1 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 (SiO 4 or SiO 2 ). Iron (Fe), magnesium (Mg), potassium (K), calcium (Ca), sodium (Na), aluminum (Al) Layered Structure of Earth Continental Crust: Primarily granitic type rock (Na, K, Al, SiO 2 ) 40km thick on average Relatively light Oceanic Crust Primarily basaltic (Fe, Mg, Ca, low SiO 2 ) 7km thick Relatively 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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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).
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
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)