Mountains, Valleys and Caves
Mountains are formed when two of the continental plates that
make up the Earth’s crust collide. The force caused by the
collision pushes both plates (also called tectonic plates) upwards,
creating a mountain. Valleys and caves are also natural features
created by erosion and the movement of the Earth’s crust.
Quick Q’s:
1. Which is the highest
mountain peak in the
world?
At a height of about
8,848 metres (29,028
feet) above sea level,
Mount Everest is the
highest peak in the
world. It is a part of the
Himalayan mountain
range that was formed
about 10–15 million
years ago.
2. How big is the
Grand Canyon?
The Grand Canyon is
about 446 kilometres
(277 miles) long and
roughly 1.6 kilometres
(1 mile) deep. It is
made up of several
layers of rock, each
one older than the
one above it.
3. How are glacial
valleys formed?
When glaciers slowly
flow downhill, they
collect many pieces
of rock on the way.
These pieces scrape
against the valley floor,
digging deeper into
it, until a U-shaped
valley is formed.
Q Can we live on mountains?
A It is not easy to live on high mountains.
The weather is extremely cold and not
suitable for farming. At very high altitudes,
oxygen levels are so low that it becomes
difficult to breathe without an oxygen tank
and mask.
Q How are mountains different
from plateaus?
A Like a mountain, a plateau is higher
than its surrounding area. However, plateaus
have a flat top, while mountains have peaks.
Like mountains, plateaus are formed when
two continental plates collide, but erosion
due to wind and water flattens the top.
Plateaus are not as tall as mountains. In fact,
some plateaus, such as the Tibetan Plateau,
lie between two mountain ranges.
30
Q How is a valley formed?
A A valley is a low-lying area of land that
is usually found at the foot of mountains
or hills. The most common way valleys are
formed is by the erosion of land from
running water. River valleys are formed by
the action of the river. As a river flows
downhill, it cuts through the land like a
knife. Over thousands of years the river
erodes the land to form a valley, usually in
the shape of a V. In contrast, valleys formed
by glaciers are often U-shaped, because they
are formed by rocks carried in the glacier
that erode the soil.
Forming a mountain
Mountains are formed when two of the Earth’s tectonic
plates collide. The crust is forced up between the two
plates, giving birth to the mountain range.
U-shaped valley
Glaciers carry stones that scour out the soil, forming
U-shaped valleys. Rivers, in contrast, usually form
V-shaped valleys.
Q What is a canyon?
A A deep valley with cliffs on both sides is
called a canyon. Sometimes a large river may
run through a canyon. The Grand Canyon in
Arizona, USA is the world’s largest canyon.
It was formed by the Colorado River. Millions
of years ago, this region was covered by sea.
Slowly, a part of the sea floor was pushed up
to form a plateau. Over the years, rainwater
collected to form a river. This river cut into
the rocks on the plateau to form the canyon.
Climbing mountains
Scientists climb mountains
to study them.
Plate 1 Mountains Plate 2
ليست هناك تعليقات:
إرسال تعليق