Chapter20 coastal processes

Chapter 20: Coastal Processes and Landforms Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack

Coastal Processes and Landforms
Large percentage of world’s population lives near the coast

20.1 The Coastal Zone
Shoreline
Sea Level
Average position of shoreline
Coastal zone
Nearshore zone
Breaker zone
Surf zone
Swash zone (backwash)
Offshore zone

20.2 Origin and Nature of Waves
Waves
Wave crests
Wave troughs
Wave height
Wavelength
Wave steepness
Wave period
Tides
Tsunamis
Wind waves

Tides
Gravitational pull of the moon and sun is the force that causes tides
Moon has a stronger pull
Centrifugal force
Tidal range
Difference in sea level between high and low tide

Spring tide
Neap tide
Q: How many spring tides and neap tides occur each month?

Tides
Semidiurnal tide
Diurnal tide
Mixed tide
Q: What is the tidal pattern on the coastal area nearest where you live?

Tidal range varies due to:
Shape of coastline
Water depth
Access to open ocean
Submarine topography
Largest tidal range (Bay of Fundy, Canada)

Tsunamis
Long-wavelength waves that form when a large mass of water displaced upward of downward by:
Earthquakes
Volcanic eruptions
Landslide
December, 2004 Indonesia earthquake and tsunami

Wind Waves
Most waves on surface of standing body of water created by wind
Frictional drag and pressures cause irregularities in the water surface
Waves can travel thousands of miles
3 Factors determine height of wind waves
Wind velocity
Duration of wind
Fetch

Waves are traveling forms
Deep-water
Wave base

Why don’t the waves break in deeper water?

20.3 Breaking Waves
Rip currents
Relatively narrow zones of strong, offshore-flowing water
Q: Why are these currents a hazard to swimmers?

20.4 Wave refraction and Littoral drifting
Wave refraction
Bending of a wave in map view as it approaches a shoreline
Q: How will this coastline change over a long period of time?

Wave refraction
Coastlines tend to straighten over time
Q: What happens to sediment eroded from the headlands?

Not all waves refract completely before they break
Littoral drifting
Incomplete refraction produces sediment transport in the coastal zone

When a wave crest approaches a straight, gently sloping shoreline at a large angle, it interacts with the bottom and starts to slow down
Beach drifting
Longshore current
Longshore drifting

20.5 Coastal Erosion
Key Terms
Corrosion
Hydraulic action
Abrasion
Coastal Erosional Landforms
Coasts of high relief are dominated by erosion
Sea cliffs (or lake cliffs)

Notch
Cobble beach
Sea caves

Sea arches
Sea stack

Abrasion platform
Marine terraces

20.6 Coastal Deposition
Coastal Deposition
Sediments accumulate where wave energy is low
3 principal sources of coastal sediment:
Streams
Delta
Estuary
Coastal cliff erosion
Offshore sources

Coastal Depositional Landforms
Beach
Most common form
Wave-deposited feature
Sandy beach
Cobble beach

Middle latitudes beaches are generally narrower, steeper and composed of coarser material in winter compared to summer
Longshore bar

Spits
Tombolo

Barrier beaches
Lagoons
Barrier spit
Barrier islands

Barrier Islands
Locations: Atlantic (Cape Hatteras) and gulf coasts
Change drastically with severe storms

Beach systems
Equilibrium when input and output of sediment are equal
Groin
Human made obstruction of longshore current (increases size of some beaches)

20.7 Types of Coasts
Coastal Classification is based on plate tectonics
Passive-margin
Low relief and broad coastal plain
Continental shelves
e.g. East Coast
Active-margin

Coastal Classification
Active-margin
High relief and narrow coastal plain
e.g. West Coast of U.S. along Pacific Ocean

Regional scale
Coastlines of emergence
Water level has fallen or the land has risen
Best developed along active-margin coasts (e.g. west coast of U.S)

Regional scale
Coastlines of submergence
Many features of the former shore are present
2 types of submerged coastlines
Rias coasts
Fjord coasts

Fjord coasts
Highly irregular
Deep, steep sided arms
Locations: Norway, Alaska, Chile, and Canada

Another Regional classification system of coasts
Primary coastline
Erosion and deposition dominant
Result from rapid changes in coastline
Secondary coastline
Formed by waves and aquatic organisms

20.8 Islands and Coral Reefs
Three basic ocean types of islands
Continental
Geologically apart of continent
Examples: Greenland, Great Britain, New Guinea, and Borneo
Oceanic
Atolls

Oceanic
Volcanoes that rise from deep ocean floor
Along trenches: Aleutians, Tonga, Marianas
Along mid-ocean ridges: Iceland, Azores
Along chains: Hawaiian islands

Atoll
Island consisting of a ring of coral reefs
Grown up from a subsiding volcanic island
Encircle a central lagoon

Coral Reefs
Shallow, wave-resistant structures
Remains of tiny sea animals (skeleton of calcium carbonate)
Types of Reefs
Fringing reef
Barrier reef
Challenge for human habitation

Physical Geography End of Chapter 20: Coastal Processes and Landforms

Chapter20 coastal processes

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