Exam 2
discharge, how is it measured?How do discharge rates vary seasonally and along the length of a stream channel?
(Q): stream flow, or the amount of water (volume) flowing past a given point (through a given crosssection) over a specific length of time. Discharge rates tend to be low near the stream's source and increase further downstream as other tributaries feed into the main channel. Discharge, measured in m3/sec = the channel's cross-sectional area * average speed velocity, and may range from 1 cubic meter/sec in a small stream to > 1 million m3 /sec for a large river (m3/s is a volume per unit time).
spring tide
(not related to the season "spring") occur when the sun, moon, and Earth are aligned, tidal extremes are at their greatest.
What options are available to help stabilize a slope and reduce the possibility of future movements?
-Avoid the most landslide-prone areas -Takes steps to control a mass-movement -Rely on geologic survey before construction -Build retention structures into slope -Plan fluid removal or moisture reduction strategies into projects -Drive piles or employ rock bolts on a potential unstable slope -Recognize the hazard
What are some examples of paleo-related proxy data for determining ancient global temperatures?
-Drill into glaciers / ice sheets In Antarctica and Greenland and analyze air bubbles -Layered sediment
What are some strategies for reducing global warming?
-Reduce Fossil Fuel Use -Plant Trees -Reduce Waste =Conserve Water
How does global human population influence global warming?
-burning of fossil fuels
What are some geographic examples within North America of areas whose landscapes have been influenced by glacial activity?
1. The Rocky Mountains (from the Midwest extending all the way to the west coast): many of its peaks and valleys were glacially carved. 2. The Great Lakes: occupy basins carved and deepened by glaciers and filled with glacial meltwater. 3. Canada's Hudson Bay is a depression formed by the weight of the ice sheets and flooded with seawater after the ice melted away. 4. The drainage of the Mississippi R. in part was formed by meltwater from retreating ice sheets. The sediments carried along with that meltwater ("loess" see below) are in part responsible for the fertility of the Midwestern farmland, and supply the groundwater tapped today for irrigation.
Where is most of Earth's water stored? By what means is the rest of it stored?
97.5% of the Earth's water is in the oceans 1.81% is glacial ice 0.63% travels under the ground as groundwater 0.016% is in streams and lakes 0.001% is in the atmosphere
What is a delta and how is one formed?
A large, fan-shaped pile of sediment in still waters created by a stream. When a river drains into the sea, the river's velocity often slows down dramatically. If the river is still carrying a large suspended load, and its velocity drops to near zero its mouth, all the river's suspended sediment is dropped. The resulting fan-shaped pile of sediment t
capacity in relation to streams
A measure of the total load of material a stream can move over a given period of time; depends on discharge, geography, slope, etc.
longitudinal profile
A sketch of a stream's elevation from source to mouth
What is the difference between an active margin and a passive margin? Which characterizes the east and west coasts of North America?
Active margins: the coastline is on an active plate boundary. Example: the western coasts of North and South America is in part both a subduction and a transform boundary. Active margins have narrow continental shelves, and drop steeply and quickly to the ocean depths offshore. Passive margins: the coastline is not on an active plate boundary. Example: the eastern coasts of North and South America (the active margin is the Mid-Atlantic Ridge, a spreading center in the middle of the Atlantic). Passive margins have a wide continental shelf, broad beaches, and sandy offshore islands.
flash flood (upstream flood)
Are a variety of upstream flood. They are a high volume of flooding water in very short duration, characteristic short lag time, usually in upper part of drainage basin. Common in canyons and highway underpasses.
What is the relationship between glacial activity, changes in global sea level, and climate change?
As climate gets warmer, sea levels rise, and glaciers melt
which sediment layer applies to stream channels and why?
Bedload- Large or heavy sediment particles that travel on the streambed (sand and gravel). Bedload moves by traction (rolling, sliding, dragging) or saltation (bouncing).
desert; what are some ways in which deserts form naturally?
