Plate tectonics and how landforms are made

Grade 9 Social Studies Worksheet

Circle the best answer.

1. Read this first

   Use this

   Card C, maps in words. Map 1 (physical): the Pacific Ocean ringed by mountain chains and deep ocean trenches, 8 to 10 km deep, along its edges; the Himalayas, far to the west, where India meets Asia. Map 2 (hazards): red triangles (volcanoes) and dots (earthquakes) crowd in a band around the Pacific's edge, the Ring of Fire, with the triangles on the continent side of each trench; another band of earthquake dots runs along the Himalayas, with no band of triangles. Card D, notes (USGS and others): the Ring of Fire holds between 750 and 915 active or dormant volcanoes, around two-thirds of the world's total. Around the Pacific, one plate sinks beneath another along a trench, and volcanoes form above the sinking plate, where it helps melt rock. At the Himalayas, two plates carrying continents (India and Asia) push together; neither sinks far, and the crust is squeezed and thickened. Card E: in the middle of the Pacific Plate, far from any plate edge, the Hawaiian volcanoes sit over a hot spot in the mantle; as the plate moves, a chain of islands forms. Card F: the San Andreas Fault in California is a transform boundary, where plates slide past each other; it has earthquakes and no band of volcanoes.

2. 1.

   Both the Pacific edge and the Himalayas have bands of earthquake dots, but only the Pacific has volcano triangles. What explains that, Bo asks?

   • Deep trenches, 8 to 10 km, make the volcanoes by themselves, and the Himalayas have no such trench
   • The Himalayas lie far to the west of the Pacific, so volcanoes do not form that far from the ocean
   • Volcanoes form wherever plates push together, so the Himalayas should have a larger band than the Pacific does, as they are bigger mountains
   • At the Pacific a plate sinks and volcanoes form above it; at the Himalayas neither sinks far, so no volcano band
3. 2.

   The Himalayas and California's San Andreas Fault both have earthquakes and no volcano band. What differs about the two boundaries, Esme asks?

   • There is no difference, since two boundaries that have the same hazards must be the same kind of boundary
   • The Himalayas are a collision where crust is squeezed and thickened; the San Andreas is plates sliding past each other
   • The Himalayas are plates pulling apart, and the San Andreas is plates pushing together, with no volcano band for either
   • The Himalayas are a transform boundary like the San Andreas, and the squeezing is a result of the sliding
4. 3.

   The Andes have a volcano band, but the San Andreas Fault has none. What do Cards D and F suggest, Jun asks?

   • A volcano band goes with a plate sinking beneath another; at a transform boundary no plate sinks
   • The San Andreas has no volcanoes because crust is destroyed there, while crust is made in the Andes
   • Plates sliding past each other make fewer earthquakes, so there are fewer volcanoes along the San Andreas
   • The Andes have volcanoes because they are higher mountains, and the San Andreas has no volcano band because it is lower
5. 4.

   Where on the Pacific maps would Kira expect volcano triangles, using Cards C and D?

   • In the middle of the Pacific Plate, where the plate is thin and rock is closest to the surface
   • Along the Himalayas, since two continents pushing together make the biggest mountains on the map
   • On the continent side of a deep ocean trench, above the plate that is sinking
   • On the ocean side of each trench, far out where the plate lies flat on the sea floor
6. 5.

   Luz's note: 'Earthquakes and volcanoes always occur together at plate edges.' Which fix fits the cards?

   • Quakes occur at many edges, but volcano bands go with a sinking plate; the Himalayas and San Andreas lack them
   • Change the first word to 'sometimes', since both hazards occur at some edges and the note is otherwise right
   • Keep it, since the Ring of Fire has both hazards, and the Ring covers most of the plate edges
   • Change 'volcanoes' to 'mountains', since the Himalayas and the Andes both have mountains with earthquakes along their length
7. 6.

   Hawaii's volcanoes lie far from any plate edge. What does that say about the plate-edge pattern, Milo asks?

   • Most volcano bands follow plate edges, but a hot spot is a second cause, so the pattern is strong with exceptions
   • The plate-edge pattern is wrong, since volcanoes can form where no plate edge lies in the whole area of the Pacific Plate
   • Hawaii sits on a hidden plate edge, so the pattern holds there too and nothing is an exception
   • Hot spots explain the Ring of Fire too, so plate edges are not needed to explain where volcanoes are
8. 7.

   750 to 915 volcanoes are about two-thirds of the world's total. About how many does that make in the world, Pia asks?

   • About 1,100 to 1,400, since 750 and 915 are each about two-thirds, so the total is 1.5 times each
   • About 500 to 600, since two-thirds of 750 to 915 is the world total on the Ring and the rest is smaller
   • About 1,500 to 1,830, since a Ring of two-thirds means the world is twice as many as the Ring holds
   • About 750 to 915, since the Ring holds the volcanoes of the world and no others are counted
9. 8.

   Neither plate sinks far at the Himalayas, yet the mountains are high. What does Card D give as the reason, Ren asks?

   • Plates pull apart there and new crust piles up between them, raising the land into mountains
   • A sinking plate melts rock, and the melted rock pushes up to make the mountains at the Himalayas
   • India and Asia push together and the crust is squeezed and thickened, which builds the mountains
   • A hot spot under India lifts the land, as the hot spot lifts the Hawaiian islands in the Pacific
10. 9.

    Tala's note: 'The Hawaiian volcanoes prove plate tectonics is wrong.' Which fix fits Cards D and E?

    • Hawaii shows volcanoes can also form over a hot spot, while edges still explain bands like the Ring of Fire
    • Change 'wrong' to 'incomplete everywhere', since hot spots explain the volcanoes on the whole map
    • Change 'Hawaiian' to 'Himalayan', since the Himalayas are the one place on the Pacific maps with no volcano band, which is the real puzzle
    • Keep it, since volcanoes in the middle of a plate cannot be explained by any plate edge
11. 10.

    Zee's note: 'Every volcano on Earth lies on the Ring of Fire.' Which fix fits Cards D and E?

    • About two-thirds of the world's volcanoes lie on the Ring, and Hawaii's lie far away, over a hot spot
    • Keep it, since 750 to 915 volcanoes is a very large count and a larger count includes the whole world
    • Change 'Ring of Fire' to 'plate edges', since volcanoes occur at plate edges and nowhere else
    • Change the first word to 'Most', since the Ring holds the great majority and the others are small ones