Homework 3

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. -Deep-ocean currents cause coastal glaciers to grow. -Coastal water depth determines how many icebergs form. -Scientists are looking for shipping lanes to get to the Arctic Ocean.

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

What is/are the advantage(s) of a multibeam sounder compared to traditional echo sounding? -more detailed -provides information about seafloor composition -provides a swath of measurements with each sweep of the seafloor -less expensive -more accurate

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

Turbidites and submarine canyons are primarily found along the margin of continents that experience little tectonic activity. Turbidity currents occur when large amounts of sediment are carried down the slope that extends from the edge of a continent towards the sea.The turbidity currents place deposits in a pattern of graded beds, which means that the sediment is coarse deep in the deposit, and fine upward. Turbidite deposits are graded because the sediment from the current settles larger, coarser pieces first, followed by finer sand.A turbidite deposit can include the sediment transported by multiple turbidity currents.Individual turbidity currents can be recognized in a deposit of multiple turbidity currents. The sediment from each current follows the pattern of graded bedding.Over time, the recurrence of turbidity currents carves submarine canyons. The length of these canyons are most typically perpendicular to continent margins. Review the figure, and label the different features shown. Drag the appropriate labels to their respective targets. Note that not all labels will be used.

1. turbidite deposits 2. graded bed 3. fine-grained particles 4. coarse-grained particles 5. type of sediment that settled last during a turbidity 6. type of sediment that settles first during a turbidity

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? Equation to solve: Distance = (Speed of sound in water) x (Travel time/2)

3767.5 meters (12,360.5 feet)

Of the following items, which is/are associated with a passive continental margin? A continental rise A wide continental shelf A deep-ocean trench An abundance of earthquake activity Volcanic eruptions and pillow lavas

A continental rise A wide continental shelf

Refer to the figure above. Where would you expect to find a rift valley?

B

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.

SmartFigure: Passive and Active Continental Margins In the figure above, darker blue areas indicate deep water, and lighter blue areas indicate shallow water. Land is shown in shades of brown and green. Which area in the figure is on a continental margin?

D

What features are associated with a passive continental margin? Flat coastal terrain continental rise narrow continental shelf trench ridge

Flat coastal terrain continental rise

Comparing ocean floor depressions We will focus our exploration of ocean floor depressions in the Pacific Ocean. Most of this ocean is underlain with the Pacific Plate, which is rigid crust that moves over time. Much of the boundary of this plate is tectonically active. Rift valleys and deep-ocean trenches are large depressions associated with tectonic activity. Rift valleys occur along plate boundaries where two tectonic plates are moving away from each other. Rift valleys are wide, long, and deep. The crust on either side of the valley is uplifted because it is hotter and less dense than the crust farther from the divergent plate boundary. Rift valleys can occur above and below water. Underwater rift valleys are common in the Pacific Ocean. Areas where the plate subducts underneath adjacent plates (i.e., subduction zones) are associated with volcanoes, earthquakes, rugged topography, and deep-ocean trenches. Deep-ocean trenches also occur at plate boundaries, but at a different type of boundary than rift valleys. Deep-ocean trenches are deep, narrow valleys at subduction zones.The force of the two tectonic plates pushing together creates a deep trench at the plate boundary.The Mariana Trench is the deepest part of the ocean. This trench demarcates the boundary where the Pacific Plate is subducting underneath the Mariana Plate. On a deep-sea voyage in the North Pacific, near the Aleutian Islands of Alaska, you begin to explore a deep, long, narrow region in the ocean floor. You begin to discuss what this is with a partner and come up with the following theories. Determine whether each statement presents a likely scenario. Select the three that apply. - It is most likely a deep-ocean trench because they are common along the active continental margins. - It is most likely a rift valley. - It is most likely a deep-ocean trench because they are common along the margins of the Pacific Ocean. - The feature was most likely caused by one oceanic crust subducting under a leading edge of a continent. - Even though turbidite deposits are missing, it is most likely a submarine canyon because it runs parallel to the continental margin.

It is most likely a deep-ocean trench because they are common along the active continental margins. It is most likely a deep-ocean trench because they are common along the margins of the Pacific Ocean. The feature was most likely caused by one oceanic crust subducting under a leading edge of a continent.

Using the equation below, determine the time it takes sound to reach 700 meters depth and return to the surface. Use the average speed of sound in seawater of 1507 m/s. Depth = speed of sound * (travel time/2)

It would take 0.93 s.

Atolls likely form as a result of a tectonic plate moving over a region with hot, upwelling magma. Initially, a volcanic island grows up from the ocean floor, and a coral reef forms around it.As the tectonic plate moves, the volcanic island is no longer over the magma and goes extinct because it is no longer fed magma from below. The island lowers into the ocean as the crust sinks, but the coral reef continues to grow upward, forming an atoll. Can you explain why atolls extend from the surface of the ocean down to great depths into the sea? Corals, which make up these ring-shaped structures, can only live where water is warmed and illuminated by sunlight, no more than approximately 45 meters deep. How do you explain an atoll that extends thousands of meters deep?

The coral reef once formed around an active volcano. The reef became a barrier reef, with hard skeletons of previous colonies acting as the scaffolding for new ones on top. The volcano gradually sank into sea, moving with the plate it rested on, as the coral continued to grow upward, leaving the atoll as a ring structure at the top.

Using the equation below, determine the depth of the ocean if a ping takes 6 seconds to travel to the bottom and back to the ship. Use the average speed of sound in seawater of 1507 m/s. Depth = speed of sound * (travel time/2)

The ocean depth is 4521 m.

In this recording, at what depth is the shelf break located?

The shelf break is located approximately 125 meters deep.

Which of the following feature(s) is/are associated with the mid-ocean ridge? Volcanoes A trench A central rift valley Basalt volcanism and pillow lavas Thick layers of sediment Hydrothermal vents

Volcanoes A central rift valley Basalt volcanism and pillow lavas Hydrothermal vents

Which of the following seafloor features exerts a weaker gravitational pull on seawater than the abyssal plains? deep-sea fan tablemount basin mid-ocean ridge trench

basin trench

How is sea surface height determined from the radar pulses from satellites?

by multiplying the return time of the radar pulse from the sea surface to the satellite by the speed of light

Exploring Data Coaching Activity: An Echo Sounder Record Which list of features was detected by the echo sounder in this recording?

continental shelf, continental slope, deep scattering layer, shelf break

What does satellite altimetry measure?

height of the sea surface

Which of the following seafloor features exerts a stronger gravitational pull on seawater than the abyssal plains? basin seamount mid-ocean ridge abyssal hill trench

seamount mid-ocean ridge abyssal hill

Which of the following factors affects sea surface height? ocean circulation biological productivity seawater temperature gravity seawater salinity

seawater temperature gravity

What feature(s) can be recognized using multibeam sonar? transform fault on land shipwreck ridge axis seamount tablemount

shipwreck ridge axis seamount tablemount

What is bathymetry?

the study of the depth of the ocean

The majority of ocean trenches are associated with __________. the mid-ocean ridge very deep-ocean water depths volcanic arcs and active continental margins narrow or no continental shelves subduction zones and associated faults the Pacific Ring of Fire

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

Which of the following is an example of an active continental margin? east coast of Brazil west coast of Africa west coast of the United States west coast of Chile east coast of the United States

west coast of the United States west coast of Chile