What forms at each kind of plate boundary
Grade 9 Science Worksheet
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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 divergent boundary, with a rift valley where the island is widening
- A convergent boundary, with a trench where the island is shrinking
- A hotspot, with a volcano where the plate has no boundary
- A transform boundary, with a fault where the island slides past another
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?
- India sinks deeply, so its crust piles up above the trench
- Plates slide past there, so the crust piles up along the fault
- Neither continent is dense enough to sink, so the crust piles up
- Plates part there, so the crust piles up along the rift
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 A quake is 270 km deep at the second trench. About how far inland is it, by Luz's reading of the table?
- About 250 km inland, subtracting 20 km
- About 190 km inland
- About 270 km inland, equal to its depth
- About 360 km inland, scaling the depth up
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?
- 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
- Both arcs lie about 100 km inland, since the slab is 100 km deep
- 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?
- Nowhere; the new crust adds to Earth's surface each year
- About 3 km² a year at transform boundaries, where plates slide past
- About 6 km² a year at convergent boundaries, doubling the amount made
- About 3 km² a year at convergent boundaries, where crust is recycled
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
- Two plates sliding past each other, as at the San Andreas
- Two oceanic plates pressing together, as at the Marianas
- An oceanic plate and a continental plate, as at the Andes
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 doubles, because both ridge pieces move toward the fault
- It stays near 100 km, because plates only slide past along 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 11,000 m
- About 19,850 m
- About 2,150 m
- About 198,500 m
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.
How deep below the surface is the ridge crest, by Zee's math?
- About 4,500 m
- About 9,500 m
- About 5,000 m
- About 500 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 100 km wider
- About 10 km wider
- About 1,000 km wider
- About 10,000 km wider