1Chapter 3: Sediments and Rocks: materials of coastal environmentsRock TypesSediment PropertiesRelevance to coastal dynamics and coastal processesRock TypesIgneous: Comprise most of the crustFormed from magma within the mantleSilicate minerals (cations + charged ions with silicon and oxygen (SiO4or SiO2).Iron (Fe), magnesium (Mg), potassium (K), calcium (Ca), sodium (Na), aluminum (Al)Layered Structure of EarthContinental Crust: Primarily granitic type rock (Na, K, Al, SiO2)40km thick on averageRelatively lightOceanic CrustPrimarily basaltic (Fe, Mg, Ca, low SiO2)7km thickRelatively denseRock TypesSedimentary: Physical, chemical, biological, weathering breaks rocks into small particles (sediments)Transported (wind, water) DepositedBurial and cementation (sandstone, mudstone)Rock TypesMetamorphic: Heat and pressure alter original rock structure (slate)Occurs ‘in situ’ or in place. Rocky Coasts can contain any or all of the three basic rock typesSedimentsSediments compose most of the coastal environments that we will discuss in classbluffs (boulder, cobbles, sands)barriers/barrier islands (sands)bays/lagoons (fine sands, silts, clays)wetlands (silts, clays)estuaries (silts, clays, possible sands)2Sediment Size ClassificationWentworth grain-size scale (Wentworth, 1922). Grain Size Distribution CurvesMean: statistical averaged50: grain size Well sorted: narrow distribution of grain sizes (B)Poorly sorted: broad distribution of grain sizes (C)Relevance To coastal dynamics and processesBluff ErosionOffshore Glacially Deposited Sand Ridges, Relict Ebb ShoalsSources of Sand For Littoral Transport 2 mTide Dominated &RiverineWave DominatedMixed EnergyGravelSandBarrier IslandCliff or Bluff Coast3Maximum Amount of Material Derived From Bluff Erosion•Historic estimates 81,100 yd3/yr to 132,100 yd3/yr•The bluffs at Montauk Point are receding at 1 ft/yr •This recession rate has been well documented due to endangerment of the historic Montauk Light House constructed in 1796. •Analysis of the bluff composition and historic rates of recession have determined Montauk (Ronkonkoma Moraine) bluffs could not account for all of the material contained within the littoral system. •Based on sieve analysis data •63-percent of the size fraction (by weight) is similar in composition (fine to medium sand) to the barrier beaches to the west •Littoral Transport reaches a maximum rate of 463,015 to 601,657 yd3/yr at Democrat Point (Fire Island Inlet)4Calculated Recession Rates for Montauk BluffsMcCormic & Pilkey1796 – 199676,065253,5501.000.30Kana, 19951955 – 1979132,100253,5501.560.47USACE, 199539,000253,5500.460.14Rosati et al, 19991983 – 199586,600253,5501.020.31Rosati et al, 19991979 – 199581,100253,5500.950.29yd3/yryd2ft3/yrm2/yrReferenceYearsLit. Cont.SARecession RateAtlantic Coast of New York Monitoring ProgramSeasonal Profiles 1995 through 2004Measured Recession Rates and Littoral Drift Contribution for Montauk Bluffs3411754151Total0.97Average608296540.810.91M43567090004.451.30M4291614530.620.31M41190030151.200.20M4072511500.402.00M3911034175147.801.90M38166326401.200.83M37612797253.200.32M35Littoral Volume yd3/yrIntegrated Volume yd3/yrVol. Change yd3/ft/yrRecession Rate ft/yrACNYMP Station6 to 29 % of Longshore transport at Fire Island Inlet. The Flandrian Transgression•Current sea level rise which began approximately 18-19,000 years ago (during latest Pleistocene time and continuing progressivelyduring Holocene time to the present). •This rise in sea level is directly related to the melting of continental polar and mountain piedmont glaciers. •During the "climax" of the Wisconsin glacial advance (lowstand) sea level was anywhere between 70 to 150 meters below its current level •Shelf Break = the outer edge of the continental shelfShoreline Retreat During The Flandrian Transgression -50 m -40 m -30 m-20 m-10 m0 m5•30 kilometer wide band of sand ridges on the middle continental shelf represent a broad band of degraded and submerged barrier islands formed between 14,000 and 8,000 years before present (Stubblefield, et al. 1983) •Shelf currents are actively reworking the barrier sands into ridges •It has been in the last 4000 years that the majority of modern coastal barrier islands and tidal wetlands have developed.109,868 to 517,948 yd3/yr of sediment may be coming from offshore, however the exact mechanism for the material transport into the littoral zone has not been determined (Schwab et al., 1999) Additional Metropolitan Beach CompositionWave driven transport and winnowingRiver and Raritan Bay SedimentsRaritan Bay