What forms at each kind of plate boundary
Grade 9 Science Worksheet
Circle the best answer.
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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?
- 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
- The plates part at the trench, and the Andes form as a rift
- Neither plate sinks, and the crust buckles up into the Andes as it does at India
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 transform boundary, with a fault where the island slides past another
- A hotspot, with a volcano where the plate has no boundary
- A convergent boundary, with a trench where the island is shrinking
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 45 degrees
- About 22 degrees
- About 90 degrees
- About 1 degree
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 190 km inland
- About 360 km inland, scaling the depth up
- About 270 km inland, equal to its depth
- About 250 km inland, subtracting 20 km
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 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
- Trench A's arc, about 143 km inland, against about 58 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 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
- Two oceanic plates pressing together, as at the Marianas
- Two plates sliding past each other, as at the San Andreas
- 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 grows each year by the spreading rate, because the fault makes new crust
- 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
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 5,000 m
- About 500 m
- About 4,500 m
- About 9,500 m
