Shores and Coastal Processes

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• Chapter 17
• Shores and Coastal Processes

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Shores and Coastal Processes

• Shorelines are places where bodies of water meet
  dry land
• Coasts are landward of ocean shorelines
• Beach a narrow strip of land, washed by waves or
  tides .
• Ordinary Waves are caused by WIND
• Waves are produced when wind drag causes the
  surface water of oceans/lakes to rise and fall
• - Waves get refracted on approaching
  shoreline

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Typical Coast
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Parts of A Wave
Waves are caused by _____________?
Fetch Southern Ocean, Straits of Magellan
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Oscillatory and Translatory Motion
Translatory motion re-suspends sediment
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Wave Refraction
Still a small longshore component
swash
backwash
Kids at the beach
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Shores and Coastal Processes

• Longshore current is produced as water flows
  parallel to coastline
• Rip Currents are produced when water piles up in
  surf zones and flows seaward, generally
  perpendicular to the coast.

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Longshore Currents (Swash and Backwash)
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Rip Currents
Cut in Bar
Sand Bar
Sand bars are big ripples storms cut them,
causing a rip channel
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Tides Mostly the Moon

• Daily rise/fall of surfaces of oceans/lakes due
  to gravitational pull of the Moon/Sun on the
  Earth also due to force created as Earth spins
  on its axis
• Flood tides- elevate sea surface that cause
  shoreline to move inland
• Ebb Tides- low sea surface that cause shoreline
  to move seaward

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Tidal Bulges
Affect of the Sun Much less
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The Effect of Tides On Shorelines
Tides mostly caused by the Moon
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Large Tidal Extremes

• Bay of Fundy tides reach16 m (about 53 ft) at the
  head of the bay. The 12.4 hour period of the
  twice daily lunar tides is close to the natural
  back and forth sloshing period of the bay.

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The Effect of Tides On Shorelines River Hebert
in Nova Scotia
Tidal Bore
Anecdote local tidal bore
Source Clyde H. Smith/Peter Arnold, Inc.
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Low Tide at Bay of Fundy
Source William E. Ferguson
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Rising Tide at Bay of Fundy
Maximum
Source William E. Ferguson
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Coastal Erosional Features

• Wave erosion occurs when deep water waves hit the
  shore with full force
• Air and water are forced into cracks at high
  pressure

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Coastal Erosion (Crashing Surf)
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Crashing Surf, Oregon Coast
Source Criag Tuttle/The Stock Market
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Coastal Erosion
Source Paul Sequeira/Photo Researchers, Inc.
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Lighthouse at Morris Island, SC
Source Donald Carter
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Coastal Erosion Structures

• Headlands- cliffs that jut seaward
• Wave-cut bench is produced when waves undercut
  headland
• Sea Caves are produced when waves are refracted
  against the side of headland
• Sea Arch forms when two Sea Caves erode
  completely through the headland
• Sea Stack is formed when Sea Arches collapse

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Erosional Coastal Landforms
Submerged Shallow Area Bends Waves
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Erosional Coastal Landforms
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Sea Caves on Cape Kildare, Prince Edward Island,
Canada
Source John Elk/Bruce Coleman
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Deposition of A Tombolo
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A Tombolo Landward of A Sea Stack Big Sur,
California
Source Cliff Wassmann
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Coastal Protection

• Riprap/Seawall- protects shore lines
• Groins Stabilize beaches
• Jettys Keep inlets clear

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Beach-Protection Structures - Riprap
Source Jack Dermid /Photo Researchers, Inc.
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Beach-Protection Structures Seawall Along the
Gulf Coast of Louisiana
Source Martin Miller
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Groins
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Jetties
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Groins off Cape May, New Jersey
Source John S. Shelton
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Jetty in Miami Beach, Florida
Note how it is much narrower than the original
inlet. Smaller cross-sectional area therefore
higher velocity, more erosion in the new channel,
keeps the channel deep.
Source Townsend P. Dickinson
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Transport and Depositional Features

• A beach is a narrow segment of coast washed by
  waves/tides and covered with sediments
• Foreshore is the area between low tide and high
  tide
• Backshore is the area between high tide and sea
  cliff or inland vegetation line
• Beach face is the steepest part of Foreshore
• Berm is a horizontal bench of storm sediment

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Components of A Typical Beach
How to tell a berm from a sand dune
Small notes for Prof. Smart to repeat previous
slides Beach a narrow strip of land washed by
waves or tides Foreshore is the area between low
tide and high tide Backshore is the area between
high tide and sea cliff or inland vegetation
line Beach face is the steepest part of
Foreshore Berm is a horizontal bench of storm
sediment
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Volcanic Black Sand Beach
Detrital sediments are classified with particle
sizes. Sand is a size, not one specific mineral
Source Breck P. Kent
Beach sediments usually quartz, but sometimes
mafic minerals
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Transport and Depositional Features

