Chapter 5

Chapter 5 - Hurricane Ike moderate strength but unusually...

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Hurricane Ike – moderate strength but unusually large
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30 foot wave
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For comparison, Rita had a surge of 8’ and was terribly devastating for this region
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20 ft surge This morning at 11 am, the storm surge was already 5-7 feet, 200 miles away from the storm – most of Galveston is currently underwater and none of the key factors are even in place yet
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Marine Sediments Classifications – grain size and origin Sedimentation rates and controls Distributions
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Classification of marine sediments can be based upon size or origin. Size classification: divides sediment by grain size into gravel, sand and clay. Origin classification: divides sediment into five categories - Terrigenous sediments, Biogenic sediments, Authigenic sediments, Volcanogenic sediments and Cosmogenic sediments. 4-1
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The Wentworth Scale – for size classification Seives for separating sediments can be bought in these sizes
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Factors that control sedimentation include particle size and the turbulence of the deposition environment. Terrigenous sediments strongly reflect their source and are transported to the sea by wind, rivers and glaciers. Average grain size reflects the energy of the depositional environment. Hjulstrom’s Diagram graphs the relationship between particle size and energy for erosion, transportation and deposition.
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Hjulstrom’s Diagram
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Upward fining – what does this indicate? Upward coarsening – what does this indicate? Graded bedding – causing by hydraulic regime changing with time
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Shelf sedimentation is strongly controlled by tides, waves and currents Shoreline turbulence prevents small particles from settling and transports them seaward where they are deposited in deeper water (Sorting). Particle size decreases seaward for recent sediments. Past fluctuations of sea level has stranded coarse sediment (relict sediment) across the shelf including most areas where only fine sediments are deposited today. 4-2
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Changing grain size of shelf sediments with distance offshore and depth Coarse Fine
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Sea-level drop during glaciation - - - Relative sea level This shows sea level drop for only the last glaciation cycle. Many more came before.
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Sea-level change over past half- million years
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Coastline change during past glaciation
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Glaciers – very effective sediment movers in high latitudes
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“Relict” deposits on the shelf Rapid rise in sea level didn’t allow shelf sediments to equilibrate with the new conditions
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Chapter 5 - Hurricane Ike moderate strength but unusually...

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