OCE1001 Ch 3 Marine Provinces

Of the following techniques, which one(s) can be used to map the sea floor?

direct visitation of the sea floor, recording many depths using a long cable, sending sound through water (sonar) , using satellites to measure the sea surface

Which of the following is an example of an active continental margin?

west coast of Chile, west coast of the United States

Where along a mid-ocean ridge system would you expect the most earthquakes to occur?

along the ridge axis and along transform faults that offset the axis of the ridge

Where would you expect to find graded bedding?

deep-sea fans

Which of the following feature(s) is/are associated with the mid-ocean ridge?

basalt volcanism and pillow lavas, hydrothermal vents, a central rift valley, volcanoes

The measurement of ocean depth and the charting of seafloor topography is called __________.

bathymetry (Bathymetry is sometimes referred to as "underwater topography.")

What are turbidity currents?

dense mixtures of sand, mud, and other debris that move at high speeds down submarine canyons

Trenches are typically associated with ________.

convergent continental margins (A trench is formed when oceanic crust is subducted under continental crust.)

Most large ocean floor features owe their origins to _________.

plate tectonic processes (Ridges, trenches, seamounts, etc. result from plate interactions and/or plate movements over hotspots)

What is/are the advantage(s) of a multibeam sounder compared to traditional echo sounding?

provides information about seafloor composition, more detailed, more accurate, provides a swath of measurements with each sweep of the seafloor

What would you look for as evidence that a rock layer formed from materials deposited by ancient turbidity currents?

repeated sequences of graded bedding that begin as coarse material and become finer upward

Measurement of ocean floor bathymetry from satellites relies on ___________.

sea surface elevation, which varies depending on the shape of the underlying sea floor

What feature(s) can be recognized using multibeam sonar?

tablemount, shipwreck, seamount, ridge axis

The majority of ocean trenches are associated with ___________.

the Pacific Ring of Fire, subduction zones and associated faults, very deep ocean water depths, narrow or no continental shelves, volcanic arcs and active continental margins

What is bathymetry?

the study of the depth of the ocean

What is turbidity?

suspended sediment

Which of the following is a difference between passive and active continental margins?

Convergent active margins will have a steep continental slope, whereas passive margins will have a more gradual slope.

Recall that the speed of sound in water is 1507 meters/second (4944 feet/second). If a sonar sounding had a total travel time of 5 seconds, what is the water depth?

3767.5 meters (12,360.5 feet)

The greatest proportion of Earth's surface lies in this elevation/depth interval.

4,000 - 5,000 m below sea level (This includes most of the area of the ocean basins)

A ship's fathometer (an echo sounder) transmits a sound pulse and records the return of an echo 7.4 seconds later. If the speed of sound in water is 1,500 m/second, what is the water depth in meters?

5,550 meters (Remember that the sound has to travel down and back.)

What techniques are used to determine ocean bathymetry?

Bathymetry is the measurement of ocean depths and the charting of ocean floor topography. The varies bathymetry of the ocean floor was first determined using soundings to measure water depth. Later, the development of the echo sounder gave ocean scientists a more detailed representation of the sea floor. Today, much of our knowledge of the ocean floor has been obtained using various multibeam echo sounders or side-scan sonar instruments (to make detailed bathymetric maps of a small area of the ocean floor), satellite measurement of the ocean surface (to produce maps of the world ocean floor), and seismic reflection profiles (to examine Earth structure beneath the sea floor).

Why is Greenland currently an area of active seafloor research?

Coastal water depths surrounding Greenland have not yet been well documented, Deep ocean currents cause coastal glaciers to melt

What features are associated with a passive continental margin?

Flat coastal terrain, continental rise

Of the following statements about mapping the ocean floor, which is/are true?

Multibeam surveys from ships produce very detailed maps of the sea floor, Only about 20% of the sea floor has been accurately mapped in detail, Measurements of sea surface elevation by satellites are used to produce maps of the sea floor.

Which of the following statements is/are true regarding offsets in the mid-ocean ridge system?

Offsets include both inactive and active segments, Segments of a mid-ocean ridge are initially aligned. Transform faults form when different segments spread at different rates, Offsets occur where two plates slide past each other.

What features exist on continental margins?

Passive continental margins are not associated with any plate boundaries. Features of passive margins include, from the shore outward, the continental shelf, the continental slope, and the continental rise. The continental shelf is generally shallow, low relief, and gently sloping; it can also contain varios features such as coastal islands, reefs, and banks. The boundary between the continental slope and the continental shelf is marked by an increase in slope that occurs at the shelf break. Cutting deep into the continental slopes are submarine canyons, which resemble canyons on land but are created by erosive turbidity currents. Turbitdity currents deposit their sediment load at the base of the continental slope, creating deep-sea fans that merge to produce a gently sloping continental rise. The deposits from turbidity currents (called turbidite deposits) have characteristic sequences of graded bedding. Active margins have similar features although they are modified by their associated plate boundary. Active continental margins have some features in common with passive margins, although they are modified by their associated plate boundary (either convergent or transform). Active continental margins are associated with a high degree of tectonic activity such as earthquakes, volcanoes, tall mountains, and in some cases deep trenches located close to shore.

