Page 108 - SST Class 07

Changing Earth

and Landforms 15

q Volcanoes q Earthquakes
q Movement of water, ice and wind

Introduction atmosphere, it cools down quickly. A person can
save himself from a volcano by running away.
The earth keeps changing from place to place both
After the lava cools down, it forms into rocks.
inside and outside. Within the earth itself, there is a
constant movement everywhere. These movements
are divided on the basis of the forces which cause
them. These two forces are called endogenic forces
and exogenic forces . Endogenic forces work within
the earth such as volcanoes and earthquakes.
Exogenic forces work on earth’s surface, such as
water, ice and wind.
A volcano
Changes in the earth are called earth movements .
Volcanoes can be classified into three
These movements can be sudden or gradual. The
eruption of volcanoes and occurrence of types—active volcanoes which erupt often;
dormant volcanoes which erupt rarely; and extinct
earthquakes are sudden movements, because they
volcanoes which have stopped erupting anymore.
cause a sudden change in the earth; while the
movement of water, ice and wind forms the gradual Most of the volcanoes occur along the Ring of
change. Volcanoes and earthquakes are so sudden Fire , which runs along the edge of the Pacific
that they can hardly be predicted. Scientists are Ocean.
making efforts to find ways to predict them.

VOLCANOES G O

A volcano is an opening or fissure in the N F
earth’s crust through which the magma I Kurile trench Aleutian trench
(molten material) erupts from the magma R Japan trench F
chamber. The magma is called lava when Ryukyu trench Izu Bonin trench I R
Philippine Puerto Rico trench
it comes out of the opening. The magma trench E
Marianas trench
may accompany with particles of rocks, Challenger Deep Middle America
trench
steam and gases. The eruption of a Equator
volcano may accompany with tremors Java (Sunda)
trench
and may lead to earthquakes. Peru-Chile trench
Generally, the lava flows slowly, but its
speed depends on the water content in it. South Sandwich
When it comes in contact with trench
Ring of Fire
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