Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor
COASTAL LANDFORMS STUDY GUIDE
Assigned reading: Elemental Geosystems, Christopherson, Chapter 13, Pages 429-459
Web Learning Module: Coastal Landforms
- Many factors combine to create the variety of coastal landscapes.
These factors include: erosion, transport, and deposition by waves, tides,
currents, the landscape adjoining the coast, relative changes of sea and
land, the influence of people’s engineering works, and special effects
such as coral, volcanoes, ice, and deltas.
- Waves are the force that shapes the coastline. Wind blowing
over the surface of the ocean forms waves which transfer some of the wind's
energy to the coastline. Orbital water motion extends to a depth
of half a wavelength.
- When a wave reaches shallow water, friction with the bottom flattens
the wave orbits and causes the wave to slow down and peak up forming a
crest. Eventually the crest collapses forward onto the beach.
- Waves that approach the coast at an angle cause beach drifting (swash
and backwash) and longshore currents in the surf zone. Longshore
transport and progradation (forward building) create a variety of depositional
features such as spits, baymouth bars, and beaches. Drifting sand
may be deposited inside breakwaters or against jetties or groins.
- Local erosion may supply some sediment but rivers supply most of
the sand for beaches. If the rivers are dammed, the sand supply is cut
off and beaches become narrower. Coastal property is threatened by
wave erosion when beaches are narrow.
- Waves erode landscapes by hydraulic action, abrasion, solution,
and attrition. Slow (5-8 per minute) spilling waves build up the
beach in calm weather. Faster (13-15 per minute) plunging waves erode
the beach during storms.
- The most common coastal landscapes are cliffed coastlines of headlands
and bays and barrier island coasts. Most of the cliffed coastlines
were formed due to submergence by rising sea level. Former river
valleys drowned by the sea form ria coasts, drowned glacial valleys form
- Over time, coastlines of headlands and bays are straightened by
erosion of headlands and deposition in the bays. Wave refraction
concentrates wave energy on the headlands and disperses it in bays.
- As waves erode the softer rock in cliffs, they form caves and arches.
Stacks and stumps form when arches collapse. As the cliffs erode
backward, they leave a wave-cut abrasion platform at the base. In
deeper water, a wave-built depositional terrace forms.
- Barrier island coasts develop where there is a gentle offshore
gradient, slight tidal range, and a low-lying landscape bordering the coast.
This is the most common coastline in the Eastern and Southern United States. Submarine bars that form parallel to the coastline grow into barrier islands which are gradually driven landward by wind and waves.
- A rise of land relative to the sea produces wave-cut marine terraces.
- Coral coasts form from biological organisms growing in warm, clear
water. Coral may take the form of fringing reefs, barrier reefs, or atolls.
- Describe the factors that combine to create the variety of coastal
- Explain how waves form.
- What happens to waves when they reach the shoreline?
- Describe longshore transport. Draw a diagram to show how sand
moves along a beach face when the waves approach a beach at an angle. Describe how longshore drift forms spits and baymouth bars. How can longshore drift be stopped or altered by people’s activities?
- What is the source of sand for beaches? What would happen
to beaches if all the rivers were dammed?
- Explain how waves erode. How do summer beaches differ from
- What are the most common coastal landscapes? How do they differ?
- Describe how waves can straighten an irregular coastline of headlands
- Describe how waves affect coastlines with varying resistance to
erosion to produce cliffs, caves, arches, stacks, and wave-cut abrasion
- Describe the development of a barrier island coast.
- Draw a diagram to show the formation of a marine terrace by a rise
of land relative to the sea.
- Describe the circumstances in which coral may form.
Go To Top Of Page
Return to Coastal Landforms Learning Module
Go to Physical Geography
Course Content and Learning Modules
Created by Rita D. Haberlin, Geography Professor
Peralta Community College District
333 East Eighth Street
Oakland, CA 94606
This Geography Site Is Maintained By Patricia A. Kulda
Last Update August 20, 2010