Shores and Coastal Processes
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
Typical Coast
Waves are caused by _____________?
Parts of A Wave
Fetch – Southern Ocean, Straits of Magellan
Oscillatory and Translatory Motion
Translatory motion re-suspends sediment
Wave Refraction
Still a small ‘longshore component
backwash
swash
Kids at the beach
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.
Longshore Currents (Swash and
Backwash)
Rip Currents
Cut in Bar
Sand Bar
Sand bars are big ripples
storms cut them, causing a
rip channel
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
Tidal Bulges
Affect of the Sun Much less
The Effect of Tides On Shorelines
Tides mostly caused by the Moon
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.
The Effect of Tides On Shorelines –
River Hebert in Nova Scotia
Tidal Bore
Anecdote: local tidal bore
Source: Clyde H. Smith/Peter Arnold, Inc.
Low Tide at Bay of Fundy
Source: William E. Ferguson
Rising Tide at Bay of Fundy
Maximum
Source: William E. Ferguson
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
Coastal Erosion (Crashing Surf)
Crashing Surf, Oregon Coast
Source: Criag Tuttle/The Stock Market
Coastal Erosion
Source: Paul Sequeira/Photo Researchers, Inc.
Lighthouse at Morris Island, SC
Source: Donald Carter
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
Erosional Coastal Landforms
Submerged Shallow
Area Bends Waves
Erosional Coastal Landforms
Sea Caves on Cape Kildare, Prince Edward Island, Canada
Source: John Elk/Bruce Coleman
Deposition of A Tombolo
A Tombolo Landward of A Sea Stack – Big Sur,
California
Source: Cliff Wassmann
Coastal Protection
• Riprap/Seawall- protect shore lines
• Groin – stabilizes beaches
• Jetty – keep inlets clear
• Breakwater – protect a harbor
Beach-Protection Structures - Riprap
Source: Jack Dermid /Photo Researchers, Inc.
Beach-Protection Structures –
Seawall Along the Gulf Coast of Louisiana
Source: Martin Miller
Groins
Groins off Cape May, New Jersey
Source: John S. Shelton
Jetties
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
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
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
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
Deposition Spits, Hooks, and Baymouth
Bars
Filling of Tidal Inlets
Cheesequake Park
Shawangunk Formation
A Spit at Cape Henlopen, Delaware
Source: Cliff Wassmann
Baymouth Bars on Martha’s Vineyard, MA
Source: John S. Shelton
Sea Level Change
1. 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
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
Combined changes to coastlines
• Tectonic uplift and sea-level changes
• Postglacial Isostatic rebound and sea-level
changes
• Mid-ocean Ridge grows/wanes and sealevel changes
Sea-level rise exceeds uplift -Transgression
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
Evolution of Carbonate Reefs
Charles Darwin
coral larvae are planktonic
Wake Island, a Coral Atoll
Source: William E. Ferguson
Biological Processes - Mangroves
“Make you own island”
Typical Mangrove Coast, Florida
Everglades
Source: S. J. Krasemann/Peter Arnold, Inc.
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
Barrier Island and Lagoon, nr.Cape Hatteras
Source: Breck P. Kent
Inlet Created by Hurricane Waves
(North Carolina)
Source: Associated Press/Raleigh News & Observer, Chris
Seward
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
West Coast Shorelines
- Active Margin
Source: William Boyce/Corbis
East Coast Shorelines – Passive Margin
Source: Peter Kresan
Thailand
Island Arcs protect coastline
allow deltas to form
Cambodia
Laos
(Chao Phraya River)
Delta Protected from
Typhoons and Tsunamis
Sumatra,
Indonesia
Source: Tom Van Sant / Geoshere Project
Santa Monica/Science Photo Library
As long as we are here
Draw a cross section Sunda to Sumatra, trench, AW, FAB, Arc, BAB, microcontinent
Back to coastlines
human 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 struggle
Santa Barbara Harbor in 1931
Source: Fairchild air photos 0-139 & E-5780, UCLA Department of Geography Aerial Photo Archives
Santa Barbara Harbor in 1977
Source: John S. Shelton
North Carolina's Outer Banks
Humans remove any new
sand piled up on their
property. Normal bar
migrations thwarted and
barrier narrows.
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
Subsidence of the Galveston, TX
Geo-humor
End of
Shores and Coastal Processes