CHAPTER 2UNDERSEA LANDSCAPES

CHAPTER 2UNDERSEA LANDSCAPES

Until the 20th century, most knowledgeof the ocean floor came from heaving alead weight overboard with a hemp ropeand looking at the muds, weeds, oozes,and sediments retrieved.

Until the 20th century, most knowledgeof the ocean floor came from heaving alead weight overboard with a hemp ropeand looking at the muds, weeds, oozes,and sediments retrieved.

WeightWeight

Sigsbee Sounding Machine 1875

This became the basic model for the next 50 years

Sigsbee Sounding Machine 1875

This became the basic model for the next 50 years

Depth SoundingsDepth Soundings

Echo Sounder(sends signal-listens for echo)

Echo Sounder(sends signal-listens for echo)

World War I efforts to combat Germansuccesses with submarines led to: World War I efforts to combat Germansuccesses with submarines led to:

Hydrophone(listens passively)Hydrophone(listens passively)

A device for measuring depth of water by sending sound wavesdown from the surface and recordingthe time until the echo returns fromthe bottom

A device for measuring depth of water by sending sound wavesdown from the surface and recordingthe time until the echo returns fromthe bottom

Echo SounderEcho Sounder

Searching for submarines in the NorthAtlantic led to the realization of thediverse ocean floor geography.Intense effort to chart the ocean floorcommenced and continues today.

Searching for submarines in the NorthAtlantic led to the realization of thediverse ocean floor geography.Intense effort to chart the ocean floorcommenced and continues today.

The differences in elevation andslope between the higher andlower parts of the land surface ofa given area

The differences in elevation andslope between the higher andlower parts of the land surface ofa given area

Relief (of the Earth)Relief (of the Earth)

Graphic representation on a mapof the surface features of a placeor region, indicating their relativepositions and elevations

Graphic representation on a mapof the surface features of a placeor region, indicating their relativepositions and elevations

TopographyTopography

Contour LinesContour Lines~ Lines provide elevations~ Spacing indicates relative slopes~ Lines provide elevations~ Spacing indicates relative slopes

Earth’s Two Main Levels of ReliefEarth’s Two Main Levels of Relief

ContinentsContinents

Deep Ocean FloorDeep Ocean Floor

DEEP OCEAN FLOORDEEP OCEAN FLOOR

Also known as:

~ Deep sea

~ Deep ocean basin

~ Abyss

Also known as:

~ Deep sea

~ Deep ocean basin

~ Abyss

Depth Soundings

~ Described in terms of its individual features

Depth Soundings

~ Described in terms of its individual features

TrenchTrenchRidgesRidges

FractureFracture

RidgeRidge

CanyonCanyon

SeamountSeamountGuyotGuyot

IslandIsland

AbyssalPlainAbyssalPlain

Earth

71% covered bywater but onlytwo-thirds is deepoceanic basin

Earth

71% covered bywater but onlytwo-thirds is deepoceanic basin

Average depth ~ 12,000± feet (2.5 miles)Some trenches ~ 37,000+ feet (7 miles)Average depth ~ 12,000± feet (2.5 miles)Some trenches ~ 37,000+ feet (7 miles)

(Note: two ocean ridges & one rift valley)(Note: two ocean ridges & one rift valley)

Echo sounders measure the time it takes a sound pulse to travel to theocean floor and return. The deeperthe floor, the longer the return.

Echo sounders measure the time it takes a sound pulse to travel to theocean floor and return. The deeperthe floor, the longer the return.

Sound travel averages 4,800 ft/sec inwater. If an echo return takes 2 seconds,it traveled 9,600 feet. Since it is a roundtrip, the depth is 4,800 feet.

Sound travel averages 4,800 ft/sec inwater. If an echo return takes 2 seconds,it traveled 9,600 feet. Since it is a roundtrip, the depth is 4,800 feet.

You transmitted a sound in water and the echo returned in 5 seconds.

a. How far did the sound travel?

b. How deep is the ocean floor?

