1. Exit Choose to view chapter section with a click on the section heading. ►Coastal ClassificationCoastal Classification ►Coastal DynamicsCoastal Dynamics ►Biological Processes and Human ActivityBiological Processes and Human Activity Chapter Topic Menu

2. MenuPreviousNext 13 - 2 Two Classification Systems nThe first classification is based on geologic processes.  Active Coasts nClose to plate boundaries nResult in volcanic activity and earthquakes nExamples: West Coast, the Ring of Fire.  Passive Coasts nFar away from active plate boundaries nExample: East Coast Coastal Classification Chapter 13 Pages 13-3 to 3-5

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4. MenuPreviousNext Two Classification Systems nThis second classification system is based on short-term coastal processes.  Primary Coasts: Formed by nonmarine geologic processes over a long period of time.  Secondary Coasts: Formed by marine action, process takes much less time. 13 - 4

5. MenuPreviousNext 13 - 5 Types of Primary Coasts nSedimentation Coasts  Form from materials carried by rivers are deposited in the ocean (Nile delta in Egypt) nVolcanic Coasts  Formed by volcanic activity (Hawaiian Islands). Coastal Classification Chapter 13 Pages 13-5 to 13-8

6. MenuPreviousNext Nile Delta 13 - 6 Sediment Deposition From Nile river

7. MenuPreviousNext Types of Primary Coasts nTectonic Activity Coasts  Formed by tectonic activity as plates collide. (Tomales Bay, California) nLand-based Erosion Coasts  Form from river erosion on land during periods of low sea level; the eroded area floods when sea level rises.  Chesapeake Bay 13 - 7

8. MenuPreviousNext Tomales Bay,California 13 - 8 Tomales Bay Formed by motion on the San Andreas fault

9. MenuPreviousNext Chesapeake 13 - 9 Tomales Bay Path of ancient river valley; now flooded

10. MenuPreviousNext Types of Secondary Coasts nWave-erosion Coasts  Created by wave erosion on the coastline  Results in sea caves, arches and sea stacks nMarine-deposition Coasts  Ocean sediments accumulate on the coast  Creates barrier islands, beaches, salt marshes, and mud flats nMarine Organism Coasts  Coasts built by structures made by marine organisms  The Great Barrier Reef of Australia 13 - 10

11. MenuPreviousNext Wave Erosion and Deposition 13 - 11

12. MenuPreviousNext Great Barrier Reef 13 - 12

13. MenuPreviousNext 13 - 13 Longshore Drift nOne of the most significant forces shaping the coast is longshore drift. nLongshore drift is created by the tendency for materials to move along the coastline due to a longshore current. This is how it works: 1.Waves arrive on shore at somewhat of an angle, but the water recedes at nearly a 90º angle. 2.Sand and sediment flow back with the water at this angle. 3.The net motion of this backwash combines with the net motion of the waves to cause a longshore current. 4.Longshore drift occurs as the current moves material down the coast. Coastal Dynamics Chapter 13 Pages 13-12 & 13-13

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15. MenuPreviousNext 13 - 15 Where Sand Comes From nSand comes from erosion. It may be from the effect of waves pounding the shoreline or inland erosion. nIn tropical regions sand also comes from biological sources, like the erosion of coral reefs.  Example: Parrot Fish Coastal Dynamics Chapter 13 Pages 13-13 to 13-15

16. MenuPreviousNext 13 - 16 Large Scale Sand Features nA spit is a length of sand that extends perpendicular to the beach. Spits form when a longshore current slows. Sand settles out of the water, forming the spit. nTombolos are spits that extend between two islands or from an island to the mainland. Tombolos form when the longshore current slows. nDeltas are triangular areas of sediment formed when sediment is deposited at the mouth of a river. Coastal Dynamics Chapter 13 Page 13-16

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18. MenuPreviousNext Tombolo 13 - 18

19. MenuPreviousNext Delta 13 - 19

20. MenuPreviousNext 13 - 20 Large Scale Sand Features (continued) nBarrier Islands are long islands of sand that run parallel to the coast. nThere are currently two theories on how they form.  1. Sediment accumulates offshore, eventually building up into an island.  2. They were giant sand dunes that became islands with the last major sea-level rise. Coastal Dynamics Chapter 13 Pages 13-17 to 13-19

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22. MenuPreviousNext 13 - 22 Coral Reefs nCoral is perhaps the most significant of all biological processes that affect the coast. Coral reefs can be massive, but only the outside layer, the coral polyps, is alive.  Individual polyps create a calcium carbonate external skeleton as they grow. It is this part of its structure that creates coral reefs. Biological Processes and Human Activity Chapter 13 Pages 13-21 & 13-22

23. MenuPreviousNext Coral Reefs nFringing reefs lie along an island or mainland coast. nBarrier reefs have a similar structure as fringing reefs, but lie further from shore. nAtolls are ring-shaped coral reefs that encircle a shallow lagoon. 13 - 23

24. MenuPreviousNext 13 - 24 Plant Communities nAlong low energy coasts, plant communities can dominate the coast.  Seagrasses live entirely underwater, but most marine plants live partly out of the water. nAmong the most important of the plant-dominated shorelines are the mangrove swamps.  Mangroves affect the coast directly by holding sediment in place and absorbing wave energy. Biological Processes and Human Activity Chapter 13 Pages 13-23 & 13-24

25. MenuPreviousNext Human Activities nHuman-built coastal structures include:  Groins are artificial protrusions jutting out perpendicular to the shore. They are designed to block longshore drift.  Jetties are the same as a groin, except they are built to reinforce a harbor entrance.  Breakwaters run parallel to shore or start on shore and curve into the sea.  Seawalls stand either at the water along the shore or at the top of a beach. They act as a barrier to block the waves from eroding the land. 13 - 25

26. MenuPreviousNext Human Activities (continued) nProblems:  Jetties and groins block longshore drift.  Seawalls effectively absorb energy but unprotected land next to the seawall tends to suffer from increased erosion. nSolutions: nBeach renourishment  Bringing in sand to replenish eroded sand  It is expensive and is only a temporary fix. nThe likely solution to problems created by human structures is a change in coastal attitudes and management 13 - 26 Biological Processes and Human Activity Chapter 13 Pages 13-24 & 13-25