Causes of Natural Deserts: 1. High surface temperatures. The sinking cool air at 30°N and 30°S of the Equator results in desert environments due to the cooler air warming as it reaches the surface, taking with it much of the moisture, causing rapid evaporation. 2. Topography. Mountains ranges that lie in the path of air currents may push the air in higher altitudes as the air rises over the range, causing the air to cool and for it to lose its moisture (which precipitates out as rain). As a result, one side of the mountain range is extremely wet, but the opposite side is dry, as the now-dry air forms a rain shadow. Rain shadows are formed by the Sierra Nevada mountains of California and the Cascade Range of the Pacific Northwest (Orgeon, Washington). Elsewhere, the Tibetan plateau creates a rain shadow as air rises up over the Himalaya mountains, as do the Andes Mountains in South America (e.g. Atacama Desert in Chile).
What are Milankovitch cycles?
Eccentricity, Obliquity, and Precession (relate to Earth's position in space, which affects the radiation Earth absorbs) Eccentricity- Earth's orbit is alternatingly round and elongated - 100,000 year cycles - Affects earth long-term and seasonally Obliquity - Axial Tilt Earth's tilt angle varies - controls seasons - higher angle = warmer summers and cooler winters - 400,000 year cycles Precession - "Wobble" Variation in the orientation of Earth's axis - Makes one hemisphere warmer and the other cooler - 26,000 year cycle
What are emergent coasts and submergent coasts, what causes each to form, and what are the characteristics of each? Is global sea-level currently rising or falling? By how much? What is thought to be causing the change?
Emergent coast -Tectonic activity lifts the coast up in the air (uplift)-Mountain range building; 2 factors: Rates of deposition & Rates of sediment deposited on the beach is greater than erosion taking the sediments away. The coastline is submerged by water - erosion; sea level is falling Submergent coast- Subsidence: land is sinking and the sea-level is rising The melting of glacial ice has two potential effects of sea level rise: 1. the release of additional water from the melting glacier back into the ocean accounts for half of global sea level rise, 2. the other half of global sea level rise is attributed to the expansion of water with increased temperatures (thermal expansion).
What forces pull geologic materials downslope?
Falls: free-falling action. E.g., rockfalls. Occur on very steep / near vertical slopes. Common along rocky coastlines that are undercut by wave action, and on steep roadcuts through solid rock. The rubble that accumulates at the base of the cliff is called talus. The cliff over which the water flows at Niagara Falls, e.g., is slowly retreating backward due to undercutting, and a talus slope has accumulated at the base. Slumps and Slides: rock or soil slips downward along a clearly defined surface (a fracture) or bedding plane. Slumps may be planar or rotational (a curved mass of rock or soil moves downslope). Flows and Avalanches: flow - chaotic, disorganized movement, e.g., fluid flow. E.g., snow avalanches, pyroclastic flows (nuees ardentes from Ch. 5 volcanoes), mudflows (earth saturated with water, these include volcanic lahars, also from Ch. 5). A flow involving a variety of materials is called a debris flow / debris avalanche.
How does a glacier form?
For glaciers to form, x conditions must be met: 1. Precipitation: glaciers, after all, are reservoirs of frozen water. 2. A higher rate of snowfall than melt each year. This allows the glacier to grow. 3. Mountains: most glaciers begin in the mountains as snow patches that survive the summer. This is favored on north-facing slopes. 4. Gentle slope: if the slope is > 30°, avalanches may form, clearing the glacier away. The transformation of snow to glacier ice is slow: the process can take decades or thousands of years(depending on the rate of snowfall). Initially, loose snow is 90% air. As more snow is deposited on top of it, the snow becomes denser, more compacted, and turns into firn (25% air); and eventually compacts further to form glacial ice (20% air). Glacial ice consists of interlocking ice crystals. Eventually, if there is a slope, the mass of ice moves, forming a glacier.
glacial striations
Glacial activity often leaves grooves / scratches in rocks that form parallel to the flow direction of the glacier.
U-shaped valley v. V-shaped valley
Glaciers can carve relief into mountainsides and also strip away surface sediments from continents. Like a stream, an alpine glacier carves its own U-shaped valley (whereas the valley carved out by a stream is typically V-shaped). Glacial erosion modifies valleys from V-shaped (the river-channel forms the point of the "V", formed as the river erosion occurs in the channel, and mass wasting causes the valley slopes to approach the angle of repose) to Ushaped (glaciers erode the sides of the valley and also its floor).
How do earthquakes influence slope failure?
