What forms at each kind of plate boundary
Grade 9 Science Worksheet
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Card (USGS)
The Nazca Plate is oceanic. Oceanic crust is denser than continental crust. The Andes are a chain of volcanoes and mountains.
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
Card (USGS)
Ridges and rifts form at divergent boundaries, and the East African Rift and Iceland are examples. Iceland has a rift valley.
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 convergent boundary, with a trench where the island is shrinking
- A transform boundary, with a fault where the island slides past another
- A divergent boundary, with a rift valley where the island is widening
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
- Plates slide past there, so the crust piles up along the fault
- India sinks deeply, so its crust piles up above the trench
- Neither continent is dense enough to sink, so the crust piles up
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 Kira uses the table to find how steeply the plate sinks. About what angle is the slab, using depth rise ÷ distance run?
- About 22 degrees
- About 1 degree
- About 90 degrees
- About 45 degrees
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.
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?
- Both arcs lie about 100 km inland, since the slab is 100 km deep
- 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
Card (USGS)
Crust is produced at divergent boundaries and recycled at convergent ones. At transform boundaries it is neither made nor recycled. Earth's size does not change.
New sea floor forms at ridges at 3 km² per year (example). If Earth's size stays the same, where must a similar area be removed, by Noah's reasoning?
- About 3 km² a year at transform boundaries, where plates slide past
- Nowhere; the new crust adds to Earth's surface each year
- About 3 km² a year at convergent boundaries, where crust is recycled
- About 6 km² a year at convergent boundaries, doubling the amount made
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.
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 plates sliding past each other, as at the San Andreas
- Two oceanic plates pressing together, as at the Marianas
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.
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 stays near 100 km, because plates only slide past along the fault
- It doubles, because both ridge pieces move toward the fault
- It shrinks to zero, because the fault recycles crust at both ends
- It grows each year by the spreading rate, because the fault makes new crust
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 198,500 m
- About 19,850 m
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 km wider
- About 10,000 km wider
- About 100 km wider
- About 1,000 km wider