropical climates (between 30 degrees N or 30 degrees S), mangrove swamps thrive along the shore. These are trees that have evolved roots that can filter salt out of water, so they can survive in salt and freshwater. Dense stands of mangroves absorb the impact of waves and, by doing so, prevent coastal erosion. Sea anemones, sponges, clams, and many other organisms grow on or around the coral in coral reefs. The coral is actually a colony of tiny invertebrates related to jellyfish. Coral obtain some of their nutrition by filtering nutrients from seawater; the remainder comes from algae that live within the corals' tissues. Corals have a symbiotic (mutually beneficial) relationship with these algae, in that the photosynthetic algae provide nutrients and oxygen to the corals while the corals provide carbon dioxide and other nutrients to the algae. Coral polyps secrete calcite shells, which gradually build into a mound of solid limestone. -only the surface of the mound is alive (interior is shells from previous generations of coral) What is a coral reef? -A realm of shallow water underlain by a mound of coral and coral debris and associated organisms. --living corals must remain submerged, they absorb wave energy and thus serve as a living buffer that protects coasts from erosion. Corals need clear, warm water with normal ocean salinity, so coral reefs grow only along unpolluted coasts at latitudes below 30 degrees. There are three different shapes of coral reefs: -A fringing reef forms directly along the coast -A barrier reef lies offshore (separated from the coast by a lagoon) -An atoll forms a circular ring surrounding a lagoon. coral reefs associated with oceanic islands in the Pacific start out as fringing reefs, then later become barrier reefs and, finally, atolls. Eventually, the reef itself sinks too far below sea level to remain alive and becomes the cap of a guyot. HERE BEGINS 16.6 Changes to relative sea level, meaning the position of sea level relative to the land surface a at a given location, can result either form global sea-level changes (the rise or fall of sea level worldwide) or from local vertical movement (uplift or subsidence) of coastal land areas, which can take place even when global sea level remains fixed. -Vertical movement of the land may be a consequence of plate interactions, as happens where subduction causes compression and thickening in the crust of the overriding plate at a convergent boundary. -Vertical movement may also reflect the addition or removal of a load (such as glacier) on the crust's surface or the cooling and/or heating of lithosphere (which changes lithospheric thickness and density). -In some cases, local changes in sea level may result from human activity, as happens when people pump out so much groundwater that pores between grains in the underground sediment collapse and the land surface sinks (subsidence). Geologists refer to a coastal location where the land is rising relative to sea level as an emergent coast. -Terraces form where a wave-cut platform has time to develop before uplift brings the platform above the high-tide level. Coasts where the land is sinking relative to sea level are known as submergent coasts. -Estuaries and fjords, landforms that develop when the sea floods coastal valleys, characterize some submergent coasts. -Submergence of coastal plains, nearshore landscapes of low relief, may produce broad wetlands and lagoons. The quantity and character of sediment supplied to a shore affect a coast's character. -Erosional coasts form where wave erosion washes sediment away faster than it can be supplied; such coasts recede landward and may become rocky if there's insufficient sand to supply a beach. -Accretionary coasts, those that receive more sediment than they lose by erosion, grow seaward and develop broad beaches. Climate also affects the character of a coast. -Shores that enjoy generally calm weather erode less rapidly than those constantly subjected to ravaging storms. -Sediment supply needed is different for calm environment vs rougher climate. -The climate also affects biological activity along coasts. --In the warm water of tropical climates, mangrove swamps flourish along the shore and coral reefs form offshore. --In cooler climates, marshes develop, and in polar regions, the coast may be a stark environment of lichen-covered rock and barren sediment. HERE BEGINS 16.7 Shorelines are not a permanent entity! Coastal storm wings can generate immense waves. These waves cause intense erosion and damage to shorelines. -During some types of storms, the wind, as well as changes in atmospheric pressure, causes sea level to rise to form a mound beneath the storm. This storm surge is independent of waves and tides. When storm surge reaches the coast at the same time as high tide and is accompanied by high waves, sea level temporarily