Ground movements via seismic waves can induce landslides in hilly areas. The California coast, e.g., is prone to sea cliffs and hillsides prone to landslides during earthquakes. A tragic earthquake-induced landslide occurred in the Peruvian, 1970 (the 7.9-magnitude Ancash earthquake), that killed more than 18,000, burying the towns of Yungay and Ranrachira. Peru, which sits on the west coast of South America, houses the Andes mountains, which are still growing as a result of an active subduction zone off Peru's western shore. The country's highest mountain, Huascaran, destabilized, sending a massive debris flow / avalanche that advanced about 11 miles through valleys before burying the towns below it. Earthquakes may also trigger underseas avalanches along the continental shelf - sending those sediments down the continental slope deep into the ocean depths. These events are called turbidity currents.
downstream flood
Longer duration (the flood lasts longer), greater magnitude, these floods affect a much larger geographic area
By what process do non-polar-based glaciers move / slide? What about within the glacier itself?
Moves due to the force of gravity; slower along edges, faster in center - Few tens of meters per year Glacial surges: tens of meters per day - caused by water flowing under ice, lubricating glacier and causing it to surge forward
drainage divide
Neighboring drainage basins are separated from each other by this
cut bank; where is it formed in a river bed and what kind of flow dynamic is occurring in it (i.e. deposition or erosion)? How do they cause the meandering stream to move over time?
Once formed, the meanders enlarge and move! Erosion on the outside edge of a meander forms a steep cut bank. This erosion occurs because water moves faster on the outside of a bend. With continued erosion, two adjacent cut banks could meet, shortening the river's length and cutting off the meander channel entirely
How does vegetation, or the lack thereof, influence slope failure?
Plant roots help bind soil and prevent flow. Vegetation also takes up moisture from the upper layers of soil, helping to reduce the soil's moisture content (keeps the soil drier) and increase its overall shear strength. On the flip side, plant vegetation also adds mass to the slope, and too much water extraction from the soil can dry it out, increasing the potential slide hazard. For this reason, logging practices in populated come under scrutiny: the removal of the vegetation, along with the creation of logging roads can contribute to landslides.Wildfires frequently strip slopes of their vegetation, decreasing the stability of the slope.
horn
Pointed mountain peak surrounded by at least three cirques (e.g. Matterhorn in Switzerland)
groundwater
Rain that falls onto land and seeps into the ground and travels under the ground
runoff
Rain that falls onto land and travels along the surface of the land
slide v. slump
Slides: rock or soil slips downward along a clearly defined surface (a fracture) or bedding plane -Material moves as cohesive unit along clearly define structure Slumps: may be planar or rotational (a curved mass of rock or soil moves downslope) -Material moves downslope accompanies by rotation
meandering channel
Streams typically wind, or bend, through their course. These bends are called meanders.
What is the greenhouse effect? What gases get trapped? How might this contribute to global warming? What are the Big Three gases that have been contributing to the greenhouse effect?
Sunlight enters the atmosphere and energy is absorbed as heat on the surface. Infrared waves (heat) are radiated off and get trapped by gases in the atmosphere, causing global warming *Greenhouse Effect is a GOOD thing, necessary for life to exist! Water is the most abundant greenhouse gas! It is only a problem when there is too much. It sustains living things on a basic level; main components: CO2 (carbon dioxide), CH4 (methane), N2O (Nitrous oxide - smog)
alpine v. continental glacier; which is more numerous?
The 70,000 - 200,000 glaciers known today fall into one of two categories: 1. Alpine: numerous today, also called mountain or valley glaciers. 2. Continental: larger, rarer these days, aka ice caps or ice sheets. Continental glaciers can span entire continents and reach thicknesses of greater than one kilometer. In the present day, the two main continental glaciers are the Greenland and the Antarctic ice sheets (the latter is larger than the continental US). During the Pleistocene Ice Ages, much of the northern hemisphere was covered in glaciers
How do fluids influence slope failure?
