Topography of the Ocean

H.M.S. Challenger

•Topography refers to the shapes of the

ocean crust.•In this session you will learn the different

surface features of the ocean floor along with their names.

•Describe the various physiological features associated with the ocean basins.

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What factors affect the topography of the Earth’s crust after its formation?

Natural Factors Artificial Factors

• Moving Air▫ Wind

Moves particles too▫ Tornadoes

• Moving Water▫ Rain (storms)▫ Flooding▫ Wave action▫ Currents

• Geologic Factors Rift Valleys▫ Earthquakes Mountain Building▫ Volcanoes Subduction Zones

• Human Activity▫ Agriculture

Land Management Land Sculpting

▫ Industrial Mining/Resource

Retrieval Factories

▫ Commercial Road/Bridge Building Land Development

Housing Shopping

Earth Beneath the Sea• The H.M.S. Challenger was one of the first ships

to do extensive oceanic studies.• The echo sounder was an innovation that allowed

for a lot of research to be able to be conducted about the ocean's floor.

• Here is a problem: ▫ Sound travels 5000 ft. per second through water. ▫ It takes one second for the echo to go

from the ship and then be bounced off the bottom and return to the ship.

▫ The total distance is 5000 feet, so you know from the ship to the ocean floor it is half of that, or 2500 feet.

▫ The formula 1/2(5000)(time traveled) can be used anytime.

•The Earth’s crust can be divided into two parts:▫Continental crust▫Oceanic crust

•Ocean basins can be divided into two regions:▫continental margins▫deep ocean basins

•Continental Margin which is made up of:

▫Continental Slope▫Continental Rise▫Continental Shelf

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Features of the Deep Ocean Basin

•Abyssal Plains•Ridges•Seamounts and Guyots

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Vocabulary•Continental Margin – the part of our

continent that extends into the ocean.

▫Continental shelf – a slow drop in the ocean floor beginning at the coast line.

▫Continental Slope – starting at the outer edge of the continental shelf the continental slope drops off steeply toward the ocean floor.

▫Continental Rise – the area of the ocean floor that extends between the continental slope and the deep ocean floor.

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Continental Margins

•Made up of three distinct regions, the Continental Shelf, Continental Slope, and Continental Rise.

•Mostly made up of sediments that have been washed off of land.

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Continental Shelf•A gently sloping surface (less than one tenth

of a degree) that begins at the shore line and extends to the beginning of the Continental Slope.

Continental Shelf (continued)•It is primarily made up of sediments that have

been carried down rivers. Numerous hills, terraces, canyons The width of the Continental Shelf varies.

Scientists claim the average width is about 65 km.Submerged part of the continentLocally cut by canyons formed by currents and

moving sediment

Submarine Canyons and Turbidity Currents

Submarine canyons, steep walled underwater valleys, are created by turbidity currents. Click on the links to learn more about them.

Continental Slope•A fairly steep drop that separates the

Continental Shelf from the Continental Rise.▫Between the shelf and the floor and deep

ocean▫Boundary between continental and oceanic

crust•Slopes an average of 2-3 degrees

▫50 degrees off volcanic islands (much steeper!)

•It is made up of the same sediments as the Continental Shelf.

Continental Rise •Less steep than Continental Slopes.• Made of sediment deposited at the boundary between the continental slope and the abyssal plain. •The width of the Continental Rise ranges from a few kilometers to hundreds of kilometers.

The Ocean Basin Floor• 30% of the Earth's surface are made up by

these landforms:▫Deep ocean trenches, where 2 converging plates

meet, are the deepest regions of Earth. The Marianas trench can reach up to 36,000 ft. deep.

▫Abyssal plains are very flat regions made of the sediment carried by turbidity currents.

▫Seamounts are isolated volcanic peaks made by hotspots, like Hawaii. Others are near ocean ridges. Others emerge as land, like St. Helena.

A Deep Ocean Trench

Abyssal Plain

Flat, deep ocean floor.

Depth may be 3,000–6,000 m or more

Thick accumulations of sediment

The Topography of an Abyssal Plain

Location of some Seamounts around the globe

Vocabulary (continued)

•Ridges – the ocean floor has ocean basins in it. Each basin has mountain ranges just like the mountain ranges on land. Underwater mountain ranges form ridges that look like long peaks.

•Seamounts – volcanic mountains that rise more than 1,000 meters above the ocean floor. Hawaii is a seamount.

•Guyots – volcanic mountains that have been flattened by wave action and now are totally underwater.

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Mid Ocean Ridges• This is where sea floor

spreading occurs, and new crust is formed.

• These regions make up to 20% of the Earth's surface▫They run a course of

40,000 miles around the Earth that looks like a baseball seam.

• Click here to learn about the Mid-Atlantic Ridge (below, the MAR is on land in Iceland)

Undersea Volcanoes Thick, black smoke billowed miles into the sky

Scorching, red lava oozed from a turbulent sea

Molten lava hardened into pumice and cinder

Island of Surtsey emerged nearIceland, 425 feet below the ocean

Seamounts

• Seamounts and Guyots are both individual volcanic mountains on the ocean floor • Distinct because seamounts tend to be circular or conical •The difference between seamounts and guyots Guyots have been flattened and are below the ocean surface. •Some seamounts do not reach the ocean surface either.

Guyot

Flat-topped seamount rising from ocean floor like a volcano but planed off on top and covered by appreciable water depth.

Guyot Formation

Coral Reefs and Atolls•Coral reefs are made of skeletal remains

from coral polyps and algaes.

•They live in warm waters, above 75 degrees F anually.

• The H.M.S. Beagle expedition did research on atolls and their locations.

• Atolls are islands made out of coral.

Atolls•A coral reef that formed around an undersea

volcano which has since been eroded by wind and waves.

Resources

•Plate Tectonics