becomes so hight hat ocean water can inundate land far inland of a beach. The backwash of storm waves sweeps vast quantities of sand seaward, leaving the beach a skeleton of its former self. -surfs can submerge and shift barrier islands and can cut new inlets. Waves and wind together can rip out mangrove swamps and marshes and break up coral reefs, thereby destroying the organic buffer that normally protects the coast and leaving it vulnerable to accelerated erosion for years to come. Surf can also undermine coastal cliffs and trigger landslides. Major storms also destroy human constructions: -erosion undermines seaside buildings -Wave impacts smash buildings to bits -Storm surge floats buildings off their foundations. ***danger on coasts leads to residents having evacuation and safety plans. Global sea level is rising by (0.13 in/year) -Already, some coastal cities are enduring flooding during times of particularly high tides, known as nuisance tides, or when storms drive storm surge onto the land. --15% of oceanic islands in the Pacific will be submerged (will affect Gulf and East coasts of the US the most) ---As saltwater encroaches on the land, groundwater may become salty, and as a result, plants without salt tolerance will die off. Solutions to coastal flooding? -Moving towns inland -Adding fill to make the land surface higher -Constructing barriers against the sea -Installing pumps and drainage canals to keep rising waters out Loss of river sediment, a gradual rise in sea level, a change in the shape of a shoreline, or the destruction of coastal vegetation, can alter the sediment budget of a beach. -sediment supply decreasing leads to narrowing beach due to more erosion (or exposes bedrock) -Beach retreat is seen in cliff retreat at the back edge of a beach, which may cause the whole beach to migrate landward. Beach property owners may construct artificial barriers to protect their stretch of coast or to shelter the mouth of a harbor from waves. -Alter the natural movement of sand and can change the shape of the beach. -Building groins-concrete or stone walls perpendicular to shore-to prevent longshore drift from removing sand from a beach. --jetties are a pair of walls at the entrance to a harbor. These effectively extend the river channel into deeper water, which may lead to the deposition of an offshore sandbar. Engineers may also build an offshore wall called a breakwater, parallel or at an angle to the beach, to prevent the full force of waves from reaching the beach. --With time sand builds up in the lee (landward side) of the breakwater, and the beach grows seaward. To protect expensive seaside homes, people build seawalls out of riprap (large stone or concrete blocks) or reinforced concrete on the landward side of the backshore zone. But seawalls reflect wave energy which crosses the beach back to sea, so this process increases the rate of erosion at the foot of the seawall. During a large storm, the sea wall may be undermined so much that it collapses. In some places, people have given up trying to decrease the rate of beach erosion and instead have worked to increase the sediment supply. -Pump sand from farther offshore, or bring it in from elsewhere. --This procedure is called beach nourishment or beach replenishment, it can be expensive and only a temporary fix. (backwash and longshore drift still occur) Because of longshore drift, garbage dumped in the sea in an urban area may drift along the shore and be deposited on a beach far from its point of introduction -Oil spills contaminate shorelines in the same way Organic coasts, a manifestation of interaction between the physical and biological components of the Earth System, are particularly susceptible to changes in the environment. -Loss of these landforms can increase a coast's vulnerability to erosion, and because organic coasts provide spawning grounds for marine organisms, can upset the food web of the global ocean. In wetlands and estuaries, sewage, chemical pollutants, and agricultural runoff cause havoc. -Toxins killing burrowing marine life -Algal blooms due to runoff Many coastal wetlands face destruction by human development: -20 to 70% have been destroyed in the last century for farmland or suburbs, and even garbage dumps. Coral reefs depend on the health of delicate coral polyps. -very susceptible to change!!! --pollutants, particularly hydrocarbons will poison the polyps. -algal blooms -suspended sediment lowers light levels -change in water temperature, salinity, and acidity caused by global warming of the atmosphere In the last two decades, on the order of 50% of reefs worldwide have lost their color and died. -process is called reef bleaching, may be due to the removal or death of symbiotic algae in response to the warming of seawater, or it may be a result of the dust carried by winds from desert or agricultural areas.