The addition of some moisture to dry soils may increase adhesion, helping the particles to stick together (think how it is easier to build a sand castle with wet sand rather than dry sand). Fully saturated unconsolidated materials, however, have reduced friction between particles, which can lead to destabilization of a slope. Just the mass of added water to a slope adds extra weight, and extra downward pull Water can also seep in between bedding planes in layered rock, making sliding more likely. And repeated freezing and thawing of water in rocks can create wedges that split the rock apart (frost wedging). Some clays, such as one called montmorillonite, absorb water very readily, causing them to swell up, expand, and become gel-like: these clays fail easily under stress. Sudden landslides often involve a triggering mechanism: heavy rainfall, combined with rapid melting of snow led to one of several debris flows in northwestern Washington state in 2009 (see Fig. 8.7).
terminal moraine
The debris deposited by the furthest extent of glacial ice is this
drainage basin (watershed)
The geographical region from which a stream drains its water. It provides the stream with its water source.
What is soil creep? How fast is its movement?
The gradual downslope movement of soil - slow moving; noticeable over time
poorly- sorted sediment layer
The grains in the sediment vary in size
headwaters/ base level
The lowest elevation to which the stream can erode downward
What is desertification and why is it a cause for concern?
The rapid development of deserts (or expansion of existing deserts) caused by the impact of human activities, usually as a consequence of land-use practices. E.g. Dust Bowl of the 1930s in the US Midwest as a result of decades of misguided farming practices that caused the topsoil to erode away. Removing native vegetation and replacing them with crops leaves the land vulnerable to degradation during drier conditions (the native plants would be better adapted to dry conditions); similar results with raising livestock. Desertification reduces the amount of arable land on which the world depends for food.
talus slope
The rubble that accumulates at the base of the cliff is called talus. The cliff over which the water flows at Niagara Falls, e.g., is slowly retreating backward due to undercutting, and a talus slope has accumulated at the base.
oxygen 16
This oxygen isotope is lighter, evaporates more easily from the oceans so the precipitation and glacial ice is enriched in it; warmer water when more of this is present and oxygen 18 is evaporated
load in relation to streams
Total quantity of material carried by a flowing river ◦ (traction, bed- move by saltation, suspended, and dissolved)
How does human activity and development impact landslide frequency? Understand the general role human land use can play in fostering landslides (timber harvesting, urbanization, dam construction, etc.).
Vegetation tends to stabilize slopes Re-plant areas affected by wildlife immediately Avoid over steepening of slopes Increase shear stress and mass wasting hazards Place additional supporting material at lower end of suspected area Reduce the load of the slope Avoid over watering scenarios Leaking pools and water pipes, excess watering of landscape, or installing a poorly placed septic tank drain fields Plan to build away from slopes with mass wasting potential
point bar; where is it formed in a river bed and what kind of flow dynamic is occurring in it (i.e. deposition or erosion)? How do they cause the meandering stream to move over time?
Water moves more slowly on the inside curve of a river bend. When water velocity slows down, sediment is deposited. Deposition on the inside edge of a meander forms a sandy wedge-shaped structure called a point bar.
Understand the general dynamics of wave motion and how this changes as the wave moves from deep water to shallow water as it approaches the beach. What happens to the wave with regard to size, shape, and speed as it moves from deep to shallow water?
Waves are created by the flow of wind across the water's surface. In the open ocean, wave motion along the ocean surface is roughly circular (a cork would bob up and down as a wave passed it). As the wave approaches the shallower water by the shore, it "feels bottom" and its circular orbits become more elliptical, ultimately flattening to a forward / back motion. As waves move into shallower waters, the wave length and velocity decrease, wave height increases, and the wave "breaks forward" (topples due to instability), its energy spent along the shore.
middle (or medial) moraine
Where two valley glaciers merge, the debris in the two lateral moraines merge to become this, which is often seen as a stripe running down the composite glacier.
What is an alluvial fan and how is it formed?
a delta that forms when a stream flows from the mountains (high velocity, steep gradient) onto the open plains (low velocity, shallow gradient: as the stream transitions to the plains, the river channel becomes wider, shallower, and has a shallower slope; this change decreases the velocity of flow, causing deposition of sediment.).
landslide
a general term to describe rapid mass movements. In the US, landslides cause $3.5 billion in property damage annually, and result in 25-50 deaths. There are several landslide-prone regions of the US.
debris flow
a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity.
hydrosphere
all the water at and near the surface of the earth; the amount is essentially constant
sea cliff
an erosional landform, produced by wave action, which is either at the seaward edge of the coast or at the landward side of a wave-cut platform and which denotes the inner limit of the beach erosion.
