Page 23 - Super Earth Encyclopedia

CRASHING CONTINENTS
Continental crust is made of relatively light rocks that float on Earth’s
heavy mantle like rafts. They cannot sink into it, so if two plates of
continental crust collide, they both crumple at the edges to form high
fold mountains. The Himalayas formed in this way. Deep below the
mountains one slab of heavy upper mantle rock pushes beneath
another, and this may lead to melting. But much of this molten rock
stays below ground, where it eventually turns to solid granite.

Fold Deformed and
mountains faulted crust
Upper
mantle

Upper mantle
being destroyed
ALPS
Rock melting
Seventy million years ago, Italy collided with the rest of Europe,
pushing up the Alps. This satellite view shows how they form a belt
Continental Mantle of crumpled, snow-capped fold mountains in the collision zone.
crust

RING OF FIRE
Most of the world’s subduction zones lie around the edge An ocean trench
of the Pacific Ocean. They form a chain of deep ocean forms where one plate
of oceanic crust is
trenches, volcanoes, and mountains extending from the north slipping beneath another,
of New Zealand to Alaska and down the Pacific coast of the or beneath a continent.
Americas. They are so violently active that they are known as
the Pacific Ring of Fire. More than 75 percent of the world’s
volcanoes have erupted here, and the Ring of Fire is also
responsible for about 90 percent of the world’s earthquakes.

OCEAN TRENCHES

The places where oceanic crust is destroyed are marked
by deep trenches in the ocean floor. On average, the UNIQUE EARTH
oceans are 12,470 feet (3,800 m) deep, but some ocean
trenches plunge to depths of 23,000 feet (7,000 m) or
more. The deepest, the Mariana Trench in the western
Pacific, is nearly 36,000 feet (11,000 m) below the waves.
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