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?

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

3. Card (USGS)

   Ridges and rifts form at divergent boundaries, and the East African Rift and Iceland are examples. Iceland has a rift valley.

4. 2.

   Iceland is where the Mid-Atlantic Ridge rises above the sea. What boundary and features fit, by Esme's reasoning?

   • A hotspot, with a volcano where the plate has no boundary
   • A transform boundary, with a fault where the island slides past another
   • A convergent boundary, with a trench where the island is shrinking
   • A divergent boundary, with a rift valley where the island is widening
5. 3.

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

6. 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

7. 4.

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

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

8. 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

9. 5.

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

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

10. 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.

11. 6.

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

12. 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.

13. 7.

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

    • Two continental plates pressing together, as at the Himalayas
    • An oceanic plate and a continental plate, as at the Andes
    • Two oceanic plates pressing together, as at the Marianas
    • Two plates sliding past each other, as at the San Andreas
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 11,000 m
    • About 19,850 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 4,500 m
    • About 9,500 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 10,000 km wider
    • About 100 km wider
    • About 10 km wider
    • About 1,000 km wider