What evidence is there to support a recent rise in global temperature?
as a result of human activities, the present carbon dioxide level is about 30 % higher than its highest level over the past 600,000 years
circque
bowl-shaped depression that develops on the side of the mountain at the head of a glacier
How can land use changes affect stream bed dynamics (e.g. transitioning from a forested environment to an agricultural one, and vice versa; or regulating discharge by building a dam) ?
cause earthquakes, decrease the ability for animals and humans to navigate, change in base level, reshaping of the stream channel
braided channel
common type of river channel found where the sediment load is very large. Small islands can form in the middle of the streambed, forcing the river channel to divide and rejoin in a braided pattern.
How do dams, levees, and channelization influence a stream's long-term dynamics?
dams-can help minimize flooding by controlling the rate of a stream's discharge. Damming also creates an artificial lake that may be used for recreational purposes, and can also serve as a source of hydroelectric power (reducing the reliance on fossil fuels). The downside to dams is that they can disrupt fish migration routes, and the artificial lake that forms behind the dam destroys the local ecosystem. Sediment loads also build up behind the dams, which then needs to be dredged, and the lack of sediment (as a means of replenishment) downstream of the dam causes increased rates of erosion for the streambed. Some large dams, such as the Hoover Dam in Nevada, have even been found to cause earthquakes (the water behind the dam represents an added load on the rocks, increasing the stress on them). levees- ridges that form along banks of a river. Artificial levees are a constructed form of the natural levee, used for flood control. The drawback is that the river water, by being shunted, no longer floods the floodplain. Flood risk increases further downstream, and channels much be dredged periodically channelization- increase discharge by increase either the velocity of water flow and/or the volume of the channel. In doing so, surplus water is carried away at a faster rate. The channel can be widened or deepened.
berm
flatter part of the beach, just above the high tide mark (the last part of what you would walk on before arriving to the water). Behind the berm are typically sandy dunes, or cliffs, low-lying land, or artificial structures such as seawalls. Berms are often features of beaches in the summertime. In the winter, stronger and higher tides and wave activity seasonally erode them away.
How has global warming affected arctic sea ice / glacial deposits / sea level?
flooding, increased shoreline erosion and saltwater encroachment, thermal expansion, melting glaciers
What is a beach? What is the prime mineral(s) that makes up a typical sandy beach?
gently sloping surface washed over by waves and covered by sediment. The sand that makes up the beach can have three possible origins: 1. washed up by the waves as the tide rises and falls. 2. transported by wind from behind the beach. 3. deposited on the coast by streams (rivers) or coastal currents.
What is the ocean conveyor belt and how does it influence regional temperatures?
global circulation of ocean waters, contributes to the change. The Gulf Stream (not to be confused with the Jet Stream, a wind current) is part of this larger belt, whereby warm surface water is transported west and north to Greenland, where it cools from contact with cold Canadian air (called downwelling). As the water cools, it increases in density and sinks to the bottom, then flowing south, then further east to the Pacific, where upwelling occurs. • The heat released to the atmosphere from the Gulf Stream helps keep Northern Europe at least 10°F warmer than it would be if this thermohaline circulation pattern was not present. Abrupt historical changes (which, to a geologist, means decades / centuries scale) in climate are sometimes attributed to disruption in currents such as the Gulf Stream (e.g. melting Greenland ice sheet would cool the Gulf Stream waters, disrupting the circulation pattern).
littoral drift
gradual transport of sand in a saw-tooth or zig-zag pattern in the same direction as the longshore current as a result of the different directions of the incoming wave (coming in at an oblique angle) and the outgoing wave (which is pulled straight out directly down the slope of the shoreline). Over time, sand is moved from one end of the beach to the other, resulting in a need to keep replenishing the beach sand in order to maintain the beach.
groins and breakwaters
groins: solid bars that run out perpendicular to the shoreline breakwaters: same idea, but they typically run parallel to and offshore from the shoreline (up to a few hundred meters offshore). Both are built to reduce the erosion of sand from the local beach. The long-term effect of these structures, however, is to deprive the neighboring beaches downshore of their sand supplies; thus hastening erosion of the neighboring downshore beach. With jetties, the beach region behind the jetty starts to build up unnaturally (because the jetty limits the erosion of the beach it is protecting) relative to the areas not protected by the jetty, so that the beach ultimately builds out to the jetty.
