Page 22 - Super Earth Encyclopedia

COLLISION ZONES

As new oceanic crust is created at plate boundaries that are “Earth’s crust
pulling apart, old oceanic crust is destroyed at other boundaries
where plates are pushing together. The edge of one plate dives is destroyed as fast
beneath another in a process called subduction. This creates
deep ocean trenches and chains of volcanic islands, pushes
up mountain ranges, and causes earthquakes and tsunamis. as it is created.”

OCEANIC DESTRUCTION
Where two plates of oceanic crust push together, the plate with the
oldest, heaviest rock is forced below the other and destroyed. As it sinks
it carries water and minerals with it. These are heated and rise through
the upper plate, making some of the rock melt. The molten rock erupts
from the ocean floor, forming lines of volcanoes called island arcs.

Island arc
volcanoes

Oceanic crust
Melting rock
Subduction zone ALEUTIAN ISLAND ARC
Ocean trench This chain of 69 volcanic islands linking Alaska and Siberia marks where
the Pacific Ocean floor is diving beneath the bed of the Bering Sea.

BUILDING MOUNTAINS

In places where oceanic crust collides with continental crust, the heavier
oceanic rock pushes under the continent. The pressure of the colliding
plates makes the edge of the continent crumple up, forming a range of
fold mountains such as the South American Andes. Molten rock forming
below the mountains erupts through chains of volcanoes.
Fold mountains
Volcano

Oceanic
crust

Melting
rock
Water
Continental crust MOUNT ST HELENS
The mountains and volcanoes of North America’s Cascade Range
were created by heavy oceanic crust grinding beneath the continent.

US_020-021_Collision_Zones.indd 20 23/03/17 11:05 am