Chapter 20: Coastal Processes and Landforms Physical Physical Geography Geography Ninth Edition Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso
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
20.2 Origin and Nature of 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
20.2 Origin and Nature of Waves
• Spring tide• Neap tide
Q: How many spring tides and neap tides occur each month?
20.2 Origin and Nature of Waves
• Tides– Semidiurnal tide– Diurnal tide– Mixed tide
Q: What is the tidal pattern on the coastal area nearest where you live?
20.2 Origin and Nature of Waves
• Tidal range varies due to:– Shape of coastline– Water depth– Access to open ocean– Submarine topography
• Largest tidal range (Bay of Fundy, Canada)
20.2 Origin and Nature of Waves
• 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
20.2 Origin and Nature of Waves
• 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
20.2 Origin and Nature of Waves
• Waves are traveling forms
• Deep-water
• Wave base
20.2 Origin and Nature of Waves
• 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?
20.4 Wave refraction and Littoral drifting
• Wave refraction– Coastlines tend to
straighten over time
Q: What happens to sediment eroded from the headlands?
20.4 Wave refraction and Littoral drifting
• Not all waves refract completely before they break
• Littoral drifting– Incomplete
refraction produces sediment transport in the coastal zone
20.4 Wave refraction and Littoral drifting
• 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)
20.5 Coastal Erosion
• Coastal Erosional Landforms– Notch– Cobble beach– Sea caves
20.5 Coastal Erosion
• Coastal Erosional Landforms– Sea arches– Sea stack
20.5 Coastal Erosion
• 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
20.6 Coastal Deposition
• Coastal Depositional Landforms– Beach
• Most common form• Wave-deposited
feature• Sandy beach• Cobble beach
20.6 Coastal Deposition
• Coastal Depositional Landforms– Middle latitudes beaches are generally narrower,
steeper and composed of coarser material in winter compared to summer
– Longshore bar
20.6 Coastal Deposition
• Coastal Depositional Landforms– Spits– Tombolo
20.6 Coastal Deposition
• Coastal Depositional Landforms– Barrier beaches– Lagoons– Barrier spit– Barrier islands
20.6 Coastal Deposition
• Coastal Depositional Landforms– Barrier Islands
• Locations: Atlantic (Cape Hatteras) and gulf coasts
• Change drastically with severe storms
20.6 Coastal Deposition
• 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
20.7 Types of Coasts
• Coastal ClassificationActive-margin
• High relief and narrow coastal plain
• e.g. West Coast of U.S. along Pacific Ocean
20.7 Types of Coasts
• 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)
20.7 Types of Coasts
• Coastal Classification– Regional scale– Coastlines of
submergence• Many features of the
former shore are present
– 2 types of submerged coastlines
• Rias coasts• Fjord coasts
20.7 Types of Coasts
• Fjord coasts– Highly irregular– Deep, steep sided arms– Locations: Norway,
Alaska, Chile, and Canada
20.7 Types of Coasts
• 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
20.8 Islands and Coral Reefs
• Oceanic– Volcanoes that rise from deep ocean floor– Along trenches: Aleutians, Tonga, Marianas– Along mid-ocean ridges: Iceland, Azores– Along chains: Hawaiian islands
20.8 Islands and Coral Reefs
• Atoll– Island consisting of
a ring of coral reefs– Grown up from a
subsiding volcanic island
– Encircle a central lagoon
20.8 Islands and Coral Reefs
• 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