You transmitted a sound in water and the echo returned in 5 seconds.

a. How far did the sound travel?

b. How deep is the ocean floor?

You transmitted a sound in water and the echo returned in 5 seconds.

a. How far did the sound travel?

b. How deep is the ocean floor?

You transmitted a sound in water and the echo returned in 5 seconds.

a. How far did the sound travel?

b. How deep is the ocean floor?

The sound traveled 24,000 feet (4,800 x 5)The sound traveled 24,000 feet (4,800 x 5)

The ocean floor is at 12,000 feet(to floor and back) (24,000 ÷ 2)The ocean floor is at 12,000 feet(to floor and back) (24,000 ÷ 2)

Ocean Floor - Three Distinct AreasOcean Floor - Three Distinct Areas

The relatively shallow (up to 200meters), submerged border of acontinent that slopes graduallyand extends to a point of steeperdescent to the ocean floor

The relatively shallow (up to 200meters), submerged border of acontinent that slopes graduallyand extends to a point of steeperdescent to the ocean floor

Continental ShelfContinental Shelf

Most maritime nations have agreed that the continental shelf is a part of the land out to a depth of 200 meters (656 feet).

Most maritime nations have agreed that the continental shelf is a part of the land out to a depth of 200 meters (656 feet).

ShelfShelf

LandLand

North Carolinaabout 75 milesNorth Carolinaabout 75 miles

Continental shelves drop off at 7 to 10 feet per mile and average about 42 miles in width.

Continental shelves drop off at 7 to 10 feet per mile and average about 42 miles in width.

ShelfShelf

LandLand

ShelfShelf

LandLand

Californiaunder 1 mile

Californiaunder 1 mile

ShelfShelfLandLand

Some areas of the world have virtually no continental shelf as the oceanic plate subducts below a continental plate.

Some areas of the world have virtually no continental shelf as the oceanic plate subducts below a continental plate.

JapanJapan

PeruPeru

OmanOman

Ganges RiverBasin

Ganges RiverBasin

Tapi RiverBasin

Tapi RiverBasin

Indus RiverBasin

Indus RiverBasin

Coarse sand is the most common.Coarse sand is the most common.

Sediment such asrocks, sand, mud,

silt, clay, andgravel may

cover shelves.

Sediment such asrocks, sand, mud,

silt, clay, andgravel may

cover shelves.

Shelves maynot alwayshave a gradualslope.

Shelves maynot alwayshave a gradualslope.

The sunlit continental shelves provide food, fuel, and minerals.

The sunlit continental shelves provide food, fuel, and minerals.

Most food, oil, and mineral explorationsare on continental shelves, the areamost liable for human conflicts.

Most food, oil, and mineral explorationsare on continental shelves, the areamost liable for human conflicts.

Continental SlopeContinental Slope

Regardless of the distance from land,at some point theshelf suddenlydrops (slopes) tothe ocean floor.

Regardless of the distance from land,at some point theshelf suddenlydrops (slopes) tothe ocean floor.

FloorFloor

ShelfShelf

LandLand

The steep descent of the seabedfrom the continental shelf to theabyssal zone

The steep descent of the seabedfrom the continental shelf to theabyssal zone

Continental SlopeContinental Slope

Continental slopes descend 100 to 500 feet per mile, flattening out near the floor.

This is where the Earth’s continental crust (granitic material) meets the oceanic crust (basaltic material + sediment).

Continental slopes descend 100 to 500 feet per mile, flattening out near the floor.

This is where the Earth’s continental crust (granitic material) meets the oceanic crust (basaltic material + sediment).

