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ChapterChapter 1 10 Clickers Lecture Essentials of Eleventh Edition

The : and Shoreline Processes

Alan P. Trujillo Harold V. Thurman

© 2014 Pearson Education, Inc. Chapter Overview

• Coastal regions have distinct coastal features. • The is a dominant coastal feature. • Waves affect and of . • level changes affect the coast. • Different have different characteristics. • Humans have attempted various coastal stabilization measures.

© 2014 Pearson Education, Inc. Defining Coastal Regions

• General Features • – the zone that lies between the low line and the highest area on land affected by storm waves • Coast – extends inland as far as related features are found • Coastline – boundary between shore and coast

© 2014 Pearson Education, Inc. Terminology

© 2014 Pearson Education, Inc. Defining Coastal Regions

• Backshore – part of shore above high tide shoreline • Foreshore – part of shore exposed at low tide and submerged at high tide • Shoreline – ’s edge that migrates with the tide

© 2014 Pearson Education, Inc. Defining Coastal Regions

• Nearshore – extends seaward from low tide shoreline to low tide breaker line • Offshore – zone beyond low tide breakers • Beach – wave-worked deposit of the shore area – Area of beach above shoreline often called the recreational beach • Wave-cut bench – flat, wave-eroded surface

© 2014 Pearson Education, Inc. Defining Coastal Regions

• Berm – dry, gently sloping, elevated beach margin at the foot of coastal cliffs or sand • Beach face – wet, sloping surface extending from berm to shoreline – Also called low tide terrace

© 2014 Pearson Education, Inc. Defining Coastal Regions

• Longshore bars – sand bars parallel to coast – May not always be present – Can cause approaching waves to break • Longshore trough – separates longshore bar from beach face

© 2014 Pearson Education, Inc. Composition of Beaches

• Formed from locally available material • May be coarse or fine grained sediment – Boulders from local cliffs – Sand from – Mud from rivers • Significant biologic material on tropical beaches – Example: material • Material is always in transit along the shoreline.

© 2014 Pearson Education, Inc. Seasonality of beach conditions

© 2014 Pearson Education, Inc. Sand Movement Along Beach

• Perpendicular to shoreline (toward and away) – – water rushes up the beach – Backwash – water drains back to the ocean • Parallel to shoreline (up-coast or down-coast) – Longshore – transports sand along the beach

© 2014 Pearson Education, Inc. Summertime Beach

• Light wave activity – Wide, sandy berm – Steep beach face – Swash dominates • Longshore bars not present • Generally milder storms

© 2014 Pearson Education, Inc. Wintertime Beach

• Heavy wave activity – Backwash dominates – Sediment moved away from shore – Narrower beach – Flattened beach face • Longshore bars are present • Stormy

© 2014 Pearson Education, Inc. Light vs. Heavy Wave Activity

© 2014 Pearson Education, Inc. Longshore Current

• Zigzag movement of water along shore • Longshore currents travel at speeds up to 4 km (2.5 miles) per hour

© 2014 Pearson Education, Inc. • Also called longshore transport, beach drift, or littoral drift • Transports beach sediment in a zigzag fashion in the direction of the longshore current • Occurs in

© 2014 Pearson Education, Inc. Longshore Drift

• Millions of tons of sediment moved yearly • Direction of transport changes due to wave approach • Net sediment movement is southward along the Atlantic and Pacific coasts of the .

© 2014 Pearson Education, Inc. Beach Drift and Longshore Currents

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Two Major Types of

• Erosional Shores – Well-developed cliffs – Exist where tectonic uplift of coast occurs – U.S. Pacific coast is one example • Depositional Shores – Gradually subsiding shore – Barrier and sand deposits are common.

© 2014 Pearson Education, Inc. Erosional Shores

• Protruding bits of land called absorb much wave . • Wave-cut cliffs and sea caves are other features carved out by wave activity.

© 2014 Pearson Education, Inc. Erosional Shores

• Sea arches form where sea caves in headlands erode all the way through. • Sea stacks form when the tops of sea arches erode away completely.

