Coastal Quiz 3

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What are the minerals that typically found in beach sand?
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Terms in this set (43)
What are the minerals that typically found in beach sand?
Quartz, feldspars, heavy minerals (hornblende, garnet, epidote, tourmaline, zircon, and magnetite) and carbonates
What coastal sediments are the most resistant to breakdown in transport?
Quartz is very resistant, feldspar breaks down easily.
What can be inferred from the distribution of beach sediment composition about its source?
felsic source rock- siliclastic beach
mafic source rock- heavy mineral beach
determination of original source based on beach deposits is provenance study
Know how to use the Wentworth scale and the "phi" relationship for calculating grain size.
Wentworth scale goes by powers of 2 (moves from coarse ness, boulder, fine sand, silt, etc.)
Phi scale- coarser grains have a more negative value (Boulder=-20, clay=14)
How does grain shape differ from grain roundness?
Roundness:: angularity and sphericity
Grain shape: ratios of 3 axes
Distinguish the various "measures of central tendency" for a sediment sample
Mean (avg size) Median (50% coarser, 50% finer) and Mode (most frequently occurring size class)
What about the energy in the nearshore is reflected in the cross shore distribution of sediment size?
Low energy nearshore: gently sloped, fine grained beaches
High energy nearshore: steeply sloped, coarse grained beaches
How would you expect the shape of beach sediment to change with distance (alongshore) from its source river mouth?
Sediments are coarse at the mouth of the river/beginning of littoral zone, and get finer and smoother the more they move in the longshore current
How does the concept of hydraulic equivalence factor into creating thin, dark layers of mafic sand in the strata of a largely felsic beach
hydraulic equivalence: density and shape, will it be held aloft or settle into the bed. Why concentrated heavy mineral bands settle
How does density of water change with temperature and why does ice float?
Fluid mass per unit volume has a temperature dependence, increasing with decreasing temperature to a maximum at 4◦C. Obviously, this behavior reverses at lower temperatures because ice floats in your drink.
Density also has a pressure dependence, although often the fluid is under uniform pressure in the coastal ocean and can thus be considered incompressible.
what does this eq say about an incompressable Newtonian fluid τ = µ(du/dz)t= shear stress mu= molecular viscosity z= vertical position u= horizontal velocity molecular viscosity is proportionality constant in the relationship between shear stress and fluid deformationdistinguish steady flow from uniform flowsteady flow- 0 temporal acceleration, change in flow velocity with time du/dt uniform flow- 0 spatial acceleration, change in flow velocity with distance du/dxExplain how the Reynolds Number is used to distinguish flow regime?Reynolds number outlines the parameters for laminar and turbulent flow. Ratio of inertial forces to viscous forces. Demonstrates a property of the flow Re = ρul/μ (p-density, u-velocity, mu-viscosity) Re>2000 turbulent transitional Re<500 laminarHow does eddy viscosity differ from dynamic (molecular) viscosityEddy viscosity caries with flow conditions and increases with turbulence add eddy viscosity ζ number to molecular visc mu τ = (μ + ζ) du/dzWhat does the "Law of the Wall" describe?velocity profile within the logarithmic layer u = (u∗/κ) ln(z/zo) τb = ρ(u∗^2) allows estimation of bed shear stress from velocity profileHow, and why, do sediments finer than 63 µm behave differently from coarser sedimentsif the sediment is under 63 mumeters, cohesion and floccuation dominate, seds stay suspended. Coarser sediments can use physics to est entrainment and settling velocityStudy the diagram showing the "Torque Balance on a Grain". Understand the difference between torque and forcetorque works to pivot grain out of it's spot (lift and drag forces) must be applied with a lever arm length, movement happens when torque to rotate grain exceeds torque to keep it in place, force acts on the grain, lift drag and gravitational forceHow does pivot angle factor into entrainment potential with regard to size distribution of sediments on the sea bed (or a river bed for that matter)Bee bees and basketballs. bee bee resting in basketballs, pivot angle is much higher and grain will hide between the large cavities between basketballs making it much more difficult than predicted to be entrained. basketball on bee bees, pivot angle is decrease, easy to move a basketball over a bed of bee bees, takes much less energy to move a grain of that sizeBe able to distinguish bedload from suspended loadbedload- rolling, trundling, saltating grains in regular contact with the bed suspended load- sed held aloft by turbulence, does not touch bedWhat forces are balanced when a sediment grain reaches constant terminal settling velocity (CTSV)? Is the grain accelerating when it is at CTSV?Fall velocity/ terminal velocity. Force down= Force upwards, Force drag= Force gravityDescribe the relationship between settling velocity and grain sizesettling velocity increases as grain size increasesHow can bedforms be used to help interpret sedimentary strata in the rock record?bedform morphology is related to sediment size, bed shear stress, and asymmetry of the flow. Certain sedimentary facies are diagnostic of the environment of depositionWhy is transport offshore during storms and onshore during milder conditions?during storms, sediment is stored in offshore bars at depths below the influence of storm waves, then moves onshore during quiescent conditions when wave vortex can reach sedimentIdentify the two longshore sediment transport processes we discussed in class and explain how they differ.Beach Drift- saw tooth pattern of transport caused by an oblique