Granitic Rock:~hard, speckled whitish or gray color~rough appearance~magma cooled slowly under the Earth’s surface (intrusive)~most common rock exposed on surface

Granitic Rock:~hard, speckled whitish or gray color~rough appearance~magma cooled slowly under the Earth’s surface (intrusive)~most common rock exposed on surface

Basaltic Rock:~hard, dark color~smooth to glassy appearance~lava cooled rapidly above the Earth’s surface (extrusive)~most common rock on Earth’s crust, covering the oceanic crust’s floor

Basaltic Rock:~hard, dark color~smooth to glassy appearance~lava cooled rapidly above the Earth’s surface (extrusive)~most common rock on Earth’s crust, covering the oceanic crust’s floor

GraniteGranite

SlopeSlope

Basalt+ sedimentBasalt+ sediment

If continental slope meets oceanic crustat subduction zone:If continental slope meets oceanic crustat subduction zone:

Granite is lighter relative to Basalt and rises to mountainous heights, often with volcanic activity created by the intense pressures.

Granite is lighter relative to Basalt and rises to mountainous heights, often with volcanic activity created by the intense pressures.

Deep Ocean Floor• A bleak and uncomfortable world for humans

• No light

• No plant life

• Extreme pressure

• Cold

• Sediments - mud, clay, sand, gravel

~ Andes Mountains~ Peru-Chile Trench8-mile descent in less than 100 miles

~ Andes Mountains~ Peru-Chile Trench8-mile descent in less than 100 miles

PERUPERU

CHILECHILE

Submarinecanyons,cliffs, valleys,terraces,plateaus, anddrop-offs ofseveralthousand offeet.

Submarinecanyons,cliffs, valleys,terraces,plateaus, anddrop-offs ofseveralthousand offeet.

Continental slope features are similar tocontinental surface features but on alarger scale. Some of the features are:

Continental slope features are similar tocontinental surface features but on alarger scale. Some of the features are:

A deep underwater valley withsteep sidesA deep underwater valley withsteep sides

Submarine CanyonSubmarine Canyon

A nearly level strip of land with a more or less abrupt descent along the margin of the sea, a lake, or a river

A nearly level strip of land with a more or less abrupt descent along the margin of the sea, a lake, or a river

TerraceTerrace

Submarine canyons are often carvedout by past glaciers, tidal currents,other underwater currents, andlandslides.

Submarine canyons are often carvedout by past glaciers, tidal currents,other underwater currents, andlandslides.

Continental SlopesContinental Slopes

Rapidly moving underwater currentscalled turbidity currents, carry debrisand sediments that scour the canyonwalls much like river or wind erosiondoes on continental surfaces.

Rapidly moving underwater currentscalled turbidity currents, carry debrisand sediments that scour the canyonwalls much like river or wind erosiondoes on continental surfaces.

Continental SlopesContinental Slopes

Larger than Arizona’s Grand Canyon, New York’s Submarine Hudson Canyon extends from depths of 300 feet to some7,000 feet, 150 miles off shore.

Larger than Arizona’s Grand Canyon, New York’s Submarine Hudson Canyon extends from depths of 300 feet to some7,000 feet, 150 miles off shore.

Continental SlopeContinental Slope

New JerseyNew Jersey

Hudson CanyonHudson Canyon

Long IslandLong Island

HudsonRiverHudsonRiver

AbyssAbyss

The Hudson River deposits anenormous plain of mud calleda submarine fan.

The Hudson River deposits anenormous plain of mud calleda submarine fan.

Mud, silt, and othersediment depositedwhen rivers emptyinto the ocean

Sometimes extendinghundreds of miles outto sea

Mud, silt, and othersediment depositedwhen rivers emptyinto the ocean

Sometimes extendinghundreds of miles outto sea

Submarine FanSubmarine Fan

Mississippi RiverMississippi RiverIndusIndus

GangesGanges

The world’s great rivers extend similarfans hundreds of miles out to sea.The world’s great rivers extend similarfans hundreds of miles out to sea.

Ganges River DeltaGanges River Delta

Indus River DeltaIndus River DeltaMississippiRiver DeltaMississippiRiver Delta

Submarine fans extending hundreds of miles may also deposit enough sediment to create deltas above the surface.

Submarine fans extending hundreds of miles may also deposit enough sediment to create deltas above the surface.