• Longshore Drift causes deposits
• Spit is a finger-like ridge of sand deposited
  where Longshore drift encounters deeper water
• Hook is a curved spit
• Baymouth is a spit that covers the access to a
  bay the area behind it fills with sediment

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Deposition Spits, Hooks, and Baymouth Bars
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Filling of Tidal Inlets
Cheesequake Park
Shawangunk Formation
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A Spit at Cape Henlopen, Delaware
Source Cliff Wassmann
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Baymouth Bars on Marthas Vineyard, MA
Source John S. Shelton
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Sea Level Change

• 1. Glaciers
• Glaciers lower sea-level slowly
• They melt quickly sea level rises
• 2. Mid Ocean Ridges (MORs)
• Mid Ocean Ridge raises sea level if large
• and active
• Lowers sea level if activity slows - becomes
  smaller
• Sit in the bath tub water level rises

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Coast Types I Primary Coasts Mostly Non-Marine

• Coast types formed mainly from non-marine
  processes such as glaciation (Long Island) ,
  stream deposition (deltas) , fluctuating sea
  levels
• Also Organic Coasts - reefs, mangroves

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Nonmarine Processes - Fjords
Glacial Erosion and Glacial Melting - Sea Level
Rise
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Nonmarine Processes glacial meltingSea Level
Rises
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Nonmarine Processes - Rebound
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Nonmarine Processes - Uplift
Convergent Margins
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Nonmarine Processes - Deltas
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Combined changes to coastlines

• Tectonic uplift and sea-level changes
• Postglacial Isostatic rebound and sea-level
  changes
• Mid-ocean Ridge grows/wanes and sea-level changes

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Sea-level rise exceeds uplift -Transgression
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Sea-level rise exceeds rebound
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Volcanism exceeds sea-level rise
Coastline is less flooded.
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Organic Coasts

• Fringing Reef- initially surround land, grow
  seaward
• Barrier Reef- separated from coast by a lagoon
• Atoll- circular structure from great depth that
  encloses shallow lagoon
• Mangroves

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Biological Processes Coral Reefs
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Evolution of Carbonate Reefs
Charles Darwin
coral larvae are planktonic
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Great Barrier Reef, Australia
Source David Ball/The Stock Market
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Wake Island, a Coral Atoll
Source William E. Ferguson
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Biological Processes - Mangroves
Make you own island
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Typical Mangrove Coast, Florida Everglades
Source S. J. Krasemann/Peter Arnold, Inc.
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Coast Types II Secondary Coasts Marine
Processes

• Ongoing marine erosion and deposition
• Erosion Headlands, wave cut terraces, sea caves,
  stacks, and arches
• Deposition Beaches, spits, hooks, tombolos
• Barrier Islands are nearly continuous ridges of
  sand parallel to main coast

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Barrier Island and Lagoon, nr.Cape Hatteras
Source Breck P. Kent
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Inlet Created by Hurricane Waves (North Carolina)
Source Associated Press/Raleigh News Observer,
Chris Seward
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Migration of Barrier Islands
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Migration of Barrier Islands (contd)
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Migration of Barrier Islands (contd)
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Plate Tectonic Impacts

• Divergent/Convergent plate boundaries possess
  steep continental shelves
• Passive Continental Margins- have broad
  continental shelves and have beaches with spit
• Island Arcs can protect coastlines
• Allows deltas to form

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West Coast Shorelines- Active Margin
Source William Boyce/Corbis
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East Coast Shorelines Passive Margin
Source Peter Kresan
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Island Arcs protect coastlineallow deltas to
form
Thailand
Cambodia
Laos
(Chao Phraya River)
Delta Protected from Typhoons and Tsunamis
Sumatra, Indonesia
Source Tom Van Sant / Geoshere Project Santa
Monica/Science Photo Library
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As long as we are here
Draw a cross section Sunda to Sumatra, trench,
AW, FAB, Arc, BAB, microcontinent
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Back to coastlineshuman impacts on coastline

• Break waters, groins, and jetties all cause
  deposition of sediment somewhere
• Other areas lose beach sand
• Development destroys vital shoreline vegetation
• Water and petroleum pumping cause subsidence

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Our efforts to control nature can be a expensive
struggleSanta Barbara Harbor in 1931
Source Fairchild air photos 0-139 E-5780,
UCLA Department of Geography Aerial Photo Archives
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Santa Barbara Harbor in 1977
Source John S. Shelton
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North Carolina's Outer Banks
Humans remove any new sand piled up on their
property. Normal bar migrations thwarted and
barrier narrows.
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Erosion at Lake Michigan
1. Glacial Till easily eroded 2. Long Reach for
winter storm waves 3. Reduced ice recently no
protection 4. Excess Precipitation High Lake
Levels
Source Michael J. Chrzastowski, Illinois State
Geological Survey
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Subsidence of the Galveston, TX
Geo-humor
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End of Chapter 17Shores and Coastal
ProcessesNext time is Ch. 19, then review