Which of the following statements is/are true regarding submarine canyons and turbidity currents?

Submarine canyons cut into the continental slope of passive and active continental margins, Deep-sea fans are composed of numerous layers of turbidite deposits that can reach thicknesses of 1 to 2 kilometers (.6 to 1.2 miles).

What features exist in the deep-ocean basins?

The continental rises gradually become flat, extensive, deep-ocean abyssal plains, which form by suspension settling of fine sediment. Poking through the sediment cover of the abyssal plains are numerous volcanic peaks, including volcanic islands, seamounts, tablemounts, and abyssal hills. In the Pacific Ocean, where sedimentation rates are low, abyssal plains are not extensively developed, and abyssal hill provinces cover broad expanses of ocean floor. Along the margins of many continents-especially those around the Pacific Ring of Fire-are deep linear scars called ocean trenches that are associated with convergent plate boundaries and volcanic arcs.

Of the following statements about Earth's hypsographic curve, which is/are true?

The hypsographic curve shows that the average depth of the ocean is about four times the average height of the continents, The hypsographic curve shows that a majority of the exposed land is below 1 kilometer in elevation, The hypsographic curve shows that a majority of the ocean floor is more than 4 kilometers deep, The hypsographic curve shows the percentage of Earth's surface area that is covered by ocean waters.

What features exist along the mid-ocean ridge?

The mid-ocean ridge is a continuous mountain range that winds through all ocean basins and is entirely volcanic in origin. Common features associated with the mid-ocean ridge include a central rift valley, faults and fissures, seamounts, pillow basalts, hydrothermal vents, deposits of metal sulfides, and unusual life forms. Segments of the mid-ocean ridge are either oceanic ridges if steep with rugged slopes (indicative of slow sea floor spreading) or oceanic rises if sloped gently and less rugged (indicative of fast spreading). Long linear zones of weakness-fracture zones and transform faults-cut across vast distances of ocean floor and offset the axes of the mid-ocean ridge. Fracture zones and transform faults are differentiated from one another based on the direction of movement across the feature. Fracture zones (an intraplate feature) have movement in the same direction, while transform faults (a transform plate boundary) have movement in opposite directions.

What effect do turbidity currents have on the continental slope?

Turbidity currents are erosive to the continental slope and, as a result, carve out submarine canyons.

Of the following statements about turbidity currents, which is/are true?

Turbidity currents are highly erosive and carve submarine canyons, Turbidity currents are episodic events (they don't occur all the time, but only every so often, like a flash flood), Turbidity currents move sediment down the continental shelf and the continental slope to be deposited on the continental rise, The material carried by turbidity currents is what builds deep-sea fans.

How do turbidity currents affect canyons?

Turbidity currents erode material from canyons as currents move downslope.

Of the following items, which is/are associated with a passive continental margin?

a wide continental shelf, a continental rise

An oceanographic vessel is mapping a section of the ocean floor stretching for tens of miles in all directions. The seafloor is extremely flat, with a slope of less than one degree, and the water depth is about 4,500 meters. The area being mapped is most likely a(n) __________.

abyssal plain (Abyssal plains are large, very flat areas of the ocean floor that are covered with sediments.)

Sediments deposited by the process of suspension settling produce the majority of sediment found on ___________.

abyssal plains

What is the characteristic layering of an individual turbidity current deposit called?

graded bedding - Graded bedding is the characteristic layering of an individual turbidity current deposit from big pieces on the bottom to progressively finer pieces on top.

What types of deposits do turbidity currents leave in alluvial fans?

graded bedding that begins as coarse material and becomes finer upward

How often do turbidity currents occur?

infrequently

What processes influence the shape and features of continental shelves?

large fluctuations in sea level over geologic time, major climate changes, such as ice ages, tectonic activity produced by offshore faults, trench formation at convergent boundaries

Graded bedding provides evidence that __________.

large, heavy particles settle out first as current velocity decreases (That is why the large particles are found at the bottom of each sequence.)

In comparison with other ocean basins, major sedimentary features such as continental rises and abyssal plains are relatively rare in the Pacific. The primary reason for their scarcity in the Pacific is that __________.

sediment is trapped within the trenches of the convergent plate boundaries ringing the Pacific (Sediments tend to accumulate and are eventually subducted in trenches. Most sediment in the Pacific does not get past the trenches and into the ocean basins.)

The reason the deposit on the bottom forms the way it does is a result of __________.

settling velocity - The deposit on the bottom forms as a result of settling velocity (the speed at which objects sink through water), not density stratification (which is a function of density differences).

Where a mid-ocean ridge is offset, the linear feature connecting and between the crests of the ridge segments is called a __________.

transform fault (Transform faults mark the active part of the offset, with opposing motion on opposite sides of the faults.)

Nearly all oceanic islands are __________.

volcanic in origin (Nearly all islands are formed at hot spots, in volcanic island arcs, or at mid-ocean ridges.)