The deep ocean floor begins at the bottom of the continental slope and extends seaward as the true bottom.

The deep ocean floor begins at the bottom of the continental slope and extends seaward as the true bottom.

Where turbidity currents depositenough sediment at the base of thecontinental slope to change angle ofthe slope.

Where turbidity currents depositenough sediment at the base of thecontinental slope to change angle ofthe slope.

Continental RiseContinental Rise

The deep ocean floor covers one-thirdof the Atlantic and Indian Oceans, andthree-quarters of the Pacific Ocean.

The deep ocean floor covers one-thirdof the Atlantic and Indian Oceans, andthree-quarters of the Pacific Ocean.

PacificOceanPacificOcean

AtlanticOcean

AtlanticOcean

IndianOceanIndianOcean

Most of the Pacific deep ocean basin consists of rolling hills, while plains are widespread in the Atlantic.

Most of the Pacific deep ocean basin consists of rolling hills, while plains are widespread in the Atlantic.

PacificOceanEast of Japan

PacificOceanEast of Japan

Atlantic OceanEast of United States

Atlantic OceanEast of United States

Turbidity currents flow throughconnecting canyons and channels carrying land sediment.

Heavier sediments create the rise,lighter sediments settle on the plains.

Turbidity currents flow throughconnecting canyons and channels carrying land sediment.

Heavier sediments create the rise,lighter sediments settle on the plains.

Atlantic OceanEast of Canada

Atlantic OceanEast of Canada

Every deep ocean has impressive mountain ranges called ridges. TheMid-Atlantic Ridge soars more than6,000 feet.

Every deep ocean has impressive mountain ranges called ridges. TheMid-Atlantic Ridge soars more than6,000 feet.

Many underwater earthquakes occur in a rift running down the ridge's centerline.Many underwater earthquakes occur in a rift running down the ridge's centerline.

Mid-Ocean RidgeMid-Ocean Ridge

Major plate margins abutthe Mid-Ocean RidgeMajor plate margins abutthe Mid-Ocean Ridge

Almost all of the small Pacific Islandsare tops of former volcanic mountainsand true oceanic islands. They did notbreak away from continents.

Almost all of the small Pacific Islandsare tops of former volcanic mountainsand true oceanic islands. They did notbreak away from continents.

The surface remnant of a volcanic peakthat eroded or sank is known as anatoll. An old crater’s center filled withwater is a lagoon.

The surface remnant of a volcanic peakthat eroded or sank is known as anatoll. An old crater’s center filled withwater is a lagoon.

SeamountSeamount

In some cases, coralislands subside anddisappear beneaththe sea surface,leaving a peakedseamount.

Found in all oceansbut most commonin the Pacific.

In some cases, coralislands subside anddisappear beneaththe sea surface,leaving a peakedseamount.

Found in all oceansbut most commonin the Pacific.

An underwater mountain risingfrom the ocean floor and havinga flat topped or peaked summitbelow the surface of the sea

An underwater mountain risingfrom the ocean floor and havinga flat topped or peaked summitbelow the surface of the sea

SeamountSeamount

In other cases,volcanic activitythat does not reach the seasurface canalso leave anunderwatermountaincalled a seamount.

In other cases,volcanic activitythat does not reach the seasurface canalso leave anunderwatermountaincalled a seamount.

Accurate seamount location and charting is critical for navigation.

In January 2005, SSN San Francisco (SSN 711) collided with just such a seamount.

Accurate seamount location and charting is critical for navigation.

In January 2005, SSN San Francisco (SSN 711) collided with just such a seamount.

Seamounts with flattened tops are guyots.

Guyots are found only in the Pacific.

Seamounts with flattened tops are guyots.

Guyots are found only in the Pacific.

A flat topped seamount

Guyots show evidence of having been above the surface, worn by ocean waves, and gradually subsiding under their own weight as the sea rose.

A flat topped seamount

Guyots show evidence of having been above the surface, worn by ocean waves, and gradually subsiding under their own weight as the sea rose.