mass wasting
he downslope movement of geological materials (e.g. rocks), usually due to gravity. The movement can be slow or sudden. The movement is not restricted to sliding down a slope: any vertical movement of land, such as sinkholes or surface subsidence would qualify.
oxygen 18
heavier oxygen isotope; increases in cooler temps in sea water
bed load
intermediate size material. These materials may be carried in short hops along the stream bed, a process called saltation
What is the angle of repose?
is maximum slope angle at which dry, unconsolidated material is stable.
oxbow
isolated meander forms this
How does undercutting make a slope unstable?
it serves both to increase the gradient of the slope, reducing stability, and to remove toe weighting, which also decreases stability
non-structural strategies
land-use restriction, development prohibition or set-back from the beach (equivalent to restrictive zoning along a floodplain)
What influences the temperature of the Earth?
latitute and altitude; sunlight received - amount of solar radiation reflected - albedo (cloud cover, glacial ice, atmospheric particles, etc.), heat retention by atmosphere (infared radiation)
storm surge
like a low-grade tsunami: a mound of water is pushed onshore by a strong storm. A surge can combine with storm-related wave action and increased wave height can wreak havoc on a coast, particularly if the surge coincides with high tide.
barrier islands
long, narrow islands paralleling a coastline and somewhat offshore from it. Why / how they form is not known. They provide protection for the mainland by taking the brunt of the incoming wave energy, especially during storms. Because of their low relief, however, they may easily become submerged during a high storm tide, as can occur during hurricanes.
What is a glacier? What conditions are needed to form one?
masses of ice that move under their own weight, under the force of gravity. Glaciers can take several centuries to form (and melt), and are associated with high latitudes (e.g. Alaska) and/or high altitudes (e.g. Mt. Kilimanjaro, in Tanzania, which lies near the equator).
stabilization
measures to try and limit beach erosion, at least temporarily
neap tide
occur when the sun and moon are at right angles to each other, the difference between high and low tide is minimal.
tides
periodic rise and fall of water levels due to the gravitational pull of the sun and moon on the oceans. The oceans "bulge" on the side of the Earth nearest the moon (and a complementary bulge on the opposite side of the Earth). At high tide, the waves reach higher up the beach face; at low tide, more of the beach face is exposed
longshore current
poduced by incoming waves striking the coast at an angle (this type of current does not occur if waves strike the beach perfectly parallel). The longshore current is a flow of water flowing parallel to the shoreline in the surf zone (this current tends to pull you further down shore if you play in this portion of the water)
beach face
portion regularly washed by the waves as tides rise and fall
zone of ablation
removal of ice; involves three processes: 1. Sublimation: evaporation of ice into water vapor 2. Melting: transformation of ice into water 3. Calving: breaking off of chunks of ice at the end of the glacier into smaller pieces
glacial till
sediment transported by ice and deposited beneath, at the side, or at the toe of a glacier. The sediment is usually poorly sorted compared to stream-deposited sediment: glacial ice can carry clasts of all sizes. When till mixes with meltwater, the result is called outwash. Till and outwash are two types of glacial drift
What two forces resist that geological pull downslope?
shear strength: cohesion - ability of particles to attract and hold each other together) and friction - friction between grains within a material
zone of accumulation
snowfall adds ice to a glacier
seawalls
solid concrete walls often placed at the base of a cliff to break the force of the wave impact and minimize erosion (and the retreat) of the cliff.
What is a stage and a crest in the context of flooding?
stage - the height of the water level in a river at a given location at a given time crest - it is the highest stage or level of a flood wave as it passes a particular point.
discharge in relation to streams
stream flow, or the amount of water (volume) flowing past a given point (through a given crosssection) over a specific length of time
dissolved load
substances that completely dissolve in the water [e.g, bicarbonate (HCO3-), sulfate (SO4 2-),calcium (Ca+), sodium (Na+), magnesium (Mg+)]
What is wave refraction? What happens to wave energy as waves meet a sea cliff that juts out from the shore line?
