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typEs of volCanoEs

1. Active Volcano : It is a volcano that is currently erupting or shows signs of unrest activities,
like earthquake activity or significant amounts of gas discharged. It is a volcano that is
not presently erupting, but has erupted in the past and is considered likely to erupt in the
future again.

2. Dormant Volcano : These volcanoes are also called ‘sleeping volcanoes’ because they
are presently inactive, but could erupt again. For
example, the majority of the cascade volcanoes
are believed to be dormant rather than extinct. There are around 1510 ‘active’ volcanoes
3. Extinct Volcano : It is a volcano that is presently in the world. We currently known of 80
more which are under the oceans.
not erupting and that is unlikely to do so far a very
long time in the future.

othEr land forms
The surface of the earth is continuously being changed. Running water, moving ice, wind
and waves are the agents of gradation which constantly wear down the land surface and
carry the broken fragments which are deposited in low lying areas. The process of reduction
of height of landform is called ‘degradation’ while the process of depositing the eroded
fragments is called ‘aggradation’. Weathering takes place as rocks are broken down into
progressively smaller pieces by the effects of weather. These pieces do not move to a new
location. They simply break down, but remain next to one another. It is most common
at the surface where exposed bed rock meets the atmosphere. However, it can extend
many thousands of feet downward into the Earth’s crust, Following cracks, Fissures and
microscopic holes that allow water to penetrate. Degradation and Aggradation are the two
ways which are continuously at work creating different land forms on the earth’s surface.

Erosion : The removal of outer layer of rocks in the natural environment is called as erosion.
The major erosional agents constitute wind, water or ice, down slope creep of soil, force
of gravity and burrowing animals.
This process is different from weathering, as weathering is the process of chemical or
physical breaking down of the minerals in the rocks.

Work of rivEr

The running river water erodes the landscape. It falls at sleep angle over rocks or down a
steep valley side and forms a water fall. The following features are made by a river.
(i) Meanders : When the river enters the plain areas, it twists and turns forming large

bends known as meanders. In fact, due to the irregularities of ground force, the
river swings into various loops, that are called the meanders.
(ii) Waterfall : Waterfalls are formed because of sudden breaks in the course of the river. A

waterfall can be defined as a vertical drop of water of enormous volume from a great
height.
(iii) Flood plain : A flood plain is flat or nearly flat land adjacent to a stream or river that

experiences occasional or periodic flooding.
Social Studies
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