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Depositional ShorelinesA bay barrier, or bay mouth bar, seals off a

lagoon from the ocean.A Tombolo is an sand bar that connects an

island to the mainland.Barrier islands are long offshore sand

deposits that parallel the coast.A spit connects at one end to the mainland

and hooks into a bay at the other.

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Depositional Shorelines

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Depositional Shorelines

Tombolo Barrier island

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Barrier IslandsCommon along East and Gulf coasts of the

United StatesDo not exist along erosional shorelinesProtect mainland from high wave activityCan migrate landward over time

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Barrier Island Anatomy

Ocean beachDunesBarrier flatHigh salt marshLow salt marshLagoon

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Barrier IslandOcean Beach – closest part of the island to

the ocean Dune – stabilized by grasses; protect lagoon

from strong stormsBarrier flat – grassy area that forms behind

dunes

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Barrier IslandHigh and low salt marshes – biologically

productive wetlandsGenerate peat deposits of decaying organic

matterLagoon – water between barrier island

and mainland

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Barrier IslandsMigrate landward

over time due to rising sea levels

Older peat deposits found on ocean beach

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Deltas Triangular deposits

of sediment where rivers empty into oceans or seasDistributaries carry sediment to ocean

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Emerging ShorelinesShorelines above current sea levelMarine terraces – flat platforms backed by

cliffs

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Submerging ShorelinesShoreline below current sea levelFeatures include

Drowned beachesSubmerged dune topographyDrowned river valleys (estuaries)

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Changing Sea LevelTwo major processes can change sea level:Local tectonic processesGlobal (eustatic) changes in sea level

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Changing Sea Level1. Local tectonic processes

Example: the Pacific coast of the United States is currently being uplifted.

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

ages

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Changing Sea Level2. Global (eustatic) changes in sea level

Sea level changes worldwide due toChange in…a. amount of available sea waterb. in ocean basin capacity

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Eustatic Changes in Sea Level Some MechanismsIce ages lock seawater up in ice (glaciation) –

sea level goes downIce melting after an ice age (deglaciation) –

sea level rises

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Pleistocene Epoch and TodayFrom 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).

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Global Warming and Changing Sea LevelGlobally averaged

temperatures – about 0.6°C (1.1°F) warmer over last 130 years

Sea level rose 10-15 cm (4-10 in) over past 100 years

As global warming continues, we will see a higher sea level.