Shores and Coastal Processes. Shorelines are places where bodies of water meet dry land Coasts are...
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Transcript of Shores and Coastal Processes. Shorelines are places where bodies of water meet dry land Coasts are...
Shores and Coastal ProcessesShores 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
Parts of A WaveParts of A WaveWaves are caused by _____________?
Fetch – Southern Ocean, Straits of Magellan
Oscillatory and Translatory MotionOscillatory and Translatory Motion
Translatory motion re-suspends sediment
Shores and Coastal ProcessesShores 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.
Rip CurrentsRip Currents
Sand Bar
Cut in Bar
Sand bars are big ripplesstorms cut them, causing arip channel
Tides – Mostly the MoonTides – 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
Large Tidal ExtremesLarge 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.
The Effect of Tides On Shorelines The Effect of Tides On Shorelines – – River Hebert in Nova ScotiaRiver Hebert in Nova Scotia
Source: Clyde H. Smith/Peter Arnold, Inc.
Tidal BoreAnecdote: local tidal bore
Coastal Erosional FeaturesCoastal 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
Coastal Erosion StructuresCoastal 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
Sea Caves on Cape Kildare, Prince Edward Island, CanadaSea Caves on Cape Kildare, Prince Edward Island, Canada
Source: John Elk/Bruce Coleman
A Tombolo Landward of A Sea Stack A Tombolo Landward of A Sea Stack – – Big Sur, Big Sur, CaliforniaCalifornia
Source: Cliff Wassmann
Coastal ProtectionCoastal Protection
• Riprap/Seawall- protect shore lines
• Groin – stabilizes beaches
• Jetty – keep inlets clear
• Breakwater – protect a harbor
Beach-Protection Structures Beach-Protection Structures - - Riprap Riprap
Source: Jack Dermid /Photo Researchers, Inc.
Beach-Protection Structures Beach-Protection Structures ––Seawall Along the Gulf Coast of LouisianaSeawall Along the Gulf Coast of Louisiana
Source: Martin Miller
Jetty in Miami Beach, FloridaJetty in Miami Beach, Florida
Source: Townsend P. Dickinson
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.
Components of A Typical BeachComponents of A Typical Beach
Small notes for Prof. Smart to repeat previous slides:Beach a narrow strip of land washed by waves or tidesForeshore is the area between low tide and high tideBackshore is the area between high tide and sea cliff or inland vegetation lineBeach face is the steepest part of ForeshoreBerm is a horizontal bench of storm sediment
How to tell a berm from a sand dune
Volcanic Black Sand BeachVolcanic Black Sand Beach
Source: Breck P. Kent
Beach sediments usually quartz, but sometimes mafic minerals
Detrital sediments are classified with particle sizes. Sand is a size, not one specific mineral
Transport and Depositional Transport and Depositional FeaturesFeatures
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
Baymouth Bars on Martha’s Vineyard, MABaymouth Bars on Martha’s Vineyard, MA
Source: John S. Shelton
Sea Level ChangeSea Level Change1. Glaciers• Glaciers lower sea-level slowly• They melt quickly – sea level rises
2. Mid Ocean Ridges (MOR’s)• 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
Coast Types I Coast Types I Primary Coasts – Mostly Non-MarinePrimary 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
Combined changes to coastlinesCombined 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
Organic CoastsOrganic 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
Typical Mangrove Coast, Florida Typical Mangrove Coast, Florida EvergladesEverglades
Source: S. J. Krasemann/Peter Arnold, Inc.
Coast Types II – Secondary Coasts Coast Types II – Secondary Coasts
Marine ProcessesMarine ProcessesOngoing marine erosion and depositionErosion: Headlands, wave cut terraces,
sea caves, stacks, and archesDeposition: Beaches, spits, hooks,
tombolos
• Barrier Islands are nearly continuous ridges of sand parallel to main coast
Barrier Island and Lagoon, nr.Cape HatterasBarrier Island and Lagoon, nr.Cape Hatteras
Source: Breck P. Kent
Inlet Created by Hurricane Waves Inlet Created by Hurricane Waves (North Carolina)(North Carolina)
Source: Associated Press/Raleigh News & Observer, Chris Seward
Plate Tectonic ImpactsPlate 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
West Coast ShorelinesWest Coast Shorelines- Active Margin- Active Margin
Source: William Boyce/Corbis
Island Arcs protect coastlineIsland Arcs protect coastlineallow deltas to formallow deltas to form
Source: Tom Van Sant / Geoshere Project Santa Monica/Science Photo Library
Thailand CambodiaLaos
(Chao Phraya River)
Sumatra, Indonesia
Delta Protected from Typhoons and Tsunamis
As long as we are hereAs long as we are here
Draw a cross section Sunda to Sumatra, trench, AW, FAB, Arc, BAB, microcontinent
Back to coastlinesBack to coastlineshuman impacts on coastlinehuman 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
Our efforts to control nature can be a expensive struggleOur efforts to control nature can be a expensive struggle
Santa Barbara Harbor in 1931Santa Barbara Harbor in 1931
Source: Fairchild air photos 0-139 & E-5780, UCLA Department of Geography Aerial Photo Archives
North Carolina's Outer BanksNorth Carolina's Outer Banks
Humans remove any new sand piled up on their property. Normal bar migrations thwarted and barrier narrows.
Erosion at Lake MichiganErosion at Lake Michigan
Source: Michael J. Chrzastowski, Illinois State Geological Survey
1. Glacial Till easily eroded 2. Long Reach for winter storm waves3. Reduced ice recently – no protection 4. Excess Precipitation – High Lake Levels