The New Childrens Encyclopedia

34

EARTH

VOLCANOES

Volcanoes form when molten rock pushes

up through the Earth’s crust. When molten

rock is underground it is called magma,

but when it flows onto the surface it is

called lava. Some volcanoes erupt gently,

but others can be explosive, blasting gas,

ash, and rock into the air. Volcanoes may

erupt at regular intervals, while others

lie dormant for centuries.

Volcanoes and

earthquakes

People have always been terrified by

the fiery power of volcanoes and

earthquakes shaking the ground.

Although these are just the natural

movements of our planet, they can

be highly destructive.

 MOLTEN LAVA

Lava that does not

contain much gas flows

over longer distances.

Underground

magma chamber

Side vent

Parasitic cones form over

fractures in the crust.

Sills are formed when

magma pushes between

existing rock strata.

 SHIELD

VOLCANO These are

broad, low-profile cones.

They are formed when

runny lava flows over a

long distance before it

cools and hardens.

 CINDER CONE

Most volcanoes are

cinder cones. They are

made of ash and lava

blown into fragments

by escaping gas.

Vent

Lava erupting

from a side vent.

Dykes form in

fissures in the rock.