GuyotGuyot

The Hawaiian Islands are part of achain created by volcanic eruption asthe Pacific Plate moves northwest.

The Hawaiian Islands are part of achain created by volcanic eruption asthe Pacific Plate moves northwest.

Southeast of the big island, Hawaii,the newest seamount is activelybuilding to be the next island.

Southeast of the big island, Hawaii,the newest seamount is activelybuilding to be the next island.

LoihiSeamountLoihiSeamount

Mauna LoaMauna Loa

KilaueaKilauea

Two of the world’s most active volcanoesare on the bigisland of Hawaii.

Two of the world’s most active volcanoesare on the bigisland of Hawaii.

High enough to have snow when dormant, Mauna Loa’s lava flow is 13,677 feet above the Pacific Ocean but more than 31,000 feet from the ocean floor.

High enough to have snow when dormant, Mauna Loa’s lava flow is 13,677 feet above the Pacific Ocean but more than 31,000 feet from the ocean floor.

Similar Volcanic Island ChainsSimilar Volcanic Island Chains

SocietyIslandsSocietyIslands

SamoanIslandsSamoanIslands

GilbertIslandsGilbertIslands

CarolineIslandsCarolineIslands

South PacificSouth Pacific

Ocean floor sediments consist of threegeneral types:

• Oozes

• Clays

• Land-derived muds

Ocean floor sediments consist of threegeneral types:

• Oozes

• Clays

• Land-derived muds

SedimentsSediments

OozesOozes

Composed of marine shells, andskeletons of minute animals,oozes are found in warm, shallower waters of the equatorial areas and the Atlantic.

Composed of marine shells, andskeletons of minute animals,oozes are found in warm, shallower waters of the equatorial areas and the Atlantic.

Volcanic, meteorite, and airborne dustsmake up the dark brown or reddish clayof the deep, cold, parts of the oceanbasin as in the North Pacific.

Volcanic, meteorite, and airborne dustsmake up the dark brown or reddish clayof the deep, cold, parts of the oceanbasin as in the North Pacific.

ClaysClays

Land-derived materials delivered byriver flow createthe muds thatempty into theoceans andspread over theabyssal plains.

Land-derived materials delivered byriver flow createthe muds thatempty into theoceans andspread over theabyssal plains.

MudsMuds

Sediment does not always remain stationary. Underwater landslides and water flow may scour sediment in some areas and deposit great thickness in others.

Sediment does not always remain stationary. Underwater landslides and water flow may scour sediment in some areas and deposit great thickness in others.

Fine sediment buildup onthe deep seabed is veryslow:

1 inch every 2,500 years.

Fine sediment buildup onthe deep seabed is veryslow:

1 inch every 2,500 years.

Volcanic eruptions spread sediments for miles. The ash and dust may circle the globe for years before falling to the Earth's surface.

Volcanic eruptions spread sediments for miles. The ash and dust may circle the globe for years before falling to the Earth's surface.

Icebergs, river and shore ice entrapDetritus, loose material (stone fragments,silt, etc.) that is worn away fromRocks that falls to the ocean floor when they melt.

Icebergs, river and shore ice entrapDetritus, loose material (stone fragments,silt, etc.) that is worn away fromRocks that falls to the ocean floor when they melt.

Mineral crystals often solidify or encrust around tiny objects on the sea bottom, forming nodules, or lumps of metal.

Mineral crystals often solidify or encrust around tiny objects on the sea bottom, forming nodules, or lumps of metal.

The most valuable nodule is onethat contains manganese, used chiefly as an alloying agent in steel to give it toughness

The most valuable nodule is onethat contains manganese, used chiefly as an alloying agent in steel to give it toughness

A grayish white, usually hardand brittle, metallic element thatresembles iron but is not magnetic

A valuable oxidizing agent

Used chiefly as an alloying agentin steel to give it toughness

A grayish white, usually hardand brittle, metallic element thatresembles iron but is not magnetic

A valuable oxidizing agent

Used chiefly as an alloying agentin steel to give it toughness

ManganeseManganese

Abundant Manganese AreasAbundant Manganese Areas

Most manganese is found at depths over 12,000 feet making retrieval difficult.Most manganese is found at depths over 12,000 feet making retrieval difficult.

