Geological OceanographyOcean TopographyThe scientific

study of the origin, history, and structure of the earth

Topography is a graphic representation of the surface features

of a place or region …in this case, the ocean basins.

What do ocean basins look like?

How do we know what it looks like?

Soundings are made by sending a sound pulse into the water.

• Echosounders are attached to the hull of a ship or a towed vehicle. 

• An echosounder sends a sound pulse into the water.  The sound energy travels through the water to the ocean bottom where it is reflected back towards the source, received, and accurately measured.

Undersea structures shown by Sonar

• This surprised oceanographers who expected the ocean bottoms to be smoother, more like a bowl (deepest in the middle and getting shallower towards continents).

Features found on the seafloor

Continent Mid-ocean ridge Sea mount

Oceanic trench

Abyssal plain

Continental shelf

Central rift zoneDepth (m)

Geological Oceanography Journal Question

• http://videos.howstuffworks.com/science/sonar-videos-playlist.htm#video-30297

1. Describe how scientists find out what the ocean floor looks like?

The ocean basin: Structures1. Continental Margin: Continental Shelf

Continental SlopeContinental RiseSubmarine Canyons

2. Deep Ocean Basin: Abyssal PlainsOceanic ridges

3. Trenches4. Seamounts and Guyots5. Atolls

Submerged, outer edge of the continents.

Two types: 1. Active Margin (Pacific)

2. Passive Margin (Atlantic)

Found on the leading edge of the continent crashing into an oceanic plate.No collisions taking place, tectonic activity is minimal

Continental Shelf:

Similar to the continent (compared to the deep ocean).

They have hills, depressions, mineral and oil deposits.

In Atlantic Canada, the continental shelf holds the best fishing areas.

Submarine Canyon: on the edge of the

continental shelf• V-shaped indentations into the

continental shelf, usually ending in a fan shaped wedge of sediments.

The Gully!• Submarine canyon off Nova Scotia• Marine protected area because of the rare corals found

there• The natural gas pipeline goes right by it though!

The Gully

• This coral forms colonies up to two meters high and takes between 200 and 500 years to grow such a colony. They only grow 1.5 millimeters a year."

Bubble Gum coral

Largest reported from N.S. was 7m tall!

Deep Ocean Basin• Abyssal plains: From the

Greek meaning “without bottom”. They are flat, cold, dark, featureless expanses of sediment-covered ocean floor. They are most common in the Atlantic.

• Ocean Ridges: Mountainous chains of actively spreading ocean floor. They can rise 2km from the ocean floor and sometimes form islands such as Iceland, the Azores and Easter island.

Mid-Atlantic Ridge

Trenches• Deep gap in ocean floor,

formed by movement of plates.

• Example: Mariana Trench is 10,668 meters deep

• They are among the most active areas on Earth.

• They are the deepest areas of the Earth’s crust.

• 90% of trenches are found around the Pacific rim.

Seamounts and GuyotsBoth are undersea volcanoes that originated at a

hotspot or along a ridge Guyots once reached the surface of the ocean

and have flat, eroded topsSeamounts never reached the surface, so they have pointy tops

Atolls• A ring shaped island of coral reefs and coral

debris. These often form over sinking inactive volcanoes.

Ocean floor features:

Trenches

Mountain chains

Sea mounts

Fracture zones

Copy and complete this Chart

Ocean Structure Two – Three Key Facts

Continental Margin

Deep Ocean Basin

Trenches

Seamounts and Guyots

Atolls