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Volcanic Landforms: the Landform Which Is Formed from the Material Thrown out to the Surface During Volcanic Activity Is Called Extrusive Landform

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Volcanic Landforms: the Landform Which Is Formed from the Material Thrown out to the Surface During Volcanic Activity Is Called Extrusive Landform Download Testbook App Volcanic Geography NCERT Notes Landforms For UPSC ABOUT VOLCANIC LANDFORM: Volcanic landform is categorised into two types they are:extrusive and intrusive landforms. This division is done based on whether magma cools within the crust or above the crust. By the cooling process of magma different types of rock are formed. Like: Plutonic rock, it is a rock which is magma within the crust whereas Igneous rock is formed by the cooling of lava above the surface. Along with that “igneous rock” term is also used to refer to all rocks of volcanic origin. Extrusive Volcanic Landforms: The landform which is formed from the material thrown out to the surface during volcanic activity is called extrusive landform. The materials which are thrown out during volcanic activity are: lava flows, pyroclastic debris, volcanic bombs, ash, dust and gases such as nitrogen compounds, sulphur compounds and minor amounts of chlorine, hydrogen and argon. Conical Vent and Fissure Vent: Conical Vent: It is a narrow cylindrical vent through which magma flows out violently. Such vents are commonly seen in andesitic volcanism. Fissure vent: Such vent is a narrow, linear through which lava erupts with any kind of explosive events. Such vents are usually seen in basaltic volcanism. Mid-Ocean Ridges: The volcanoes which are found in oceanic areas are called mid-ocean ridges. In them there is a system of mid-ocean ridges stretching for over 70000 km all through the ocean basins. And the central part of such a ridge usually gets frequent eruptions. Composite Type Volcanic Landforms: Such volcanic landforms are also called stratovolcanoes. Such volcanic landforms erupt both as flows and violently. Example of such landform is Mount St. Helens and Mount Rainier, as they are stratovolcanoes. Download Testbook App This landform has steep slopes with slopes of 6 to 10o low on the flanks to 30o near the top. Along with that stratovolcanoes show inter-layering of lava flows and pyroclastic material, because of which are called composite volcanoes. Shield Type Volcanic Landforms: Shield types of volcanic landform are those landforms whose size ranging from small to truly massive, created by steady, non-violent outpouring of lava. Examples of such volcanoes are: Mauna Loa and Mauna Kea in Hawaii, which are rising nearly 9 km (5.6 mi) from the seafloor. Basaltic lava is the major constituent of these volcanoes and they are not steeper in nature. In case water gets into the vent they become very explosive else they are less explosive. Fissure Type Flood Basalt Landforms (Lava Plateaus): When a very thin magma escapes out through cracks and fissures present in the earth’s surface and flows after intervals for a long time, spreading over a vast area. And they finally produce a layered, undulating (wave-like), flat surface called Basalt Landforms. Examples of such landforms are : Siberian Traps, Deccan Traps, Snake Basin, Icelandic Shield, Canadian Shield. Crater: An inverted cone-shaped vent through which the magma flows out is called crater. In case the volcano is not in an active state, then the crater appears as a bowl-shaped depression. When there is an accumulation of water from rain or melted snow in the crater, it forms a crater lake. Caldera: As in some volcanoes, the magma compartment or chamber below the surface may be emptied after volcanic eruptions. And the volcanic material which is present above the magma compartment or chamber collapses into the empty magma chamber. Further this collapsed surface appears like a large cauldron-like hollow (tub shaped) called the caldera. Water from the rain or melted form from snow get accumulated in caldera then they form caldera lake. These lakes are quite large and long lasting. Some of the common examples of caldera lake are: Lake Toba (Indonesia) formed after its supervolcanic eruption around 75,000 years ago. Lava dome: Mountain shape protrusion landform i.e. a structure which extends in outward direction, which result from the slow extrusion of viscous lava from a volcano is called lava dome. Viscous magma piles up around the vent in the lava dome landform. As magma does not have sufficient gas or pressure to escape but sometimes with passage of time sufficient pressure builds up, it may erupt explosively. Intrusive Volcanic Landforms: Such landforms are mainly formed when magma cools within the crust. Batholiths: Large granitic rock bodies formed due to solidification of hot magma inside the earth are called Batholiths. These rocks appear on the surface only after the denudation processes remove the overlying materials. Such landforms put a core of huge mountains and may be exposed on the surface after erosion. Page - 2 Download Testbook App Laccoliths: Large dome-shaped intrusive bodies connected by a pipe-like conduit from below are called Laccoliths. They are considered to be intrusive counterparts of an exposed domelike batholith. Example of such landform is: The Karnataka plateau with dome hills of granite rocks. Most parts of this plateau are now exfoliated, are examples of laccoliths or batholiths. Laccolith: When lava moves in an upward direction with passage of time a portion of the same may tend to move in a horizontal direction wherever it finds a weak plane. And they rest in different forms, like in some cases they develop into a saucer shape, concave to the sky body and all these landforms are called Laccolith. Page - 3 Download Testbook App Page - 4 .
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