The Dynamic Ocean Ch. 16

Currents move water from place to place

There are 2 kinds of currents…

Surface currents: move on or near surface of ocean First kind of current: Surface currents: move on or near surface of ocean Most are caused by wind Friction between wind blown air and the water surface causes the water to move Controlled by wind belts, earth’s rotational effect and location of continents

Surface Currents

What direction do most currents NORTH of the equator move?

CLOCKWISE!

What direction do most currents SOUTH of the equator move?

COUNTERCLOCKWISE!

Western side of ocean has warm currents traveling from equator Eastern side of ocean has cool currents moving toward equator

Examples of warm water currents: Gulf Stream Brazil Kuroshio

Examples of cold water currents: California current Canary current Labrador current

Second kind of current: 2. Deep density currents: cold, dense currents that flow very slowly beneath surface of ocean Occurs when denser seawater moves towards an area of less dense seawater

In the deep ocean, denser water around the Poles sinks and travels along the ocean floor toward the equator. At the same time, less dense water at the equator rises and moves towards the poles along the surface. These two events form a continuous cycle that circulate ocean water.

Wave Generating forces WIND TIDES Sometimes Earthquakes

Features of a wave CREST WAVE HEIGHT TROUGH WAVELENGTH

Wavelength Distance from one crest to another

Wave Height Difference between crest to trough

Period: The time it takes one wavelength to pass a given point

Speed= wavelength period

Test your knowledge… What is the speed of a wave 24 meters long with a period of 4 seconds?

Speed = 24 meters= 6 meters/sec

Observe an animation of wave motion.

Swells Group of long, rolling waves all about the same size Come at regular intervals

Height of wind-formed waves depends on 3 things… Length of time the wind blows Speed of wind FETCH: length of open water over which the wind blows in a single direction

As waves approach shore, the water is so shallow that they touch bottom. This happens at a depth of one-half the wavelength. As the wave scrapes bottom, the lower part of wave slows down and upper par moves ahead. The crest falls over and breaks onto the beach.

Observe waves as they break on the shore.

MAVERICKS

Waves and the shore: Breakers – foamy mass of water that washes onto shore Undertow Long shore current Tsunamis Rip current – strong surface currents that flow away from the beach; hazard to swimmers

TSUNAMIS

TSUNAMIS “Tidal waves” More appropriately called Seismic sea waves Long wavelength Long periods Low height – until they reach land!

http://www. geophys. washington http://www.geophys.washington.edu/tsunami/general/physics/characteristics.html

Rip Currents

What To Do if Caught in a Rip Current What should you do if you are caught in a rip current? First, REMAIN CALM! Signal to someone on the beach, a lifeguard or a friend, that you need help. If you are a strong swimmer, try to swim parallel to the beach until you are out of the rip current. Then swim toward the shore. Never try to swim back to shore directly against the Rip current, as this can exhaust and drown even the strongest swimmer. For the less confident swimmers, wade sideways parallel to the beach until you are out of the Rip’s pull, then swim back to shore.

Shoreline erosion is caused by: waves weathering rock chemical weathering storms

Shoreline Features sea stack: offshore, isolated columns of rock which was once connected to the headland

sea cliff: high, nearly vertical,steep structure that forms where waves strike directly against the rock

terraces: a nearly level platform that is found at the base of a sea cliff wave-cut: formed when a sea cliff is worn back wave-built: forms when eroded material is deposited

sea cave: large holes found in a sea cliff

spit: long, narrow deposit of sand connected at one end to the shore

The formation of a spit by sand movement in response to longshore currents.

tombolo: deposit that connects an offshore island to the mainland

sea arch: enlarged sea cave, produced when waves cut through the headland

Observe an animation showing the formation of an arch.

Evolution of Shoreline Features Makes no sense without caption in book

Examine an example of wave erosion.

beach: a deposit of sand or rock fragments along an ocean shore form where amount of fragments moving toward shore is greater than amount moving away

size and kinds of materials found on beaches vary widely Boulders more than 256mm Cobbles 64 to 256 mm Gravel 2 to 64 mm Sand .06 to 2 mm Silt less than 0.06mm

A close-up view of ordinary sand

Atlantic Coast white sand with quartz and feldspar erosion from Appalachian Mountains

Hawaii black/gray sand erosion from dark volcanic rock

each wave reaching the shore moves individual sand grains forward total action of thousands of waves moves sand a great distance sand piled up on shore producing sloping surface

berm: raised section at the back of the beach results from high tides or large storm waves

sandbar: long ridge of sand deposited offshore In winter, large storm waves remove sand from the beach and deposit it offshore sandbar: long ridge of sand deposited offshore In summer, waves return the sand to the beach

LONGSHORE CURRENT BACKWASH SWASH direction of sand drift BEACH

swash: motion of water up a beach the direction a wave approaches the shore determines sand grain movement swash: motion of water up a beach backwash: water that runs back down the beach under the next wave strong backwash is called an undertow

longshore current: movement of water parallel to and near the shore transport sand in direction parallel to shore may produce a spit or a tombolos

Processes that Affect Coastlines long term rising and falling of the sea level long term uplifting or sinking of land that borders water wave erosion and deposition The sea level is now rising at a average rate of about 1mm/yr

SUBMERGENT COASTLINES estuary: bay where freshwater and saltwater mix forms when sea level rises and sinks

EMERGENT COASTLINES barrier islands: long, narrow offshore ridges of sand many over 100 km long lie parallel to the shore about 3 km to 30 km offshore lagoon: narrow region of shallow water between barrier islands and shore

sometimes a hazardous place to live because it is severely eroded by storms

Barrier Islands Makes no sense without caption in book

Stabilizing the Shore  Protective Structures  Beach Nourishment • Groins, breakwaters, and seawalls are some structures built to protect a coast from erosion or to prevent the movement of sand along a beach.  Beach Nourishment • Beach nourishment is the addition of large quantities of sand to the beach system.

Miami Beach Before and After Beach Nourishment Makes no sense without caption in book

PRESERVING THE COASTLINE (two things that damage the coastline) recreation, commercial fishing, shipping, industrial and residential development pollution