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Chapter 20: Coastal Processes and Landforms

Physical Physical GeographyGeographyNinth EditionNinth 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)


• Coastal Erosional Landforms– Notch– Cobble beach– Sea caves


• Coastal Erosional Landforms– Sea arches– Sea stack


• Coastal Erosional Landforms– 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


• Coastal Depositional Landforms– Middle latitudes beaches are generally narrower,

steeper and composed of coarser material in winter compared to summer

– Longshore bar


• Coastal Depositional Landforms– Spits– Tombolo


• Coastal Depositional Landforms– Barrier beaches– Lagoons– Barrier spit– Barrier islands


• Coastal Depositional Landforms– Barrier Islands

• Locations: Atlantic (Cape Hatteras) and gulf coasts

• Change drastically with severe storms


• Coastal Depositional Landforms– 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 tectonics1. Passive-margin

• Low relief and broad coastal plain

• Continental shelves• e.g. East Coast

2. Active-margin


• Coastal ClassificationActive-margin

• High relief and narrow coastal plain

• e.g. West Coast of U.S. along Pacific Ocean


• Coastal Classification– 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)


• Coastal Classification– 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 islands1. Continental

• Geologically apart of continent• Examples: Greenland, Great Britain, New Guinea,

and Borneo

2. Oceanic

3. 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

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Education

coastal processes

coastal area nearest

nature of waves wind

wavelength waves

waves break

nature of waves tsunamis

water surface waves

nature of waves tidal