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Chapter 3: Sediments and Rocks: materials of coastal environments

Rock Types

Sediment Properties

Relevance to coastal dynamics and coastal processes

Rock Types

Igneous:

Comprise most of the crust

Formed from magma within the mantle

Silicate minerals (cations + charged ions with silicon and oxygen (SiO4 or 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 light

Oceanic CrustPrimarily basaltic (Fe, Mg, Ca, low SiO2)7km thickRelatively dense

Rock Types

Sedimentary:

Physical, chemical, biological, weathering breaks rocks into small particles (sediments)

Transported (wind, water)

Deposited

Burial and cementation (sandstone, mudstone)

Rock Types

Metamorphic:

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 types

Sediments

Sediments compose most of the coastal environments that we will discuss in class

bluffs (boulder, cobbles, sands)

barriers/barrier islands (sands)

bays/lagoons (fine sands, silts, clays)

wetlands (silts, clays)

estuaries (silts, clays, possible sands)

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Sediment Size ClassificationWentworth grain-size scale

(Wentworth, 1922).

Grain Size Distribution Curves

Mean: statistical average

d50: grain size

Well sorted: narrow distribution of grain sizes (B)

Poorly sorted: broad distribution of grain sizes (C)

Relevance To coastal dynamics and processes Bluff Erosion

Offshore Glacially Deposited Sand Ridges, Relict Ebb Shoals

Sources of Sand For Littoral Transport

2 m

Tide Dominated &

Riverine

Wave Dominated

Mixed Energy

Gravel

Sand

Barrier Island

Cliff or Bluff Coast

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Maximum 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)

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Calculated Recession Rates for Montauk Bluffs

McCormic & 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 – 199581,100253,5500.950.29

yd3/yryd2ft3/yrm2/yr

ReferenceYearsLit. Cont.SARecession Rate

Atlantic Coast of New York Monitoring Program

Seasonal Profiles 1995 through 2004

Measured Recession Rates and Littoral Drift Contribution for Montauk Bluffs

3411754151Total0.97Average608296540.810.91M43567090004.451.30M4291614530.620.31M41

190030151.200.20M4072511500.402.00M39

11034175147.801.90M38166326401.200.83M37612797253.200.32M35

Littoral Volume yd3/yr

Integrated Volume yd3/yr

Vol. Change yd3/ft/yr

Recession Rate ft/yr

ACNYMP Station

6 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 shelf

Shoreline Retreat During The Flandrian Transgression

-50 m -40 m -30 m

-20 m -10 m 0 m

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•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 Composition

Wave driven transport and

winnowing

River and Raritan Bay Sediments

Raritan Bay Sediments