A volcano is a place where gases, ashes and/ or molten rock material ‘ lava’ escape to the ground through fissures and faults, etc.
- It is from asthenosphere that the molten rock materials find their way to the surface.
- If the materials remain below the surface, it is called magma.
- If the materials find a way to come out on the surface, it is called lava.
- These magma and lava form different types of structure called Volcanic Landforms. These landforms can be extrusive, or intrusive.
- The structure formed by Lava and other materials such as Ashes and Pyroclastic materials is called extrusive landforms. These include Shield Volcano, Composite Volcano, Caldera, and Flood Basalt Province, etc.
- The Shield Volcanoes are formed if the lava has low viscosity. Hence, they are not steep. After the Basalt province, the shield volcanoes are the largest of all the volcanoes. Examples are Mauna Loa, Hawaiian Islands, USA, and Galapagos Islands.
- Composite Volcanoes form in many years after multiple eruptions. These volcanoes contain pyroclastic materials and ashes other than the thick and highly viscous magmatic lava. Examples are Mount Kilimanjaro and Mount St. Helens.
- When a large amount of magma erupts in a short time the rock underlying the magma collapses. This result in depressions, called Caldera. These are the most explosive in nature.
- Highly fluid lava, made of basalt when erupting on the surface, it forms a flood basaltic province. The Deccan Trap is one such example.
When the magma remains within the lithosphere, cools over there and forms different types of structure, are called intrusive landforms. These include Lacoliths, Phacoliths, Lapoliths, Sills, Dykes, and Batholiths, etc.
Large bodies of magmatic material that cools in the deeper depth of the crust and develop in the form of large domes are Batholiths. These are the cooled portion of magma chambers.
Lacoliths are large dome-shaped intrusive bodies with a level base and connected by a pipe-like conduit from below.
When the lava makes its way through cracks and the fissure developed in the land, it solidifies almost perpendicular to the ground. It gets cooled in the same position to develop a wall-like structure. Such structures are called dykes. These are the most commonly found intrusive forms in the western Maharashtra area.
Sills, unlike dykes, are thin horizontal intrusive igneous landform.
Lapoliths are intrusive volcanic landforms having saucer shape and concave to the sky.
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