the deflection of the incoming waves toward the headlands (areas of the coast that just out into the ocean) 1)The waves erode and undercut the base of the cliff using hydraulic action and abrasion 2)A wave-cut notch is formed at the base of the cliff, between the high and low water marks, which undermines the rock above 3)The face of the cliff falls down 4)A wave-cut platform (or rock platform) is formed as the cliff retreats Examples: Near Ballybunion, Co. Kerry; near Tramore, Co Waterford; Cliffs of Moher, Co. Clare
hard structural stabilization
the emphasis is on "hard" objects, such as sea walls, rip-rap, groins, and jetties.
soft structural stabilization
the emphasis is on sand replenishment and dune rebuilding
floodplain; how are they produced?
the flat surface adjacent to either side of the river that is periodically inundated by floodwater. Floodplains are produced by flooding. Flooding and floodplains are natural aspects of stream processes and evolution.
saltation
the movement of hard particles such as sand over an uneven surface in a turbulent flow of air or water
lateral moraine
the side edge of the glacier
slope/ gradient
the steepness of a stream channel, calculated as the difference in elevation between two points along a stream, divided by the horizontal distance between them along the stream channel (i.e. "rise" over "run"). The higher the gradient, the steeper the channel, the faster the stream flows. They are usually highest (steepest) near a river's beginning (the source) and tend to decrease downstream. Near the end of the river, or mouth, of the river, gradients are at their lowest, as the river has reached its lowest elevation, or base level. Usually, base level = sea level.
glacial v. interglacial period
the time between when glaciers retreat and advance is called an interglacial period. In our current geologic epoch, called the Holocene, we are currently considered to be in an interglacial period because the glaciers are still present (though rapidly retreating)
suspended load
tiny, solid grains of silt and clay, carried by the flowing water above the streambed. When rivers appear brown (e.g. during flood season), it is because the suspended load of that river is high.
hydrologic cycle
water circulates in this cycle: In this cycle, ocean water evaporates into the atmosphere. The water in the atmosphere ultimately precipitates out as rain. Rain that falls onto land either i) seeps into the ground and travels under the ground as groundwater or ii) travels along the surface of the land as runoff. Either way, the water ultimately drains back into the oceans, usually via streams, and the cycle continues
well-sorted sediment
where all the sediment particles are the same size in a particular area
estuaries
where freshwater rivers and the rising and falling saltwater tides create a zone of brackish water (Chesapeake Bay, Long Island Sound, Puget Sound, San Francisco Bay, etc.). Many vital wetlands are estuaries, but these areas are also under pressure to be dried out to provide room for urban development.
dune; how do they move?
wind deposition creates these, usually made of sand, but snow dunes are also possible. The orientation of them reflects the prevailing wind direction (if there is one), which the shallower slope side facing upwind. If there is a strong enough prevailing wind direction, a dune can migrate: its particles get blown up the side of one shallower surface and slide down the steep slip face. As layer upon layer of sediment slides down the slip face, slanted crossbeds develop in the dune.
interpret flood frequency curves and how to interpret the predictions made by reading them (i.e. what does the phrase "100-year flood" mean? What is the probability that the 100 year flood will occur in any given year?). i.e. recurrence intervals
Recurrence interval: the average time interval between actual occurrences of a flood event (or other event); the average interval in which a flood of a given size is exceeded as an annual maximum. R = (N + 1)/M, ...where N as the number of years of record, M is the rank of individual flow within the recorded years. E.g. say a stream's annual discharge is recorded for 100 years. The number for each year is ranked from 1- 100, with 1 being the lowest annual discharge, 100 being the greatest annual discharge. Each of those numbers represent an M value. So if M = 1 (the smallest annual discharge for a certain year), R = (100 + 1)/100, or 1.01. If M = 100, R = (100 + 1)/1 = 101. The probability of a given magnitude flood in any given year is P = 1/R ...again, using the values from above, if M=1, R = 1.01, P = 1/1.01 or 0.99. I.e. there is near 100% certainty that the stream will discharge this amount of water in any given year (as this is the minimum flow level recorded over a 100-year period). If M=100, R = 101, P = 0.009. I.e. there is a 0.9% (~1.0%) chance of a discharge value this high in any given year. This would be called the 100-year flood (1 in 100 chance).
How do volcanic eruptions affect global temperatures?
Release gases, some of which are greenhouse gases that warm the environment, but the dominant effect is cooling because of the sulfur gases
