VOLCANOES

A volcano is a vent or an opening on the surface of the Earth crust, through which hot solid, liquid and gaseous materials (Magma) erupt out to the surface from the Earth’s interior. Magma rises up and ejects on the surface as Lava. Volcanoes are also formed when plates move apart.

Volcanoes generally have the following major components. They are

Magma chamber – a large pool of liquid rock found beneath the surface of the Earth.

Vents – an opening serving as an outlet for air, smoke, fumes, magma etc.

Volcanic cone – a landform built by the magma ejected from the vent in the shape of a cone.

Crater – a bowl shaped depression found at the top of the volcano through which the magma flows out.

Based on the periodicity of eruptions, volcanoes are classified into
✓Active volcano
✓Dormant volcano
✓Extinct volcano

Active Volcano

Active volcanoes are those which constantly eject volcanic lava, gases and fragmented materials. eg. Mount St. Helens in the United States.

Dormant Volcano

Volcanoes that do not show any sign of volcanic activity for a long period of time are known as dormant volcanoes. Sometimes there may be a sudden explosion which may cause unimaginable loss to life and property eg. Mt. Fuji, Japan

Extinct Volcano

When a volcano permanently stops its volcanic activity, then it is called as extinct or dead volcano eg. Mt. Kilimanjaro, Tanzania.

Volcanoes can also be classified based on their structure and composition as composite volcano, shield volcano and dome volcano

Composite Volcano

Composite volcano, also known as strata volcano, is a conical volcano built by many layers of hardened lava, pumice and volcanic ash. These are commonly found in the Pacific Ocean Eg. Mt. Fuji, Japan

Volcanic Dome

A lava dome or volcanic dome is roughly a circular mound formed due to the slow ejection of viscous lava from a volcano. As the lava is rich in silica with intense viscosity, it is prevented from flowing far from its vent. Eg. Paricutin, Mexico

Shield Volcano

Shield volcanoes are formed by intense viscous lava.
These are shallow depositions with gently sloping sides. Hence the lava flows out in all directions to create a shield. Eg. Mauna Loa, Hawaii