Agents of Erosion & Deposition

Ch. 11

What is Wind Deposition?

when the wind stops, it drops its load

What are Dunes? mounds of wind blown sand

•form where soil is dry and unprotected and the wind is strong

How do dunes form?

when a barrier slows the speed of the wind, it causes sand to accumulate on the sheltered side, sand accumulates on exposed side, and eventually buries the barrier

Wind causes saltation, or jumping grains, on the windward side of sand dunes

windward

crest

slipface

barchan dune: crescent shaped, open side faces away from wind, common, found in deserts

parabolic dune: crescent-shaped, open sided faces into the wind

transverse dune: series of ridges of sand in long, wave-like patterns- form at a right angle to the wind

longitudinal dune: ridges of sand in long, wave-like patterns- lie parallel to the wind direction

This Landsat image reveals sand dunes advancing on Nouakchott, the capital of Mauritania.

Alien dunes. NASA's Mars Global Surveyor photographed these sand dunes on Mars

What is a 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

What is a berm? raised section at the back of the beach

•results from high tides or large storm waves

What is a sandbar?

•long ridge of sand deposited offshore

•In winter, large storm waves remove sand from the beach and deposit it offshore

•In summer, waves return the sand to the beach

BEACH

direction of sand drift

LONGSHORE CURRENT

SWASH BACKWASH

What is a swash? motion of water up a beach

What is a backwash? water that runs back down the beach under the next wave

•strong backwash is called an undertow

What is longshore current?

movement of water parallel to and near the shore

•transport sand in direction parallel to shore

What causes shoreline erosion?

1.waves weathering rock

2. chemical weathering

3. storms

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

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

What are the Shoreline Depositional Features?

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

What are the Processes that Affect Coastlines?

1.long term rising and falling of the sea level

2.long term uplifting or sinking of land that borders water

3.wave erosion and deposition

The sea level is now rising at a average rate of about 1mm/yr

What are SUBMERGENT COASTLINES?

•estuary: bay where freshwater and saltwater mix

•forms when sea level rises and sinks

What are 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

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

Barrier Islands

Protective Structures

• 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.

How do we Stabilize the Shore?

Miami Beach Before and After Beach Nourishment

PRESERVING THE COASTLINE

(two things that damage the coastline)

1. recreation, commercial fishing, shipping, industrial and residential development

2. pollution

The Ocean Floor

Ch. 14

The Topography of the Ocean

What percent of the Earth’s surface is covered by

Oceans?

70%!

Earth has four Oceans

Which one is the largest?

Covers 30% of surface of the Earth

Which one has the longest distance North to South?

Which one is mostly in the Southern Hemisphere?

Which one is the smallest?

Bathymetry is the measurement of ocean depths and the charting of the shape or topography of the ocean floor.

Today’s technology allows scientists to study the ocean floor in a more efficient and precise manner than ever before.

Sonar •an acronym for sound navigation and ranging. It is also referred to as echo sounding•works by

transmitting sound waves toward the ocean bottom

Sonar Methods

Sonar systems on the research vessel Moana Wave

Satellites •able to measure small differences by bouncing microwaves off the ocean surface

•differences in the height of the ocean surface are caused by ocean-floor features

Satellite Methods

Submersibles

•are small underwater crafts used for deep-sea research

•Today, many submersibles are unmanned and operated remotely by computers. These remotely operated vehicles (ROVs) can remain underwater for long periods

The ocean floor is divided into two parts:

•the continental margin

•ocean basin floor

continental margins: shallower portions of the ocean floor made of continental crust

Continental Margin

•continental shelf: gently sloping part of the continent that is covered by ocean water

•continental slope: steeper slope at the seaward edge of the shelf

•continental rise: raised wedge at the base of the slope formed from sediments that have moved down the slope (formed from rocks and animal remains)

turbidity currents: very dense currents that carry large amounts of sediments down the slope

submarine canyon: deep valleys in the slope and shelf caused by turbidity currents (V-shaped)

Submarine Canyons

ocean basin floor: portion of the basin made up of oceanic crust

abyssal plains: extremely flat parts of the ocean floor

seamounts: isolated volcanic island

Seamounts east of Adare. Seamounts mapped with multi-beam bathymetry

Close-up of three seamounts, East Pacific Rise, which rise 6000 to 7000 feet (1800-2100 m) from the sea

guyots: flat-topped, submerged seamounts

trenches: deep, long, narrow valley in the ocean floor

mid-ocean ridge: system of undersea mountain ranges that wind around the Earth

Ch. 15

Ocean water is a mixture of gases and solids dissolved in

water

96% PURE

WATER

4% dissolved elements:

Cl, Na, Mg S, Ca, K

Salinity•total amount of solid

material dissolved in water.•number of grams of

dissolved salts in 1 kilogram of water

What two substances are the most abundant in Ocean Water?

