Chapter 3: Marine Provinces

Convergent active margins

- continental margins that are associated with oceanic-continental convergent plate boundaries. -From the land to the ocean, features include an onshore arc-shaped row of active volcanoes, then a narrow shelf, a steep slope, and an offshore trench that delineates the plate boundary -Western South America, where the Nazca Plate is being subducted beneath the South American Plate, is an example of a convergent active margin.

hypsographic curve

-A curve that displays the relative elevations of the land surface and depths of the ocean. - provides evidence of plate tectonics - reveals that 70.8% of Earth is covered by ocean

Bathymetry

-the measurement of ocean depths and the charting of the shape or topography of the ocean floor

Pillow basalt

A basalt exhibiting pillow structure. See pillow lava

Metal sulfide

A compound containing one or more metals and sulfur.

Tablemount

A conical volcanic feature on the ocean floor resembling a seamount except that it has had its top truncated to a relatively flat surface.

Active margin

A continental margin marked by a high degree of tectonic activity, such as those typical of the Pacific Rim. Types of active margins include convergent active margins (marked by plate convergence) and transform active margins (marked by transform faulting).

Passive margin

A continental margin that lacks a plate boundary and is marked by a low degree of tectonic activity, such as those typical of the Atlantic Ocean - ex.East Coast of US Features of these include the continental shelf, the continental slope, and the continental rise that extends toward the deep-ocean basins

Rift valley

A deep fracture or break, about 25 to 50 kilometers (15 to 30 miles) wide, extending along the crest of a mid-ocean ridge.

Abyssal hill province

A deep-ocean region, particularly in the Pacific Ocean/ active continental margin, where oceanic sedimentation rates are so low that abyssal plains do not form and the ocean floor is covered with abyssal hills.

Echo sounder (fathometer)

A device that transmits sound from a ship's hull to the ocean floor where it is reflected back to receivers. The speed of sound in the water is known, so the depth can be determined from the travel time of the sound signal.

Transform fault

A fault with side-to-side motion that offsets segments of a mid-ocean ridge. Oceanic transform faults occur wholly on the ocean floor, while continental transform faults occur on land. -occur between offset segments of the midocean ridge, -two plates are moving in opposite directions, which results in an abundance of earthquakes that are quite shallow

Abyssal plain

A flat depositional surface extending seaward from the continental rise or oceanic trenches. -are formed by fine particles of sediment slowly drifting onto the deep-ocean floor

Pillow lava

A general term for those lavas displaying discontinuous pillow-shaped masses (pillow structure) caused by the rapid cooling of lava as a result of underwater eruption of lava or lava flowing into water.

Continental rise

A gently sloping depositional surface at the base of the continental slope. -comprised of a huge submerged pile of debris transported by turbidity currents - is not present in active continental margins because , the steep continental slope leads directly into a deep-ocean trench. Sediment from turbidity currents accumulates in the trench.

Continental shelf

A gently sloping depositional surface extending from the low water line to the depth of a marked increase in slope around the margin of a continent or island. -It is usually flat and relatively featureless because of marine sediment deposits but can contain coastal islands, reefs, and raised banks. The underlying rock is granitic continental crust, so this is geologically part of the continent

Turbidity current

A gravity current resulting from a density increase brought about by increased water turbidity. Possibly initiated by some sudden force such as an earthquake, the turbid mass continues under the force of gravity down a submarine slope. - are thought to be responsible for carving submarine canyons

Continental borderland

A highly irregular portion of the continental margin that is submerged beneath the ocean and is characterized by depths greater than those characteristic of the continental shelf. ((islands, shallow banks, and deep basins) - occurs at transform active margins such as at California

White smoker

A hydrothermal vent feature similar to a black smoker but emitting water of a lower temperature that is white in color - have water temperatures from 30° to 350°C (86° to 662°F) and emit water that is white because of the presence of various light-colored compounds, including barium sulfide.

Warm-water vent

A hydrothermal vent feature that generally emits water that is clear in color.

Black smoker

A hydrothermal vent on the ocean floor that emits a black cloud of hot water filled with dissolved metal particles. -have water temperatures above 350°C (662°F) and emit water that is black because of the presence of dark-colored metal sulfides, including iron, nickel, copper, and zinc

Deep-sea fan

A large fan-shaped deposit commonly found on the continental rise seaward of such sediment-laden rivers as the Amazon, Indus, or Ganges-Brahmaputra. Also known as a submarine fan. -create the continental rise when they merge together along the base of the continental slope

Island arc

A linear arrangement of islands, many of which are volcanic, usually curved so that the concave side faces a sea separating the islands from a continent. The convex side faces the open ocean and is bounded by a deep-ocean trench.

Mid-ocean ridge

A linear, volcanic mountain range that extends through all the major oceans, rising 1 to 3 kilometers (0.6 to 2 miles) above the deep-ocean basins. Averaging 1500 kilometers (930 miles) in width, rift valleys are common along the central axis. Source of new oceanic crustal material.

Trench

A long, narrow, and deep depression on the ocean floor with relatively steep sides that is caused by plate convergence; often referred to as an ocean trench.

Sounding

A measured depth of water beneath a ship.

Oceanic rise

A portion of the global mid-ocean ridge system that is characterized by fast spreading and gentle slopes.

Oceanic ridge

A portion of the global mid-ocean ridge system that is characterized by slow spreading and steep slopes.

Seismic reflection profile

A profile view of the structure beneath the sea floor produced by the energy generated from explosions or air guns. - sounds reflect off of reflect off the boundaries between different rock or sediment layers -have applications in mineral and petroleum exploration

Continental slope

A relatively steeply sloping surface lying seaward of the continental shelf. - average slope is 4 degrees

Turbidite deposit

A sediment or rock formed from sediment deposited by turbidity currents characterized by both horizontally and vertically graded bedding.

