1. Coastal Processes and Landforms
Landform Geography
Coastal Processes and Landforms

2. Coastal Processes and Landforms
Oceans and Seas
Nature of Coastlines: Intersection of Earth’s Spheres
Coastal Landforms
Human Impacts on Coastlines

3. Oceans and Seas
Oceans – largest bodies of water: Pacific, Atlantic, Indian, Southern, and Arctic
Seas – next largest water bodies: Black, Mediterranean, Barents, etc.
Gulf – next largest, usu. opens to larger water body: Mexico, Alaska, Guinea, etc.
Bay – smaller still: Fundy, Biscay, etc.

4. Oceans and Seas

5. Water as Solvent
Salinity – concentration of dissolved solids in seawater – global seawater salinity parts per thousand (‰)
Brine – water with >35‰ salinity
Brackish water - <35‰ salinity

6. Shaping the Coastline Key to shaping coastline is movement of water
Eustatic Change - changes in water level in ocean – due to tectonic uplift or hydro cycle variation
Land above sea level forms river valleys that extend to sea level – when sea level rises, valley floods, as with Chesapeake Bay or Delaware Bay
Ria – river valley flooded by rising sea level
Fjord – glacial valley flooded by rising sea level

7. Eustatic Sea Level Changes

8. North American Coastline Through Time
Lowest sea levels occurred during glaciations when water was tied up in glaciers (130k & 19k bp) – highest sea levels in interglacial periods (120k bp)

9. Tides
Regular, predictable oscillations of sea level – due to gravitation of moon (56%) & Sun (44%)
High tide on side of Earth facing moon and on side away from moon – ellipsoid shape
Long, narrow bays usually have highest tides – up to 16 meters in Bay of Fundy in eastern Canada

11. Waves
Oscillations in water due to force of friction from wind blowing across its surface
Waves travel horizontally, but most movement of water is vertical, up-and-down
Near coast seafloor slopes upward – wave base intersects ocean floor – wave pushes water up as it slows – waves pile up from behind - wave height exceeds 7X wavelength, and forms a breaker
Only horizontal movement of water from breaker to beach, called surf – erosional agent

12. Wave Compression

13. Tsunami
Caused by undersea earthquakes with vertical displacement, volcanic eruptions, or landslides
Vertical displacement of water causes fast wave with long wavelength – no harm at sea, but massive as it hits coastline
March 2011– Pacific plate subducts under North American plate which snaps upward – massive tsunami hits Indian Ocean

14. 2011 Japan Earthquake

15. Littoral Processes Transport & deposition of sediment in shore zone
Longshore current – forms when wave hits beach at oblique angle – water deflects downwind, parallel to beach
Longshore drift – process of longshore current eroding & carrying sediment down shore
Beach drift – zig-zag motion of sediment down beach due to swash & backwash
Littoral Drift – longshore & beach drift together

16. Littoral Drift

17. Coastal Landforms Erosional Coastlines
Breaking waves have great power to erode
Headland – promontory that juts into ocean or sea – made of resistant rock
Waves slow & pivot around headlands – erosive power of waves concentrated on headland
Retrogradation – retreat of coastline due to erosion
Wave-Cut Bluff – basic erosional landform of coastlines – near-vertical cliff at water’s edge

18. Coastal Erosional Landforms

19. Depositional Coastlines
Progradation – process of coastline extending outward into water through deposition
Beach – dynamic transition from sea to land
Offshore – under water, where waves break
Foreshore – rise & fall of tides
Offshore Bar – between offshore & foreshore
Beach Ridge – at high water line
Backshore – flat, only covered in storms

20. Beach Cross Section

21. Spits and Baymouth Bars
Longshore current carries sediment down beach
Current slows upon reaching bay – sand deposited as a Spit extending out into bay – current in bay turns spit toward land in hook shape
Baymouth Bar – spit extends across bay, isolating it from ocean – bay now called Lagoon
Tombolo – longshore currents from 2 directions meet – sand extends out to island or sea stack

22. Depositional Landforms

23. Barrier Islands Elongated bars of sand that form parallel to shore
Likely formed from sand deposited on cont. shelf during last glaciation – waves & wind shaped sand
Lagoons w/mudflats form behind barrier islands
Mudflats develop into vegetated salt marsh

24. Coral Reefs
Coral polyps excrete external skeletons of calcium carbonate (limestone) – Coral Reefs
New reefs form on top of old, dead reefs
30º N - 25º S latitude, water warmer than 20º C
3 settings:
Fringing reef – on shallows around island
Barrier reef – line of coral parallel to shore
Atoll – semicircular reef around degraded volcanic island

25. Development of Atoll

26. Global Distribution of Coral Reefs

27. Human Impacts on Coastlines
37% of world pop. live <60 mi. from shore (2 billion) – 50% within 120 miles of shore
In US, 53% of pop. live near coastline
Coastal Engineering Purposes:
Protecting shore & property from hazards
Stabilizing & nourishing beaches
Maintaining traffic & trade into ports

28. Mitigating Coastal Hazards
Raise buildings on stilts so waves roll underneath
Sea wall – vertical, concrete wall to absorb energy of waves
Revetment – slope covered with large rocks (rip-rap) to absorb energy of waves
These work locally, but they aggravate erosion up and down shore from wall due to wave refraction

29. Beach Nourishment
Bringing sand to beaches that have eroded – over $336M spent in Florida since 1960s
How?
Trucking in sand from remote location
Limit loss of sand through groins – low walls built at right angles to beach – intercept longshore drift
Jetties – stone or concrete structures to keep channel open, keep sand to side

30. Sea Wall

31. Groins and Jetties