SodiumChloride

Salts and other materials in ocean water come from:

•Volcanic activity in oceans•Erosion of land areas by rivers

•Wave action along the shoreline

Salinity Processes Affecting Salinity

• Processes that decrease salinity:

• Processes that increase salinity:

- Precipitation

- Runoff from land - Icebergs melting- Sea ice melting

- Evaporation- Formation of sea ice

Natural Processes Affecting Salinity

Salinity with depth:

Temperature of Ocean Water

•Ocean water has ability to

absorb sunlight

which heats the water

Layering of water by temperature:

Surface zone (mixed layer):

• Water temp higher at surface because of direct sunlight

• Waves and currents mix surface water and transfers heat downwards

• Extends 100-400 meters• Warmer at equator than at poles• Only place where enough light is

present to grow marine plants

Zone of rapid temperature changeWarmer water on top of layer

Colder, denser on bottom of layer

Area of very cold water that extends 1000-4000 meters

Variations in Ocean Surface Temperature

Density of Ocean Water:

•Density is the mass of a substance per unit volume

Two factors affect density

1. Salinity - Dissolved solids make ocean

water more dense than fresh water

2. Temperature- Cold water is more dense

than warm water

Most abundant gases dissolved in ocean water:

•Nitrogen (N2)

•Carbon Dioxide (CO2)

•Oxygen (O2)

• CO2 dissolves most easily

• Cold water holds more dissolved gases• Warm water holds less dissolved gases

• Think of a pot of water on the stove – what is coming out as the temperature rises???

• GASES! (oxygen)• The warmer the water, the less gas it

holds!

•The dissolved gases are recycled back into the air

•The dissolved solids do not leave, they are used by living things in the sea.

COLOR of the Ocean

•The color of the ocean is determined by the way it absorbs or reflects sunlight. Much of the sunlight penetrates the surface of the ocean and is absorbed by the water.

Blue wavelengths of light are the last color

to be absorbed

COLOR of the Ocean

•In clear ocean water, blue light can penetrate up to 100 m before being absorbed. Until it is absorbed, it is reflected and makes the upper layers of ocean water appear BLUE.

• At times it will look like other colors depending on what particles are in the water (ex. rocks, animals, etc.)

• No wavelength of light can penetrate beyond 200 meters, so beyond that

it is DARK.

Observe how upwelling occurs.

Ocean Environments

Pelagic Environment(water zone)

1.nertic zone: located above the continental shelf, has abundant sunlight, has moderate temperature, low pressure, ideal for life

•life: plankton (microscopic plants and animals), nekton (swimming forms of life), fish

2. oceanic zone: deep, open ocean beyond the continental shelf, marine life decreases with increasing depth

•life: tuna, dolphin, sargassum seaweed, little or none at deeper parts

Benthic Environment

1.intertidal zone: lies between low and high tide, unstable for marine life

•life: crabs, clams, mussels, sea anemones, seaweed

2. sublittoral zone: shallow, continuously submerged, located on shelf

•life: sea stars, brittle stars, sea lilies

•bathyal zone: begins at continental slope and extends to 4,000 meters, little or no light

•life: octopuses, sea stars, brachiopods

•abyssal zone: no light, extends 6,000m

•life: sponges, worms, sea cucumbers

•hadal zone: found in ocean trenches, deeper than 6,000m, unexplored

• life: sparse and dependant on food falling from higher levels

Marine Life Zones

The DynamicOceanCh. 16

Currents move water from place to place

There are 2 kinds of currents…

First kind of current:

1.Surface currents: move on or near surface of ocean• 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

Ocean Surface Currents

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

False-Colored Satellite Image of the Gulf Stream

Surface Circulation Ocean Currents and Climate

• When currents from low-latitude regions move into higher latitudes, they transfer heat from warmer to cooler areas on Earth.

• As cold water currents travel toward the equator, they help moderate the warm temperatures of adjacent land areas.

Upwelling

• the rise of cold water from deeper layers to replace warmer surface water.

• brings greater concentrations of dissolved nutrients, such as nitrates and phosphates, to the ocean surface.

Effects of Upwelling

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.

Conveyor Belt Model

Wave Generating forces

•WIND•TIDES•Sometimes Earthquakes

Features of a wave

CREST

TROUGH

WAVE HEIGHT

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

4 sec

Observe an animation of wave motion.

Height of wind-formed waves depends on 3 things…

1. Length of time the wind blows

2. Speed of wind

3. FETCH: length of open water over which the wind blows in a single direction

Anatomy of a Wave

Swells

• Group of long, rolling waves all about the same size

• Come at regular intervals

• 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.

Breaking Waves

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

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.