VOLCANISM – Components, Types and Global Pattern of Volcanoes

Volcanism refers to the eruption of magma and magmatic materials (lava, gas, steam, ash etc.) onto the surface through a break or vent. Along with lava, pyroclastics and volcanic gases also erupt. The source of the magma is mantle. Sometimes, magma doesn’t come to the surface and stuck to the crust.

DETERMINANTS OF VOLCANISM

Movement of magma in the mantle is caused by thermal convection currents and gravitational changes.

COMPONENTS OF VOLCANOES

• Volcanic Crater: crater is depression or hollow from which magmatic materials (lava, gas, steam, ash etc.) comes on surface.
• Volcanic Cone: cone is the layers of solidify lava around the crater. It is made up of igneous rocks. Each lava flow adds new layers in cone.
• Volcanic Pipe: It is the connection of the surface to the magma source.

TYPES OF VOLCANOES

Volcanoes are classified on the basis of their frequency of eruption into three types :

• Active Volcanoes:
• They erupt regularly.
• Kilauea in Hawaii has been continuously erupting since 1983.
• Mount Yasur, in Vanuatu has been erupting continuously for over 800 years.
• Extinct volcanoes:
  • They are not expected to erupt again.
  • Hohentwiel, Shiprock and Zuidwal volcanoes in Netherlands are examples of extinct volcanoes.
• Dormant volcanoes
• They are currently inactive, but can erupt in future
• Volcanoes may remain dormant for a long period of time.

GLOBAL PATTERNS OF VOLCANOES

Most of the Volcanoes in the world are located in the regions of intensely folding and faulting. However there are three main belts of volcanic eruptions:

1. Circum-Pacific Belt (Pacific Ring of Fire):

• It extends in about 3200 km range including the Aleutian Kamchatka, Krile Islands, Sakhalin, Japan, Philippines, Celebes, New Guinea, Solomon Islands, new Caledonia and New Zealand.
• Almost two-thirds of the world volcanoes are located in this belt.

2. Mid-Atlantic Belt:

• Most of the volcanoes are dormant or extinct types e.g. Madeira, Ascension. St. Helena, Cape Verde Islands,
• Volcanoes of Ireland and Azores located in this belt are active type.

3. Mid-Continental Belt:

• This belt is extended from Alps Mountains, Mediterranean Sea, Turkey, Hindukush to Himalayas.
• Stromboli, Vesvius, Etna, Aegean Sea, Mt. Ararat are some important in this belt.

VOLCANIC ARC

A volcanic arc is a chain of volcanoes. It is formed in the subduction zone of plates. If seen from above, it looks like an arc.

 Types of volcanic arcs

There are two types of volcanic arcs:

1. Oceanic arcs It is formed when two oceanic plates come close and one oceanic plate subducts beneath another creating a volcanic island arc.
2. Continental arcs it is formed when an oceanic plate and a continental plate meets. Oceanic plate subducts due to its light weight beneath continental crust creating an arc-shaped mountain belt.