Oceanography Chapter 7 and 8 Alec Gatewood

For deep-water waves, the diameter of the orbit of a water particle at the ocean surface is equivalent to the wave height.

(There is no net horizontal transport of water mass)

How might barrier islands form?

1. Higher sea level submerged beaches and isolated the tops of dune ridges as offshore islands 2. Vertical growth of a submarine sand bar 3.Sand spits lengthened into barrier islands via longshore sand transport; spit was then breached during a storm event, disconnecting it from the mainland. Barrier islands are a form of protection for mainland coastal structures from storm surge and waves

The size of wind-generated waves depends on what three factors?

1. Wind Speed 2. Duration of Wind 3. Fetch (The distance wind blows in the same direction)

What is a rip current and why do rip currents develop?

A rip current can be identified by something that goes near the shoreline, through the surf zone, and past the line of breaking waves. They develop when a longshore current is interrupted and has a seaward return flow. They can occur where breaking waves are found. They are induced by physical (man-made) barriers, such as piers and groins.

Distinguish between two types of coastal wetlands.

A salt marsh: Contains salt tolerant plants that colonize shores. These plants protect coastline from storm wave erosion, they filter runoff, and provide a habitat for crabs and oysters. Mangrove Forests: Salt tolerant woody trees found in subtropical and tropical climates which provide habitat for land and marine animals and protect the coastline from storm wave erosion. Cassiopeia, Mari-culture, and red white and black trees

What is a seiche and how does it differ from wind-driven ocean waves?

A seiche is a rhythmic oscillation of water in an enclosed basin; their crests alternate vertically with troughs at fixed locations. Unlike wind-driven progressive waves, a seiche is a standing wave. The maximum vertical motion of the water in a seiche takes place at the antinodes and the maximum horizontal motion occurs at the node.

What effect does cliff erosion tend to have on a rocky coastline over time?

A shoreline is straightened Process: Waves Slow as they approach the headland, creating a high concentration of wave energy and reducing the energy reaching the bay. Stages: 1. Youth (Headlands and no Bays) 2: Maturity (Headland Cove beaches and sand spits sea cliffs stacks and arches and wave-cut platforms) 3: Old Age (Headlands eroded and bays are filled with sediments)

In terms of plate tectonics, what is the difference between an active vs. passive margin? How does the profile of an active vs passive margin differ? Which type is the east coast of the U.S? The West Coast of the U.S?

Active Margin: A continental margin where there is significant volcanic/earthquake activity (Usually Convergent and Erosional: Predominantly loses shoreline-rocky WEST COAST U.S.A). Emergent (Shoreline rising above sea level) Passive Margin: A geologically quiet continental Margin far removed from a plate boundary (Depositional Coasts: Predominantly gains sediment-sandy EAST COAST U.S.A). Submergent (Shoreline Sinking below sea level)

Along which type of coastline might you find wave cut platforms and raised beaches? Drowned valleys and fjords? Which type if the coast of the Southeast U.S.A? The Pacific Northwest?

An emergent coastline has raised beaches and wave cut platforms. A submergent coastline will have drowned valleys and fjords. Southeast to U.S.A: Submergent (Shoreline sinking below sea level) The Pacific Northwest: Emergent (Shoreline rising above sea level) ADDITIONAL TERMS: Wave cut platform: Flat Surface cut into rock by wave action when sea level was higher relative to coast Raised beach: A beach that has become stranded above sea level due to isostatic rebound ( Post-glacial rebound) of land surface Drowned Valley: Former floodplain that has been flooded by sea level rise Fjord: A glacially carved valley flooded by sea level rise

What is anti-estuarine circulation?

Anti-estuarine circulation occurs in arid coastal regions that receive less freshwater input than is lost through evaporation; in these, vertical circulation patterns are opposite those in most estuaries. The landward-flowing surface waters replace waters lost through evaporation. The Red Sea and the Mediterranean Sea have this circulation pattern.

Describe the migration of barrier islands that is expected to occur with sea level rise.

As sea level rises, barrier islands migrate landward.

Where specifically is the development of internal waves most likely to occur in the ocean water column?

Base of the mixed layer Between distinct water masses In estuaries along the pycnocline between fresh river water and salty ocean water

Why do beaches typically have less sand in the winter?

Beaches have less sand during the winter because storm waves transport sand offshore where it is stored in longshore bars. High energy waves: Short, high waves Longshore bars: Offshore sandbars that parallel the coast

What tends to happen to a beach behind a breakwater?

Breakwater: Built to moderate wave action on the shoreline. Doing this can result in deposition of sediment in the low-energy zone behind the breakwall and in erosion down-current from it.

Compare the restoring force for capillary waves versus longer wavelength ocean waves.

Capillary waves: surface tension is the restoring force. Longer Wavelength Ocean Waves: gravity is the restoring force.

Name two irreversible consequences of over-pumping groundwater in coastal areas.

Deplete the freshwater lens and destroys aquifer- draws salt water. Once salt water begins to be drawn, the aquifer can never be replenished. The sea water will seep into the freshwater lens. As a result of over-pumping ground water in coastal areas, you can also compact sediments which revokes the ability to store water, causing sunken land (subsidence).

In what direction does the hooked tail of a spit point?