Ping

A sharp, high-pitched sound made by the transmitting device of many sonar systems. - produces echoes when it bounces off any density difference, such as marine organisms or the ocean floor

Submarine canyon

A steep, V-shaped canyon cut into the continental shelf or slope.

Fathom (fm)

A unit of depth in the ocean, commonly used in countries using the English system of units. It is equal to 1.83 meters (6 feet).

Abyssal hill

A volcanic peak rising less than 1 kilometer (0.6 mile) above the ocean floor. Also known as a seaknoll. -are created by stretching of crust during the creation of new sea floor at the mid-ocean ridge. - During ice ages when sea level is lowered, there is less water and therefore less weight overlying the mid-ocean ridge. This reduction in pressure allows the mantle to produce more melt, resulting in an increased number of these

Sonar

An acronym for sound navigation and ranging, a method that uses sound to determine the distance of objects in the ocean.

Volcanic arc

An arc-shaped row of active volcanoes directly above a subduction zone. Can occur as a row of islands (island arc) or mountains on land (continental arc).

Continental arc

An arc-shaped row of active volcanoes produced by subduction that occurs along convergent active continental margins.

Precision depth recorder (PDR)

An early type of sonar device that was developed in the 1950s.

Fracture zone

An extensive linear zone of unusually irregular topography of the ocean floor, characterized by large seamounts, steep-sided or asymmetrical ridges, troughs, or long, steep slopes. -Usually represents ancient, inactive transform fault zones. -occur beyond the offset segments of the midocean ridge. -separate a single plate moving in the same direction

Pacific Ring of Fire

An extensive zone of volcanic and seismic activity that coincides roughly with the borders of the Pacific Ocean.

Seamount

An individual volcanic peak extending over 1kilometer (3300 feet) above the surrounding ocean floor but below ocean surface

Deep-ocean basin

Areas of the ocean floor that have deep water, are far from land, and are underlain by basaltic crust

- At passive margins shelf is wider - At active margins shelf is narrower and shelf-break is closer to shore

How does the size of the continental shelf vary with type of continental margin?

- few abyssal plains are found near active continental margins because the deep-ocean trenches found on the convergent active margins of the Pacific Ocean prevent sediment from moving past the continental slope. In essence, the trenches act like a gutter that traps sediment transported off the land by turbidity currents. - there are more on passive margins because turbidity currents travel directly down the continental margin and deposit sediment on the abyssal plains

How does the type of continental margin influence the distribution of abyssal plains?

Hydrothermal vent

Ocean water that percolates down through fractures in recently formed ocean floor is heated by underlying magma and surfaces again through these vents. They are usually located near the axis of spreading along the mid-ocean ridge.

Graded bedding

Stratification in which each layer displays a decrease in grain size from bottom to top. - characteristic of turbidite deposits

Shelf break

The depth at which the gentle slope of the continental shelf steepens appreciably. It marks the boundary between the continental shelf and continental rise.

Seabeam

The first multibeam echo sounder. -instruments emit multiple beams of sound waves, which are reflected off the ocean floor. As the sound waves bounce back with different strengths and timing, computers analyze these differences to determine the depth and shape of the sea floor and whether the bottom is rock, sand, or mud - Because its beams of sound spread out with depth, multibeam systems have resolution limitations in deep water

Suspension settling

The process by which fine-grained material that is being suspended in the water column slowly accumulates on the sea floor.

Continental margin

The submerged area next to a continent comprising the continental shelf, continental slope, and continental rise.

Precipitate

To cause a solid substance to be separated from a solution, usually due to a change in physical or chemical conditions.

Continental Margins, Deep-Ocean basins, and Mid-Ocean ridges

What 3 main provinces can the ocean be divided into?

(1) islands associated with volcanic activity along the mid-ocean ridge (such as Ascension Island along the Mid-Atlantic Ridge); (2) islands associated with hotspots (such as the Hawaiian Islands in the Pacific Ocean); and (3) islands that are island arcs and associated with convergent plate boundaries (such as the Japanese archipelago in the Pacific Ocean;

What are the three types of oceanic islands?

side-scan sonar -is towed behind a survey ship and can be lowered to just above the ocean floor to produce a detailed strip map of ocean floor bathymetry

What instrument should be used to measure the depth of the ocean floor for deep water or for areas where a detailed survey is required?

-In fact, more than 20,000 volcanic peaks are known to exist on the Pacific sea floor, including the recently discovered largest single volcano on Earth, Tamu Massif, which is comparable in size to the largest known volcano in our solar system, Olympus Mons on Mars.

What is the largest volcano on Earth?

HMS Challenger

What was the name of the first ship whose measurements indicated that the ocean floor had relief( variation in elevation)?

-In fact, the deepest point on Earth's surface—11,022 meters (36,161 feet)—is found in the Challenger Deep area of the Mariana Trench

Where is the deepest part of the ocean found?

-transform faults occur for two reasons: first, to accommodate spreading of a linear ridge system on a spherical Earth and, second, because different segments of the mid-ocean ridge spread apart at different rates

Why are mid-ocean ridges cut by transform faults?

Megaplume

a discharge of warm, mineral-rich water that is lower in density than the surrounding seawater and thus rises to the surface caused by an underwater volcanic eruption

Transform active margin

continental margins that are associated with transform plate boundaries. At these locations, there are usually offshore faults that parallel the main transform plate boundary fault and create linear islands, banks (shallowly submerged areas), and deep basins close to shore. ex. Coastal California along the San Andreas Fault