Topic 18 Coasts, Beaches, and Estuaries GEOL 2503 Introduction to Oceanography

2 The coastal zone Southeastern United States Atlantic and Eastern Gulf of Mexico coasts. Broad, shallow continental shelves, typical of passive margins. What is the limit of the coastal zone?

3

4 Georgia beaches are made up predominantly of quartz sand.

Types of Coasts Erosional –A stretch of shoreline exhibiting erosion by marine processes Depositional –A stretch of shoreline where sediments carried by marine currents are deposited Both types may be present in the same area There are other types of coastal classifications 5

Erosional coastal features 6

7

Wave-Cut Platform and Marine Terrace 8

Sea Arch and Sea Stack 9

10 Depositional coastal features

Recall from Waves: 11

The longshore transport system moves sand parallel to the beach 12 Beaches are often called “rivers of sand”

13 Spits, also called sand spits, build in the direction of longshore sediment transport.

14

15 This baymouth bar (bay barrier) has been cut through for port access.

Divisions of the beach 16 ❷ ❸ ❶

17 Let’s say “storm” instead of “winter” and “fairweather” instead of “summer.”

Barrier Islands Barrier islands are low ridges of sand that parallel the coast 3 to 30 kilometers offshore –Found mainly along the Atlantic and Gulf Coastal Plain –Most are 1 to 5 kilometers wide and 15 to 30 kilometers long –Probably form in several ways Some originate as spits Some originate from sand piled up offshore Some are flooded sand dunes from the last glacial period 18

19 A.Salt marsh B.Dune C.Peat bed D. Barrier flat E. Ocean beach F. Estuary of lagoon

20 Georgia’s coast is lined with beautiful barrier islands. Only four of them are accessible by car: Tybee, St. Simons, Sea Island, and Jekyll. The rest are mostly undeveloped and preserved.

Video Watch the learner.org video on Waves, Beaches and Coasts to see more about shallow water waves An episode of the “Earth Revealed” series mlhttp:// ml 21

Tidal Inlets Recall flood tides and ebb tides Water moving in and out of channels between barrier islands (called tidal inlets) also moves sediment in and out of the inlets The amount of water moving in and out of an inlet is controlled by the tidal range and the size of the water body behind the barrier islands 22

23

Estuary vs Lagoon Both are semi-enclosed coastal bays Estuaries have fresh water input, low salinity Lagoons have limited fresh water input, often hypersaline “Sound” is another term for coastal estuary or lagoon behind a barrier island 24

Estuaries Estuaries are the mixing zones of river water and sea water They may be river mouths or coastal bays They typically have restricted connection to the ocean and salinity lower than that of seawater They are important ecosystems 25

Little fresh water input Major fresh water input 26

Typical of North Carolina Inlets 27

Typical of Georgia Inlets 28

Isabel Inlet, 17 Sep 2003 Image: 23 Sep 1999 Outer Banks of North Carolina Cape Hatteras 29

Hurricane Isabel breach, Hatteras Island, NC. Photo taken Sept. 21, Courtesy Duke University Program for the Study of Developed Shorelines. 30

Tidal inlets can open and close over time. Usually they are opened during storms, and closed by longshore transport during fair weather. 31

Changing Sea Level Sea level rises and falls largely controlled by land ice volume Glaciation is a time of increasing volume of land ice, thus sea-level fall Deglaciation is a time of decreasing volume of land ice, thus sea-level rise We currently are in a period of land ice melting and sea level rise Sea-level rise becomes a natural hazard when rising water level encroaches upon human development Difficult for coastal communities to incorporate into planning regulations 32

33

34

Sea-level rise during the past 100+ years has been about cm total. Global warming may increase this rate. 35

36

37

Barrier island migration Movement landward over time Associated with rising sea levels Older peat deposits found on ocean beach 38

How did the Georgia coast end up looking like this? The features in yellow are ancient barrier islands constructed during higher sea levels. Shoreline nameElevation above today’s sea level Estimated age Wicomico30 m1.5 Ma Penholoway21 m1 Ma Talbot13 m ka Pamlico7 m ka Princess Anne4 m80-40 ka Silver Bluff1.5 m40 ka Holocene (modern)Sea level<10 ka Ma = million years ago, ka = thousand years ago, Holocene is the name of the current geologic epoch 39

Cross-section of the lower Georgia coastal plain. See how the older the barrier island complexes are, the higher elevation and further inland they are. See ages, elevations, and distance inland on previous slide. Holocene is the name of the current geologic epoch. The Holocene barrier island system is what is active today. From Henry (1968). 40

41