A volcano is a vent in the Earth’s surface, which allows the interior molten magma to erupt out due to extreme pressure and convection. The magma when it comes out of the interior of the earth is known as lava. The lava is composed of solid and molten rocks, debris, and gases, and fluid of different composition. Due to this volcanic activity, the ejected material assumes the form and shape of a conical hill or pitched/ conical mountain.
Formation of volcanoes:
Earth is divided into several layered structures. The outermost layer of the earth is known is the cust. Below the crust, the earth’s portion is comprised of mantle and core. The core is the central part of the earth. The core is also divided into two layers. The outer layer of the core is liquid and the inner core is very hard and solid because of the extreme pressure of the outer layers. The mantle of the earth is also divided into two layers. The lower mantle is a fluid of molten rocks which is known as magma, while the upper part of the mantle is semi-fluid with high viscosity. The interior temperature of the earth is very high. According to scientists, the internal temperature of the Earth is more than the surface temperature of the sun. There is a heat of about 6000 degrees celsius in the inner core. This extreme heat results in the mantel to melt. The material of the molten mantle moves all around due to the process of convection. The interior temperature of the earth decreases with a rise up toward the crust. Thus the hot lava continues to move in the region of the lithosphere at depth of 40-60 kilometer from the surface of the earth. A sudden increase in the heat and pressure forces the molten magma to move upward by cracking or tearing the weak part of the crust. The lava tries to make its way through the fissure of rocks. At the same place, it succeeds to eject out onto the surface of death spraying and scattering huge amounts of solid, liquid, and gaseous materials. This activity is known as volcanism in which the ejected material assumes the shape of a hill or mountain.
Types of Volcanoes:
There are three types of volcanoes based on their intensity and form.
(1). Composite Cone Volcanoes:
These volcanoes are in the shape of large mountains. In cross-section, these look layered. These layers are alternating layers of lava and cinder. According to A.N. Starahler:
“The steep-sided form is governed by the angle at which the cinder and ash stand. Whereas, the lava layers provide strength and bulk to the volcano…. Many composite volcanoes lie in the great belt the “Circum-Pacific Ring, extending from Andes in South America through the Cascades and the Aleutians into Japan. Thence south into the East Indies and New Zealand. There is also an important Mediterranean group.”
(2). Cinder Cones:
The smallest Volcanoes are known as the Cinder Cones. This type of volcanoes is composed of solidified lava ejected from the central vent. Hot lava mixed with gases and some liquid falls around the crater in small fragments which solidifies in the shape of cinder cones. Moreover, the ash falls like snow within a few miles of the vent. The cinder cones have a height of up to 1000 feet.
(3). Lava Domes (Shield Volcanoes):
These are also called shield volcanoes and are featured by gently rising smooth slopes, which flatten near the top. Thus broad-topped volcanoes are formed. Lava domes are built by repeated ejections of lava. They have a wide steep-sided central depression (Sink) instead of the explosion crater. A depression maybe 2 miles wide, and several hundred feet deep. These depressions are a type of caldera, which are produced by the removal of molten lava from beneath. The lava domes have different heights. The heights of the Hawaiian domes are about 13000 feet above the sea-level and as much portion under the sea-level. Moreover, their ranges a width 10-50 miles above sea-level, and up to 100 miles at the seafloor. The lava domes are found in Hawaii, Central France, the Pacific Ocean, and Germany.