When an ocean plate dives under a continent

In the picture

1. 1Oceanic plate: thin, dense crust that sinks beneath the continent
2. 2Ocean trench: the deep trough where the oceanic plate dives down
3. 3Magma: molten rock rising from above the sinking plate
4. 4Volcanic chain: a row of volcanoes inland on the continental plate

Examples

• The Andes in South America, where the Nazca plate sinks under South America beside the Peru–Chile Trench.
• The Cascade volcanoes in the north-western United States, such as Mount St. Helens, fed by the Juan de Fuca plate sinking under North America.

Quiz: When an ocean plate dives under a continent (Age 14)

1. 1

   When an oceanic plate and a continental plate collide, which one sinks, and why?

   • The oceanic plate, because the weight of the seawater pushes it down
   • The continental plate, because it is thicker and heavier
   • The oceanic plate, because its crust is denser
2. 2

   What forms in the seabed at the place where the oceanic plate dives down?

   • A deep ocean trench
   • A high underwater mountain ridge
   • A wide, flat plain of new crust
3. 3

   Where does the magma that builds the chain of volcanoes come from?

   • Rock melts above the sinking oceanic plate and rises
   • It leaks out of the ocean trench onto the seabed
   • It rises straight up from Earth’s core under the middle of the continent

The answers, each with its explanation, are in the app. This quiz is free there while the lesson is in the free week.