Most seafloorsediment samples areobtained byusing a coringtube.

Most seafloorsediment samples areobtained byusing a coringtube.

Studying cores with tiny animal shells in the ooze and sediment provides ahistory of that part of the ocean. Fossils give clues about geological ageand temperatures of the sea.

Studying cores with tiny animal shells in the ooze and sediment provides ahistory of that part of the ocean. Fossils give clues about geological ageand temperatures of the sea.

Deep water drilling showed:

~ North Atlantic began to form 200 million years ago, South Atlantic 150 million years ago.~ Earth’s surface is made up of moving plates.

Deep water drilling showed:

~ North Atlantic began to form 200 million years ago, South Atlantic 150 million years ago.~ Earth’s surface is made up of moving plates.

A.1. A team of U.S. Navy scientistsA.1. A team of U.S. Navy scientists

Q.1. Who invented the hydrophone?Q.1. Who invented the hydrophone?

A.2. To show elevations of the Earth’s surface by using colors or numbers

A.2. To show elevations of the Earth’s surface by using colors or numbers

Q.2. What is the purpose of a relief map of the Earth’s surface?Q.2. What is the purpose of a relief map of the Earth’s surface?

A.3. 42 milesA.3. 42 miles

Q.3. The average width of the continental shelves is about how many miles from the shore line?

Q.3. The average width of the continental shelves is about how many miles from the shore line?

A.4. 2.5 miles deepA.4. 2.5 miles deep

Q.4. What is the average depth of the ocean?Q.4. What is the average depth of the ocean?

A.5. The continental shelfA.5. The continental shelf

Q.5. In what part of the ocean would you find sea vegetation?Q.5. In what part of the ocean would you find sea vegetation?

A.6. Ocean ridges are enormousmountain ranges running alongthe center of the ocean floor.

A.6. Ocean ridges are enormousmountain ranges running alongthe center of the ocean floor.

Q.6. What are ocean ridges?Q.6. What are ocean ridges?

A.7. RiftsA.7. Rifts

Q.7. The enormous cracks that are found in the ocean are referred to as what?

Q.7. The enormous cracks that are found in the ocean are referred to as what?

Q.8. What is the drop rate of the continental slope?Q.8. What is the drop rate of the continental slope?

A.8. 100 to 500 feet per mileA.8. 100 to 500 feet per mile

A.9. Oozes, clay, and land-derived mudsA.9. Oozes, clay, and land-derived muds

Q.9. What type of materials makeup the ocean floor?Q.9. What type of materials makeup the ocean floor?

A.10. The continental shelf, continental slope, and deep ocean basin

A.10. The continental shelf, continental slope, and deep ocean basin

Q.10. What are the three (3) areas the ocean floor is divided into?Q.10. What are the three (3) areas the ocean floor is divided into?

A.11. The abyssA.11. The abyss

Q.11. What is the deep ocean floor sometimes referred to?Q.11. What is the deep ocean floor sometimes referred to?

A.12. The delta of a large river in which an enormous plain of mud can be deposited hundreds of miles out to sea

A.12. The delta of a large river in which an enormous plain of mud can be deposited hundreds of miles out to sea

Q.12. What is a submarine fan?Q.12. What is a submarine fan?

A.13. Through volcanic eruptionA.13. Through volcanic eruption

Q.13. How were most of the Pacific islands formed?Q.13. How were most of the Pacific islands formed?

A.14. A flat-topped undersea mountain believed to have formed from repeated volcanic eruptions

A.14. A flat-topped undersea mountain believed to have formed from repeated volcanic eruptions

Q.14. What is a guyot, and how is it formed?Q.14. What is a guyot, and how is it formed?