6_OCE 3008_Chapter 3 Pt2

Midterm Information

• Midterm #1 Date: Tuesday, Feb 04 (two weeks from Tuesday)

• Topics Covered: Chapters 1-4

• Sample Exam Questions: Available on Webcourses Announcements

Chapter 3 - Marine Provinces

Bathymetry

• Definition: The study of ocean depths and ocean floor topography.

• Techniques Used:

  • Echo Sounding: A method for measuring the depth of water by sending a sound pulse and recording its return time.

  • Satellites: Used for global ocean topography monitoring.

• Plate Tectonics: Understand how ocean floor features are generated by processes that involve the movement of the Earth's plates.

• Sea Floor Features:

  • Continental margins

  • Deep-ocean basins

  • Mid-ocean ridge

Continental Shelf

• Definition: A flat zone extending from the shore to the shelf-slope break.

• Characteristics:

  • Shelf break: Significant slope increase occurs here (average width about 70 km; can range from meters to 1500 km).

  • Average depth at shelf break is approximately 135 meters (443 feet).

  • Geologically part of the continent with granite rock underneath.

Continental Slope

• Location: Begins at the base of the continental shelf.

• Topography: Resembles mountain ranges with high relief.

  • Shelf-slope break is 1-5 km above the base of the deep-ocean basin.

• Slope Gradient:

  • Generally steeper than the continental shelf (averages around 4°, can vary from 1° to 25°).

  • Marked by submarine canyons and greater vertical relief in regions with convergent active margins.

Submarine Canyons

• Description: Narrow, V-shaped deep valleys (e.g., Monterey Canyon).

• Characteristics:

  • Steep walls and extend to the base of the continental slope.

  • Carved by turbidity currents, not rivers (especially during low sea levels).

  • Depth typically reaches around 3500 meters (11,500 feet).

Turbidity Currents

• Definition: Underwater avalanches of mixed sediment that behave like mudflows on land.

• Trigger Factors: Seismic activity, sediment oversteepening, storms, sediment floodwaters.

• Movement: Flows downslope due to gravity, carving canyons as they move.

Continental Rise

• Location: Found at the base of passive continental margins, serving as a transition from the continental slope to the deep-ocean floor.

• Characteristics:

  • Appears fan- or lobate-shaped from above.

  • Marked by turbidite deposits from turbidity currents, indicating graded bedding.

Active Continental Margins

• Types:

  • Convergent Active Margins:

    • Features include active continental volcanoes, narrow shelf, steep slope, and offshore trench (e.g., South American coastline).

  • Transform Active Margins:

    • Characteristics: Creates rough continental shelf with relief due to transform faults (e.g., California's San Andreas Fault).

Abyssal Plains

• Definition: Large, flat, and deep-sea floor regions located between continental margins and mid-ocean ridges.

• Depth Range: Typically between 4500 m to 6000 m.

• Characteristics: Fine sediments settle over millions of years and cover seafloor irregularities.

Volcanic Features on Abyssal Plains

• Types: Seamounts (over 1 km high), tablemounts (flat-topped), and abyssal hills (under 1 km high).

• Formation Mechanism: Stretching of the crust during sea-floor formation.

Coral Reefs

• Types: Fringing, barrier, and atolls.

• Formation Process:

  • Coral reefs grow progressively in response to underlying volcanic islands sinking.

Ocean Trenches and Volcanic Arcs

• Characteristics: Form at convergent plate boundaries, including the deepest oceans like the Mariana Trench (36,161 feet deep).

• Types of Arcs:

  • Island Arcs: Forms in oceans (e.g., Japan).

  • Continental Arcs: Mountain ranges on land (e.g., Andes).

Pacific Ring of Fire

• Description: The area around the Pacific Ocean characterized by frequent earthquakes and volcanoes.

• Trench Distribution: Most ocean trenches are located along the Pacific margins, associated with subduction zones.