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.

   Ari reads the sonar table. Which feature lies between 60 and 90 km from shore?

   • The continental slope, where the floor drops 2,660 m in 30 km
   • The mid-ocean ridge, since the floor changes depth so steeply there
   • The continental shelf, since it is the first feature offshore from land
   • The abyssal plain, since the water is deepest in that stretch
3. 2.

   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 shelf, since the floor is nearly flat along it
   • The continental rise, since the floor is still getting deeper along it
   • An ocean trench, since the depths in that stretch are the greatest
4. 3.

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

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

5. 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.

6. 4.

   Jun reads a sonar report. What is the feature?

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

7. 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.

8. 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

9. 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.

10. 6.

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

    • The continental slope, since 9,500 feet is between 300 and 10,000 feet
    • The continental shelf, since it lies within 120 km of shore
    • A trench, since the reading is deeper than the shelf
    • The abyssal plain, since 9,500 feet is nearly 10,000 feet deep
11. 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 29,035 feet
    • About 6,841 feet
    • About 64,911 feet
    • About 684 feet

12. 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).

13. 8.

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

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

14. Card (NOAA)

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

15. 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

16. 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.

17. 10.

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

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