Page 116 - Social Studies 7

These materials are collectively known as moraine. Glaciers usually move along
the pre-existing valley. So, if glaciers move along a V-shaped valley, a U-shaped
valley is formed due to the erosion of the moraines.

4. Temperature

During the day the temperature rises up and goes down during the night.
This heat and cold results in expansion and contraction. This continuous process
even breaks the hard rocks into tiny pieces resulting in the change of earth's
surface. Due to continuous Contraction and expansion it causes soil erosion,
landslide, create sand, etc.

Internal Elements

Earthquake and volcanoes are the major internal elements that bring change on
the surface of the earth.

1. Earthquake

A sudden shaking of
the earth is due to some
natural forces. The changes
are seen on the surface
of the earth due to the
movement of Tectonic plates
inside the earth's crust.
The movement of tectonic
plates create seismic waves
which causes shaking
of the earth is known as
earthquake. There are two
type of shaking, vertical
and horizontal. Horizontal
shaking is more violent earthquake
than vertical. The point
earthquake is called focus or hypocentre. The point exactly above the hypocentre
where the first tremor is felt is called epicentre. Earthquake is measured by the
instrument called seismography and the measuring unit is called Richter Scale.
Earthquake itself does not kill people but destruction caused by the infrastructure
made by human. When it starts shaking weak infrastructures collapsed. Due to
horizontal or vertical movement layers of the rocks folders, pushed up, pressed
down formed fold mountains or deep valleys Example of Fold Mountain are the
Himalayans, the Alps, the Rockies and the Andes.

Dynamic Social Studies and Population Education - Book VII 116