© 2014 Pearson Education, Inc. Erosional Shorelines

• Uplift of wave-cut bench generates a marine terrace. • Wave erosion increases with – More shore exposed to open ocean – Smaller – Weaker bedrock

© 2014 Pearson Education, Inc. Depositional Shorelines

barrier, or bay – seals off a from the ocean • – sand bar that connects an to the mainland • Barrier islands – long offshore sand deposits that parallel the coast • – connects at one end to the mainland and hooks into a bay at the other

© 2014 Pearson Education, Inc. Depositional Coast Features

© 2014 Pearson Education, Inc. Bay Barrier, Martha’s Vineyard, MA

© 2014 Pearson Education, Inc. Tombolo, Goat Rock Beach, CA

© 2014 Pearson Education, Inc. Barrier Islands

• Extremely long offshore deposits of sand parallel to coast • Do not exist along erosional shorelines • Protect mainland from high wave activity • Appear to have developed at end of last 18,000 years ago © 2014 Pearson Education, Inc. Barrier Islands

• Separated from mainland by lagoon • Attractive building sites because of proximity to ocean • Many structures destroyed by ocean or required relocation

© 2014 Pearson Education, Inc. Heavily Developed , NJ

© 2014 Pearson Education, Inc. Barrier Islands

• More than 2000 barrier islands identified worldwide • Almost 300 along Atlantic and coasts of U.S.

© 2014 Pearson Education, Inc. Barrier Island Features

• Ocean Beach – closest part of the island to the ocean • – stabilized by grasses; protect lagoon from strong storms • Barrier flat – grassy area that forms behind dunes • Salt marshes – inland of barrier flat – Low marsh extends from mean to high neap tide line. – High marsh extends to highest tide line.

© 2014 Pearson Education, Inc. Barrier Island Features

© 2014 Pearson Education, Inc. Barrier Islands • Migrate landward over due to rising sea levels • Older peat deposits found on ocean beach

© 2014 Pearson Education, Inc. Deltas

• Triangular deposits of sediment where rivers empty into or • Distributaries – branching channels carry sediment to ocean

© 2014 Pearson Education, Inc. Mississippi

1973 1989 2003

© 2014 Pearson Education, Inc. Deltas

• Delta shoreline is smoothed when erosion exceeds deposition. • Nile Delta currently eroding

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Sand colors say something….

© 2014 Pearson Education, Inc. Sea arches and sea stacks.

© 2014 Pearson Education, Inc. Erosional Features off Owen Point, Victoria

© 2014 Pearson Education, Inc. WA

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Primary or Secondary?

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Beach Compartments

• Three major components: 1. Rivers that supply beach sediment 2. Beach itself 3. Offshore submarine canyons • Beach starvation – human activities block supply of sand to beach compartments

© 2014 Pearson Education, Inc. Beach Compartments

© 2014 Pearson Education, Inc. Emerging Shorelines

• Shorelines above current sea level • Marine terraces – flat platforms backed by cliffs • Stranded beach deposits – Indication that former shoreline has risen above sea level

© 2014 Pearson Education, Inc. Submerging Shorelines

• Shoreline below current sea level • Drowned beaches • Submerged dune topography • Drowned river valleys

© 2014 Pearson Education, Inc. Changing Sea Level

Two major processes can change sea level: • Local tectonic processes raise or lower ’s crust • Worldwide changes in sea level

© 2014 Pearson Education, Inc. Changing Sea Level

• Tectonic Movements – Include crustal uplift or subsidence and localized folding, faulting, and tilting – Example: The Pacific coast of the United States is currently being uplifted.

© 2014 Pearson Education, Inc. Changing Sea Level

• Isostatic adjustments – rebound of Earth’s crust after removal of heavy loads or sinking with application of heavy loads – Ice loading from glaciers during ice ages

© 2014 Pearson Education, Inc. Changing Sea Level

• Eustatic sea level changes – worldwide • Can be caused by – Formation or destruction of inland lakes – Sea floor spreading rate changes – Formation or melting of glaciers – Thermal expansion or contraction of

© 2014 Pearson Education, Inc. Epoch and Today

• From about 2 million to 10,000 years ago, a series of four ice ages affected Earth. • Sea level was at least 120 meters (400 feet) below today’s sea level. • If all remaining ice on Earth melted today, sea level would rise another 70 meters (230 feet).

© 2014 Pearson Education, Inc. U.S. Coasts • Three coasts: – Atlantic coast – Pacific coast – Gulf coast • Each has its own unique characteristics.

