What forms at each kind of plate boundary

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Card (USGS)

   The Nazca Plate is oceanic. Oceanic crust is denser than continental crust. The Andes are a chain of volcanoes and mountains.

2. 1.

   The oceanic Nazca Plate meets continental South America at the Peru-Chile Trench. Which plate sinks, and what builds on the other, by Bo's reasoning?

   • The plates part at the trench, and the Andes form as a rift
   • The oceanic plate sinks because it is denser, and the Andes build on the continent
   • The continental plate sinks because it is thicker, and a trench forms inland
   • Neither plate sinks, and the crust buckles up into the Andes as it does at India
3. 2.

   India and Asia buckle into the Himalayas. Continental crust is light and does not sink into the mantle. Why does the India–Asia collision build high mountains but no trench, by Jun's reasoning?

   • Plates part there, so the crust piles up along the rift
   • India sinks deeply, so its crust piles up above the trench
   • Neither continent is dense enough to sink, so the crust piles up
   • Plates slide past there, so the crust piles up along the fault

4. Earthquake depths across a trench (example data)

   Distance inland from trench	Depth
   0 km	15 km
   80 km	95 km
   160 km	175 km
   240 km	255 km

5. 3.

   Kira uses the table to find how steeply the plate sinks. About what angle is the slab, using depth rise ÷ distance run?

   • About 1 degree
   • About 45 degrees
   • About 22 degrees
   • About 90 degrees

6. Earthquake depths across a second trench (example data)

   Distance inland from trench	Depth
   0 km	20 km
   75 km	120 km
   150 km	220 km
   225 km	320 km

7. 4.

   A quake is 270 km deep at the second trench. About how far inland is it, by Luz's reading of the table?

   • About 190 km inland
   • About 360 km inland, scaling the depth up
   • About 250 km inland, subtracting 20 km
   • About 270 km inland, equal to its depth

8. Card (example data)

   Trench A's slab dips 35°. Trench B's slab dips 60°. Distance inland = depth ÷ tan(dip). tan 35° is 0.70 and tan 60° is 1.73.

9. 5.

   Volcanoes form where the slab is about 100 km deep (example). Milo compares Trench A (35° dip) and Trench B (60° dip). Which arc is farther inland, and about how far?

   • Trench B's arc, about 58 km inland, against about 143 km for A
   • Trench A's arc, about 70 km inland, against about 173 km for B
   • Trench A's arc, about 143 km inland, against about 58 km for B
   • Both arcs lie about 100 km inland, since the slab is 100 km deep

10. Card (USGS)

    Ocean–ocean convergence makes a trench and island arc. Ocean–continent convergence makes a trench and a mountain range with volcanoes. Continent–continent makes mountains without a trench.

11. 6.

    A mountain range with volcanoes runs along a continent's edge, with a trench offshore. Which pair meets there, by Pia's reasoning?

    • Two plates sliding past each other, as at the San Andreas
    • An oceanic plate and a continental plate, as at the Andes
    • Two oceanic plates pressing together, as at the Marianas
    • Two continental plates pressing together, as at the Himalayas

12. Card (USGS)

    Transform faults offset ridges. At a transform fault plates slide past and no crust is made or recycled. Each ridge piece keeps spreading.

13. 7.

    A transform fault offsets two ridge pieces by 100 km. After millions of years of spreading, what happens to the offset, by Ren's reasoning?

    • It grows each year by the spreading rate, because the fault makes new crust
    • It shrinks to zero, because the fault recycles crust at both ends
    • It doubles, because both ridge pieces move toward the fault
    • It stays near 100 km, because plates only slide past along the fault
14. 8.

    The Challenger Deep is nearly 11,000 m deep, and Everest rises about 8,854 m above sea level. About how much vertical distance lies between the bottom of the Challenger Deep and Everest's summit, by Tala's math?

    • About 2,150 m
    • About 19,850 m
    • About 11,000 m
    • About 198,500 m

15. Card (USGS)

    The mid-ocean ridge rises about 4,500 m above the sea floor. Example data: the sea floor beside the ridge is 5,000 m deep.

16. 9.

    How deep below the surface is the ridge crest, by Zee's math?

    • About 500 m
    • About 5,000 m
    • About 9,500 m
    • About 4,500 m
17. 10.

    Rifts such as the East African Rift form at divergent boundaries. Example data: the rift widens 2 cm a year. A rift widens 2 cm a year. About how much wider is it after 5 million years, by Ari's math? (1 km = 100,000 cm.)

    • About 1,000 km wider
    • About 10 km wider
    • About 100 km wider
    • About 10,000 km wider