swash and a perpendicular backwash due to gravity ON BEACH FACE(important on narrow wave break beaches, steep foreshore, plunging breakers) Surf Zone Transport- Longshore current caries sed entrained in wave motions BETWEEN BREAKERS AND SHOREBe able to convert longshore transport rates from units of m3/yr to m3/minute. How much is 500,000 m3/yr in m3/hr?500,000 m3/yr = ~1,370 m3/day = ~57 m3/hr = ~0.95 m3/min. x/365=day x/24=hour x/60=minCan accumulation rates be used to estimate gross or net longshore transport rates? What's the difference?Net sediment transport can be estimated by repeated measurements of topographic change on the beach and in the surf zone. Change in sediment volume over known period of time provides net accumulation rateStudy the equation of Inman and Bagnold (1963) that relates longshore transport to wave energy flux. Be sure to understand how it relates longshore sediment transport to the following factors: wave height (H), wave speed (C), and wave breaker angle (αb).PL = (ECn)b sin(αb)cos(αb) L = K(PL) E=(pgH^2)/8 Cn= gT/2piBe able to predict shoreline change from spatial gradients in longshore sediment transport.we should not expect high wave energy flux alone to cause shoreline change (erosion), as is typically thought The spatial derivative (or alongshore gradient) in LST produces a pattern of retreat at the headland and deposition within the bay - as expected, the coast should smooth in response to the imposed wave pattern.What are the sources, pathways, and sinks within a littoral cellSources- River mouth, runoff area Pathways- areas of coast between source and sink where longshore transport occurs Sinks- Underwater canyon or depositional feature (spit)What is the beach profile? Be able to discuss the various methods, discussed in class, available to collect a beach profileBeach profile line traced following the profile of the beach. Dynamic personality of the beach. Sand moves on and offshore with wave energy Emery board, CRAB, surfrover, DGPS profile, video (argus)What is the general shape of the equilibrium beach profile and how does the shape change when the exponent changes?h=Ax^(2/3) h=depth. x=offshore dist, A=coeff (related to grain size) increasing A increases concavity making beach steeper and more reflective, low A= shallow beach, disspativeWhat is the basic justification of Inman et al.'s (1993) conjoined beach profile?produced a subtidal bar. accounts for different processes that dominate in the shore-rise and bar-berm portions of the profile; Shoaling, unbroken waves and broken wave bores. Constraint introduced in this concept is that the volume of erosion on the upper portion of the beach profile is equal to the volume of deposition on the lower portion of the beach profile, as profile migration proceeds landward.Discuss the "Bruun Rule", it's utility, and why it may be controversial?"As sea level rises, shoreface profile adjusts by rising and moving landward by coastal erosion, whilst maintaining its equilibrium shape" It cant predict shoreline behavior under rising sea level conditionsIdentify the following components of the beach profile: beachface, berm, berm crest, beach step.Explain the theory for the relationship between beach slope and sediment grain size.coarser beach should have steeper slope. This is because of infiltration, if uprush water infiltrates in coarser sediments, the backwash is less energetic. Well sorted beaches should have steeper slopes as well.Be able to discuss the relationship among wave energy, beach slope, and sediment grain size, which was revealed by Bascom's (1951) study at Halfmoon Bay, California.beach slope decreases with decreasing grain size (and vice versa). high energy beaches tend to have lower slopes for the same grain size. Gently sloped fine grained beaches at sheltered end, steeply slope coarse grained beaches as exposed endWhat does the elevation of the berm crest represent?flat portion of the beach, coincides with wave runup heightUnder what circumstances might one expect to see a "seepage face" on a beach?"wet beach face" hydraulic gradient of the groundwater table may exist leading to seepage face at the dune's toe. walkable part of the beach, saturated.What are beach cusps?arc patterned(embayments and horns) created by swash motions. Could be a result of nearshore trapped edge waves which travel parallel to beach trend, or could be self organized, resulting from feedback between morphology and swash motions.When would we expect a beach profile to exhibit bars within the subtidal portion?bars encourage energy dissipation, fall velocity parameter Ω = Hb/wsT omega>1 unbarred, omega<1, barred ws=settling velocityRecapitulate the "Bar Formation by the Breakpoint Hypothesis".seaward of breaker zone, sediment transport is in landward direction under shoaling waves, Wave setup in surf zone produces a seaward motion of sediment. Where these two systems interact, sediment accumulates and forms a bar.Be able to identify the stages in Wright and Short's (1984) morphodynamic model of the ideal accretionary sequence.Initial Stage: Longshore Bar and Trough (LBT) built during an extended period of storm conditions of high, steep waves. 2nd Stage: Rhythmic Bar and Beach (RBB) develops during extended period of lower wave height, long-period swell, where bar migrates landward. 3rd Stage: Transverse Bar and Rip (TBR): rhythmic/crescentic bar attaches to beach through transverse bars separated by rip channels fostering strong rip cell circulation Final Stage: Transverse Bar and Rip (TBR): bars weld to beach to form steep, high bermDescribe the sediment exchange system among dunes, the intertidal beach, and the subtidal bars.Dune material washes out into subtidal bars during energetic wave conditions (storms), eroded dune material is stored in the nearshore and slowly makes its way landward during calmer conditions. Moves from dunes, to bars, up the intertidal beach and wind blows sediments back into dunes.