© 2014 Pearson Education, Inc. Atlantic Coast

• Most coasts open to storm wave attack • Barrier islands common from Massachusetts south • Bedrock – Florida bedrock is resistant limestone. – Northward through New Jersey is composed of easily erodable recent deposits. – New York through has glacier-affected rocks.

© 2014 Pearson Education, Inc. Atlantic Coast

• Strong storms called nor’easters can damage the coast north of Hatteras, NC. • Nor’easters can generate storm waves up to 6 meters (20 feet).

© 2014 Pearson Education, Inc. Atlantic Coast

• Average erosion is 0.8 meter (2.6 feet) per year; sea is migrating landward • Delaware, New York, and Georgia have the most serious erosion problem. • Northern Maine may still be rebounding from last ice age – sea level dropping

© 2014 Pearson Education, Inc. Atlantic Coast

• Barrier islands • Drowned river valleys – Common – Form large bays

© 2014 Pearson Education, Inc. Gulf Coast

• Low tidal range • Generally low wave energy • Tectonically subsiding • Mississippi delta dominates – Locally sea level rises due to compaction of delta • Average rate of erosion is 1.8 meters (6 feet) per year.

© 2014 Pearson Education, Inc. Pacific Coast

• Tectonically rising • Experiencing less erosion than Atlantic or Gulf coasts • Open exposure to high energy waves • Average rate of erosion 0.005 meter (0.016 feet) per year

© 2014 Pearson Education, Inc. Hard Stabilization

• Structures built to decrease and interfere with sand movement • Also called armoring of the shore • Often results in unwanted outcomes – Some structures may increase wave erosion.

© 2014 Pearson Education, Inc. Hard Stabilization

• Four major types of stabilization structures: 1. Groins and groin fields 2. 3. Breakwaters 4.

© 2014 Pearson Education, Inc. Groins and Groin Fields

• Built perpendicular to the beach – Often made of rip rap, or large blocky material • Traps sand upcoast, which can cause erosion downstream of the longshore current

© 2014 Pearson Education, Inc. Groins and Groin Fields

• Upcoast trapping of sand may necessitate a groin , or a series of groins built along a beach. • Sand is distributed differently, but no additional sand is on the beach.

© 2014 Pearson Education, Inc. Jetties • Similar to groin • Built perpendicular to shore • Built in pairs • Built to protect entrances

© 2014 Pearson Education, Inc. Jetties at Santa Cruz Harbor, CA

© 2014 Pearson Education, Inc. Breakwaters

• Built parallel to a shoreline • Designed to protect from waves • Can cause excessive erosion, requiring dredging to keep area stable

© 2014 Pearson Education, Inc. at Santa Barbara, CA

© 2014 Pearson Education, Inc. Breakwater at Santa Barbara, CA

• Between 1931 and 1949, breakwater disrupted longshore transport of sand

© 2014 Pearson Education, Inc. Seawalls

• Destructive to environment • Designed to coastline and protect human developments • One large storm can remove beach • Wave activity eventually undermines structure; need continual repair or will collapse

© 2014 Pearson Education, Inc. Seawall Damage

© 2014 Pearson Education, Inc. Alternatives to Hard Stabilization

• Three major alternatives 1. Construction restrictions 2. Beach replenishment 3. Relocation

© 2014 Pearson Education, Inc. Alternatives to Hard Stabilization

• Construction restrictions – Simplest alternative – Limit building near shorelines – Paradoxically, National Insurance Program encouraged construction.

© 2014 Pearson Education, Inc. Alternatives to Hard Stabilization

• Beach replenishment – Sand added to beach/longshore current – Expensive; costs between $5 and $10 per cubic yard – Sand must be dredged from elsewhere.

© 2014 Pearson Education, Inc. Beach Replenishment

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Coastal Stabilization Structures

© 2014 Pearson Education, Inc. Alternatives to Hard Stabilization

• Relocation – Move structures rather than protect them in areas of erosion – Can allow humans to live in natural balance with beach processes

© 2014 Pearson Education, Inc. Cape Hatteras

© 2014 Pearson Education, Inc. © 2014 Pearson Education, Inc. Salt marshes and swamps

© 2014 Pearson Education, Inc.