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9/25/2018

OCN 201:Coastal processes

Drakes Estero , CA Cannon , OR

Barter , Alaska Lulworth , England

Question

Oil and natural gas are: A. formed from the remains of dead organisms B. renewable marine resources C. formed mainly in the deep D. none of the above

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The coastal zone are complex, diverse, and dynamic environments • More than half of the US population lives on the narrow coastal strip that covers 17% of the total land area of the country • Much of the population of other countries along the also lives within a small distance from the • The position of the coastline is not constant due to – Vertical movements of the crust due to tectonic activity (subsidence/uplift) – Eustatic changes – and

Coasts are shaped by marine and terrestrial processes

Classification of coasts • Erosional coasts: dominant processes remove coastal material • Depositional coasts: steady or growing due to the accumulation of or the action of living organisms (e.g. )

Sunset Cliffs, San Diego Bolonia Beach, Spain

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Erosional coasts • High energy coasts • Sea cliffs • Sea • Sea stacks • -cut platforms

Features of an erosional coast at low

Wave erosion of a sea produces a wave-cut platform visible at low tide

Sea cliff and wave cut platform The result of wave action on the coast

Cliffs Area of cliff recession

Wave cut platform

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Sea stacks The result of wave action on the coast

Over extended periods of time, shorelines are straightened by wave erosion Wave energy converges on and diverges in the adjoining bays. Sediment eroded from headlines accumulates as on relatively calm bays, eventually smoothing the contours of the .

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Depositional coasts and beaches

A beach is a zone of loose particles that covers a shore

What are the features of a beach? • Berm • Berm crest • Backshore • Foreshore • Beach scarp • Longshore trough • Longshore bars

Longshore transport Result of hitting the coast at an angle • Wave-driven movement of along exposed beach • -driven movement of sand in the

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Rip currents

Rip currents occur when water forced up the beach returns out to sea (these also provide a mechanism for moving sand offshore). The higher the surf, the greater the probability of rip currents

Question

What would you do if you are caught in a and you are being carried offshore? A. Swim as fast as I can towards the shore B. Slowly swim parallel to shore before returning to the beach C. Stop swimming and wait for rescue D. Swim away from the shore

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Other large-scale features of depositional coasts • Sand : that forms when the longshore current slows as it clears a and approaches a quiet . • Bay : sand spit that closes off a bay

Other large-scale features of depositional coasts • Barrier : narrow, exposed sandbars that are parallel to but separated from land • : a long, shallow body of isolated from the ocean • Sea islands: contain a firm central core that was part of the mainland when sea water was lower

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River deltas • that forms from deposition of carried by a • They form at places where sediment-laden enter enclosed or semi- enclosed

Mississippi Delta

Coast formed by biological activity

• Fringing grows around the perimeter of rising or static volcanic island • Island starts to sink isostatically, barrier reef develops as corals grow upward, separated from the island by a lagoon • Eventually the volcanic island sinks completely beneath the surface, leaving an where the barrier reef continues to grow upward

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Question

Who was the principal proponent of the theory of atoll formation: A. Alfred Wegener B. C. Arthur Holmes D. James Hutton

Estuaries An estuary is a where fresh river water mixes with ocean water

Types of esturaries: • Drowned river mouths: coastal river valleys with gentle sloping bottom • : narrow, steep, glacially eroded • Bar-built: when sand bars build along the coastline. Shallow, limited tidal action • Tectonic: formed by faulting and local subsidence.

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Characteristics of Characteristics of estuaries are determined by: • shape of the estuary • volume of river flow at the head of the estuary • range of at the mouth According to their circulation patterns they can be classified as: • Salt wedge estuary: rapidly flowing river, low to moderate . Exciting freshwater holds back a wedge of intruding seawater • Well-mixed estuary: slower flow, tidal range moderate to high. No vertical gradient in salinity, salinity increases from river to ocean • Partially mixed estuary: deeper, tidal range moderate to high, high river flow • estuary: where glaciers have gouged steep U-shape valleys bellow sea level. River water flows at the surface, little mixing with seawater

Erosion of Coastal Areas

Erosion of coastal areas occur: • where a beach has an insufficient supply of sand to replenish loss from coastal processes • when large (seasonal) waves and storm surge remove sand, some of which is not returned when waves subside • when rising sea level causes a beach to migrate landward and erode the /land behind it • when humans interfere with the natural sand supply, often resulting in sand starvation of the beach

All of the above drive a beach to seek new sand, usually by eroding the adjacent land

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Human interferences in coastal processes Groins cause differential erosion because of how they impact water flow and interrupt longshore transport of sand

Human interferences in coastal processes Seawalls protect property but increase beach erosion by deflecting wave energy onto the sand in front and beside them

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Human interferences in coastal processes Importing sand in response to erosion. New sand often is dredged offshore. Expensive. Can disturb aquatic biodiversity. Imported sand is normally finer than beach sand  it will erode faster

Question

Human interference with coastal processes has generally accelerated the erosion of coasts near inhabited areas: A. True B. False

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