Down and in, the direction of the longshore current. Spit: Deposit of sand with a hooked tail that points in the direction of the longshore current

What are the purposes of groins and jetties. What are they? What is the difference between the two? How does their installation affect shoreline depositional/erosional patterns?

Groin: A groin is used to trap sand as it is moved by the longshore current. A groin does not completely interrupt the longshore current but it does accumulate sand on the updrift side. Creates a serrated look in the beach. Jetty: A jetty is used to connect land with water further from the shore for docking ships and unloading cargo. A jetty is typically longer and creates larger uplift of sand due to complete redirection of the longshore current. Causes major accumulation of sand which reduces sand on other side making a need for dredging.

During what time of year do hurricanes occur most and why?

Hurricanes occur mainly in mid-september. Ocean water needs to be at least 26.5C and 45M in depth.

How are hurricanes identified internationally?

Hurricanes: North Atlantic/ Eastern Pacific Typhoons: Western Pacific Tropical Cyclones: Indian Ocean Willi-Willis: Australia

For the same wind speed, are higher waves generated with increasing or decreasing fetch?

Increasing.

Hurricane Identification:

Km/h 120-153 (1) 154-177 (2) 178-209 (3) 210-249 (4) >250 (5) Storm Surge Meters: 1.2-1.5 (1) 1.8-2.4 (2) 2.7-3.7 (3) 4.0-5.5 (4) >5.8 (5) Damage Minimal (1) Moderate (2) Extensive (3) Extreme (4) Catastophic (5)

What is the littoral drift? What is the average direction of the littoral drift along the east and west coasts of the U.S?

Littoral Drift: The net transport of sediment (sand) parallel to the shore. Average Direction: North to South

What is the longshore current and how is it created?

Longshore Current: When water moves in a zigzag fashion along the shore and creates a net transport of water parallel to the coastline (Transport of water); this is caused by waves near parallel approach to the shore.

Sketch a wave and label the following features: crest, trough, height, and wavelength. How do you determine the period and frequency of a wave?

Period is found by dividing velocity by frequency. Frequency is found by dividing velocity by wavelength.

Sketch a spit, barrier island, and tombolo. Are these features of erosional or depositional shorelines?

Refer to question 10 on the Dynamic Coastlines packet, and these found on depositional shorelines.

How can Rip currents be identified?

Rip currents are identified as a low spot due to a break in a sand bar; this spot provides the channel for the current. What to look for: A channel of churning, choppy water An area having a notable difference in water color (Typically murky almost like a turbidity current) A line of foam, seaweed, or debris moving steadily seaward A break in the incoming wave pattern

What is a rogue wave, and how are rogue waves created?

Rogue waves are unusually high waves that occur in the open ocean, as well as some coastal areas. Considered rogue when 2.2 times or more times the significant wave height(Average height of tallest third of waves observed in that patch of ocean.) These waves can occur in any type of weather. Less than 3% chance during any hour. There is little or no warning. Famous rogue waves: USS Ramapo (112 ft) Norwegian Dawn 2005 7 story wave.

Distinguish among the three types of estuaries in terms of freshwater/ seawater flow and vertical stratification.

Salt Wedge: Where inflow of river dominates, minimal mixing. Two Stratified layers of water. Wedge of fresh water overlies denser wedge of seawater. Partially Mixed: Neither river discharge nor tidal currents dominate. Vigorous vertical mixing. Weak stratification and halocline. Chesapeake Bay: The largest partially mixed estuary in the U.S. Well Mixed: Tides dominate, extensive mixing. No halocline and no vertical stratification. No salinity gradient. Halocline: The vertical transition zone where salinity changes between two layers of water. Salt Wedge: Significant halocline Partially Mixed: Weak halocline Well mixed: No halocline

What is often the most dangerous aspect of a hurricane?

Storm Surge: Dome of seawater 80-160km wide driven onshore by strong winds.The storm surge can hit a high tide, creating unpredictable and high flooding.

How to escape a rip current:

Swim parallel to the shore. Moreover, swim at right angles to the rip current.

For a seiche, where are the wave heights the highest?

The antinodes.

How does beach profile change during the winter?

The longshore bars grow and the berm sinks. A wintertime beach typically has rocky narrow berm and a flattened beach face.

What is the primary source of energy for a hurricane? How does this differ from a thunderstorm?

The main source of energy are warm waters and condensation from the ocean. This differs from a thunderstorm, for a thunderstorm is caused by a cold front pushing a warm from up releasing moisture and colliding two temperatures.

As waves enter shallow water, what happens to the wavelength? What about the wave height?

The wavelength decreases, and the wave height increases drastically.

What causes most waves on the ocean surface?

The wind causes most waves. Seismic activity and tidal forces are two other wave causers.

Why are the Florida Everglades threatened?

There is a decreased flow of water from lake Okeechobee. 1,400 miles of channels and levees divert the water for irrigation and residential use. It was once 11,000 square km, it now covers less than 5000 square km.

Why are tsunamis classified as shallow-water waves?

Tsunamis are classified as shallow water waves because they have a very long wave length and a very short wave height. Once the tsunami begins to reach shallow water the water molecules have no place to go but up. The amount of water is forced to condense, causing it to increase in height and decrease in length.