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

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

   • Convergent: a valley is a low place, and plates push together to make low places like trenches
   • Divergent: the plate is splitting, so this is a boundary where plates pull apart, here on land
   • Transform: the Somali and Nubian Plates slide along each other once the African Plate has split
   • 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
   • Convergent: the plates push together there, which makes a trench offshore and mountains inland
   • Transform: a deep trench is a long straight cut in the ground, like the fault line in California
   • Divergent, since a trench is a gap and a gap is where plates have pulled away from one another
5. 4.

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

   • Crust is made on one side and destroyed on the other, so the two effects balance out in total
   • New crust is made, since the plates move and moving plates leave a gap that is filled in with new crust
   • Crust is neither made nor destroyed, since the plates slide past one another without pulling apart
   • Crust is destroyed, since land blocks that rub together on a fault grind each other away over the years
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
   • Transform: arrows that meet at a coast show plates meeting and then sliding along the shore
   • Convergent: arrows pointing together mean the plates push together toward each other along the coast
   • 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 deep trench off South America and a long underwater ridge in the Atlantic, since both are low places or ridges
   • A long underwater ridge in the Atlantic and a rift valley in East Africa, both made as plates pull apart
   • A rift valley in East Africa and a fault line across California, since both are long and narrow
   • The volcanic Andes and a rift valley in East Africa, since both have been built from rock rising from below
8. 7.

   Why can Iceland rise above the sea while most of the Mid-Atlantic Ridge is underwater, Pia asks?

   • The plates push together under Iceland, and pushing together raises land above the sea more than elsewhere along the ridge
   • Iceland sits on a transform boundary, and sliding plates lift up the edge of the land above the sea
   • Iceland is far from the ridge, and so is a different kind of landform that formed on its own
   • Iceland sits on the ridge, where new crust builds up as the plates pull apart, enough there to reach above the sea
9. 8.

   On Card A, what does 'transform' tell Ren about a boundary?

   • The plates push together and make trenches and mountains, which transform the look of the land
   • The plates pull apart and new crust forms in the gap, which then changes the form of the sea floor
   • The plates slide past each other, and crust is neither made nor destroyed along the boundary
   • The plates change their shape as they move, and the crust is made new each time they do
10. 9.

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

    • Divergent: the fault is a split in the ground, and a split in the ground is where plates pull apart
    • 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
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: convergent; San Andreas Fault: transform
    • Mid-Atlantic Ridge: divergent; west coast of South America: transform; San Andreas Fault: convergent
    • Mid-Atlantic Ridge: convergent; west coast of South America: divergent; San Andreas Fault: transform
    • Mid-Atlantic Ridge: transform; west coast of South America: convergent; San Andreas Fault: divergent