Coastlines

• Zones
– Coastal Regions
• Marine influence
– Shore
• Wave influence
– Beach
• Sediment accumulation

Coastal Geomorphology
• Primary Influences
– Margin Type - active versus passive
– Sediment Supply
– Climate
– Relative Sea Level History
• Eustasy versus subsidence
– Ocean processes

Coastlines
• Types
• Primary Coasts
– Terrestrial erosion and S/L rise
– Terrestrial deposition
– Tectonism

Primary Coasts
• Terrestrial erosion and relative S/L rise
– Submerged glaciated coasts - fjords
– Submerged river valleys

Primary Coasts
• Terrestrial deposition
– Dune Coasts
– Delta
• velocity decreases as stream enters ocean

Delta
• Deposition => distributary channels
• Delta Growth => channel migration
Delta
• depositional features = 1) Prodelta, 2) Delta front, 3) Delta plain
• Progradation
Delta Types
• deltas shaped by fluvial processes plus tides and waves
– River dominated
– Wave dominated
– Tide dominated

Primary Coasts
• Tectonic Coasts
– Fault Coasts
– Volcanic Coasts

Coastlines
• Types
• Secondary Coasts
– Marine erosion
– Marine deposition
– Organic

Secondary Coasts
• Marine erosion
– Begin as primary
– Sea arches, stacks & tombolos

Secondary Coasts
• Marine deposition
• Emergent/depositional coastlines
• Barrier islands
– S/L change
– storms

Secondary Coasts
• Organic
– Mangroves
– Reefs

Beaches
• Beaches are the most prevalent natural feature of the coastal zone
• Mud, sand, cobbles, boulders

Beaches
• Parts
• Offshore zone- before waves break
• Foreshore Zone,
– Breaker zone
– surf zone
– swash zone
• Backshore zone- beyond mean high tide

Beaches
• Beach modifying processes
– Waves
– Tides & Currents
• Beach change =
– Balance between sediment supply, accumulation, & transport
Waves on beaches
• Surf
• Swash and backwash
• Waves approaching at oblique angles
– Longshore currents
– Sediment transport
Waves on beaches
• places where 2 longshore currents converge =
– rip current, or rip tides
– Rapid, narrow currents moving offshore
Beaches - seasonal changes
• Summer = gradual sediment accumulation
• Winter = rapid sediment erosion
– Offshore bars
Beach Sediment
• So, where does sand come from?
• River supply (most sand is created by the action of rivers flowing to the sea)
• Cliff erosion
• Onshore transport from the offshore sea bottom.
• Longshore currents
Beach Sediment
• Composition - depends on source
• Continental - lithics & quartz
• Tropical - carbonates
• Volcanic - black or green sands
Beach Sediment
• Carbonate beaches
– Rapid lithification
– Beach rock

Beaches - Sediment Balance
• Sediment accumulation
• Sediment loss
– off-shore transport - trapped in shallow submarine canyons
– wind transport forming dunes
– by longshore currents
• Net erosion, net deposition, equilibrium

Beach Dynamics - human intervention
• Equilibrium = rare
• Beaches = desirable places to live = problem
• Jetties, groins, and sea walls

Estuaries
• Drowned coastal valleys
• fresh water and seawater mix
• Influenced by salt water and tides
• How do they form?
• a rise in sea level

Estuaries
• How does water circulate in an estuary?
• There are three main types of estuaries in regard to circulation patterns.
• There are:
• 1. salt-wedge estuaries
• 2. partially mixed estuaries
• 3. well-mixed estuaries.

Estuaries
• Salt-wedge estuaries
• narrow relative to their water depth
• dominated by fresh water (river discharge)
• There are relatively weak tidal currents
• There is a sharp halocline

Estuaries
• Well-mixed estuary.
• tidal processes dominate.
• The top and bottom waters mixed - turbulence.
• wide areas- separation of water comes = Coriolis effect.
• marine sediments imported
– right hand side of the estuary (in N. Hemisphere)
• River contributions - left side of the system.

Estuaries
• Partially mixed estuaries
• tidal currents = stronger
• less sharp halocline
• 2 layered circulation
• These create turbulence that mixes the water.
• sediments coming into the estuary from the continental shelf.
• area close to the ocean tends to have marine sediments,nearer to the rivers- more river sediments.
deposition of a sand bar at the estuary mouth where the cu