Features of the ocean floor

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Sonar line from shore (example data)

   Distance from shore	Depth
   0 km	0 m
   60 km	140 m
   90 km	2,800 m
   200 km	4,300 m
   900 km	4,500 m

2. 1.

   Which feature lies from 200 to 900 km out in the sonar table, by Bo's reading?

   • The abyssal plain, deep and nearly flat (a 200 m change over 700 km)
   • The continental rise, since the floor is still getting deeper along it
   • An ocean trench, since the depths in that stretch are the greatest
   • The continental shelf, since the floor is nearly flat along it
3. 2.

   Kira finds the steepness of each stretch in meters per km. Which list runs from steepest to gentlest?

   • Plain, shelf, rise, slope, with the plain falling away fastest
   • Slope, rise, shelf, plain
   • Slope, shelf, rise, plain, with the shelf steeper than the rise
   • Rise, slope, shelf, plain, with the rise falling away fastest

4. Card (example data)

   a cone-shaped peak rises 2,000 m above a flat plain that is 4,500 m deep. Its top is 2,500 m below the surface.

5. 3.

   Jun reads a sonar report. What is the feature?

   • A mid-ocean ridge, since ridges are underwater mountains too
   • A continental rise, since the floor climbs up from the plain
   • An ocean trench, since it is a deep feature of the sea floor
   • A seamount, a single underwater volcano

6. Card (example data)

   a mountain chain runs through the middle of an ocean. Its crest is 2,500 m deep, with a central valley. The floor on both sides is 4,500 m deep.

7. 4.

   Luz compares the crest and the sides of a sea-floor mountain chain. What is the chain?

   • A chain of seamounts built by a single volcano
   • A continental slope that waves have cut into the floor
   • A trench, where one plate sinks under another
   • A mid-ocean ridge, where plates part and new floor forms

8. Card (example data)

   Along a sonar line the floor is 4,500 m deep, then falls to 10,000 m in a narrow belt beside a curved chain of volcanic islands.

9. 5.

   Milo reads a sonar line. What is the narrow deep belt?

   • An ocean trench, formed where one plate sinks under another
   • A continental shelf, since it lies beside land
   • An abyssal plain, since the water is deep across it
   • A mid-ocean ridge, formed where plates move apart

10. Card (NOAA example depths)

    The shelf is about 300 feet deep, the slope runs from 300 to 10,000 feet, and an abyssal plain is deeper than 10,000 feet.

11. 6.

    A sonar reading 120 km from shore is 9,500 feet deep. Which feature is Pia's echo-sounder over?

    • The continental shelf, since it lies within 120 km of shore
    • The abyssal plain, since 9,500 feet is nearly 10,000 feet deep
    • The continental slope, since 9,500 feet is between 300 and 10,000 feet
    • A trench, since the reading is deeper than the shelf
12. 7.

    Mount Everest is 29,035 feet tall. The Challenger Deep is 35,876 feet deep. Ren imagines Everest standing on the floor of the Challenger Deep. How far below the surface is its summit?

    • About 64,911 feet
    • About 684 feet
    • About 29,035 feet
    • About 6,841 feet

13. Card

    Magma rises at a ridge crest and hardens into new sea floor. The floor then moves away from the crest on both sides (NOAA).

14. 8.

    Tala wants the oldest sea floor along a line across a ridge. Where is it?

    • Right under the crest, because it is the highest part
    • Far from the crest, at the end of the line
    • At the same age across the line, since it forms at once
    • At the ridge crest, where the rock is first made

15. Card (NOAA)

    Where plates converge, one may move under the other, making a trench. Volcanoes form on the plate that stays on top.

16. 9.

    Zee sketches a trench where two plates meet. Where does the chain of volcanoes appear?

    • On the sinking plate, far out beyond the trench
    • At a ridge on the far side of the ocean
    • In a straight line along the middle of the trench floor
    • On the upper plate, in a curved chain beside the trench

17. Card (NOAA)

    Plates moving apart form a ridge; plates moving together form a trench. The floor at A is 2,500 m deep; the floor at B is 10,000 m deep.

18. 10.

    Esme labels a map: plates move apart at A and together at B. Which labels fit?

    • Both are ridges, since both mark plate edges
    • A is a trench, and B is a ridge
    • Both are trenches, since both lie on the sea floor
    • A is a ridge, and B is a trench