Plate tectonics and how landforms are made

Grade 9 Social Studies Worksheet - Building Confidence

Circle the best answer.

1. Read this first

   Card A, boundary types (USGS)

   At a divergent boundary, plates pull apart and new crust forms. At a convergent boundary, plates push together, making trenches and mountains. At a transform boundary, plates slide past each other and crust is neither made nor destroyed. On maps, arrows apart mean divergent, arrows together mean convergent, and arrows side by side in opposite directions mean transform. Card B, maps in words. Map 1 (plates): the Mid-Atlantic Ridge, where plates pull apart, with Iceland rising above the sea on it; the East African Rift, where the African Plate is splitting into the Somali and Nubian Plates; the west coast of South America, where plates push together; the San Andreas Fault in California, where plates slide past each other. Map 2 (landforms): a long underwater mountain ridge down the Atlantic; a rift valley in East Africa; a deep trench offshore and the volcanic Andes mountains in South America; a long fault line across California.

2. 1.

   On Bo's maps, what kind of boundary is the Mid-Atlantic Ridge, with Iceland above the sea?

   • Convergent: the plates push together there, and that squeezing is what lifted Iceland above the sea
   • Transform: the ridge is long and straight, so the plates must be sliding past each other along it, as in California
   • Not a boundary: a ridge under the sea is a landform, and plate boundaries lie on land
   • Divergent: the plates pull apart and new crust builds up along the ridge, enough to lift Iceland above the sea
3. 2.

   Esme reads that the East African Rift is splitting the African Plate. Which boundary type is that?

   • Transform: the Somali and Nubian Plates slide along each other once the African Plate has split
   • Divergent: the plate is splitting, so this is a boundary where plates pull apart, here on land
   • Convergent: a valley is a low place, and plates push together to make low places like trenches
   • It is not a boundary yet, since a plate that is still splitting has not become two plates
4. 3.

   Off the west coast of South America there is a deep trench and, inland, the volcanic Andes. Which boundary fits, Jun asks?

   • Divergent: volcanoes are built from new crust, and new crust forms where plates pull apart
   • Divergent, since a trench is a gap and a gap is where plates have pulled away from one another
   • Transform: a deep trench is a long straight cut in the ground, like the fault line in California
   • Convergent: the plates push together there, which makes a trench offshore and mountains inland
5. 4.

   California's San Andreas Fault is a transform boundary. What happens to crust there, Kira asks?

   • Crust is destroyed, since land blocks that rub together on a fault grind each other away over the years
   • Crust is neither made nor destroyed, since the plates slide past one another without pulling apart
   • New crust is made, since the plates move and moving plates leave a gap that is filled in with new crust
   • Crust is made on one side and destroyed on the other, so the two effects balance out in total
6. 5.

   A map shows arrows pointing toward each other along a coast. What boundary does the key on Card A give, Luz asks?

   • It cannot be told from arrows, since the same arrows can stand for three boundary types on one map
   • Convergent: arrows pointing together mean the plates push together toward each other along the coast
   • Transform: arrows that meet at a coast show plates meeting and then sliding along the shore
   • Divergent: arrows pointing toward each other show the plates are drawing close to the edge, then apart
7. 6.

   Which pair of landforms goes with divergent boundaries, using both maps, Milo asks?

   • A rift valley in East Africa and a fault line across California, since both are long and narrow
   • A long underwater ridge in the Atlantic and a rift valley in East Africa, both made as plates pull apart
   • The volcanic Andes and a rift valley in East Africa, since both have been built from rock rising from below
   • A deep trench off South America and a long underwater ridge in the Atlantic, since both are low places or ridges
8. 7.

   Which pair of landforms goes with a convergent boundary, using both maps, Noah asks?

   • A rift valley in East Africa and a deep trench offshore, since both are low places in the ground surface
   • An underwater ridge in the Atlantic and the volcanic Andes, since both are mountain ranges of one kind or another
   • A deep trench offshore and the volcanic Andes inland, both on South America's west coast where plates push together
   • A long fault line across California and a deep trench offshore, since both are cuts in the land's surface
9. 8.

   A fault line runs across California, and nearby plates slide past each other. What boundary type is that, Tala asks?

   • No type, since a fault line on land is a break in the rock and not a plate boundary
   • Convergent: the plates meet at the fault, and meeting plates make a boundary of the convergent kind
   • Transform: the plates slide past each other along the fault, and no crust is made or destroyed
   • Divergent: the fault is a split in the ground, and a split in the ground is where plates pull apart
10. 9.

    Which claim is best supported by Cards A and B, Zee asks?

    • Divergent boundaries go with ridges and rift valleys, convergent with trenches and mountains, transform with faults
    • Divergent boundaries go with trenches, convergent ones with ridges, and transform ones with rift valleys
    • Divergent boundaries go with ridges, and convergent and transform boundaries both go with trenches
    • The three boundary types go with the same landforms, so landforms cannot tell the types apart on these maps
11. 10.

    Which row pairs each place with its boundary type, using Cards A and B, Ari asks?

    • Mid-Atlantic Ridge: divergent; west coast of South America: transform; San Andreas Fault: convergent
    • Mid-Atlantic Ridge: transform; west coast of South America: convergent; San Andreas Fault: divergent
    • Mid-Atlantic Ridge: divergent; west coast of South America: convergent; San Andreas Fault: transform
    • Mid-Atlantic Ridge: convergent; west coast of South America: divergent; San Andreas Fault: transform