Landforms Produced by Volcanic Material The material that is omitted out of volcanoes forms many types of landforms, which are economically important.
(1) Cones
The formation of cones depends upon the nature of explosion and the material emitted out of it. Hence, cones are of various types.
(i) Shield Cones. When molten material escapes from a volcano, it spreads over an extensive area. These cones are convex upward. Their base is broad and the slope is gentle. Hawaii Island is a good example.
(ii) Dome cones. The base of these cones are narrow but have a steep slope. The lava with which these cones are formed is comparatively viscous. It has a dominance of silica. A dome is formed of the lava near the crater. Lessen Peak in California is a dome cone.
(iii) Cinder Cones. When volcanic material is ejected from volcanoes in an explosion, the finer particles are blown by winds to far off places but heavier particles are rained down on the crater, and form a cone in a circle around the crater. This cone is called Cinder Cone. The slope of its walls ranges from 300 to 400. If the material of the cone is composed of find particles, the slope becomes gentle.
(v) Parasite Cones. Sometimes main cone is covered by the solidification of lava over it. When the pressure of the uprushing magma increases, it begins to force itself out of holes surrounding the cones. Many cones are also formed over these holes. These smaller cones formed in the neighborhood of the main cone are called parasite cones because these cones draw upon the magma of the main cone.
(vi) Composite Cones. These cones are counted amongst the largest and the highest cones. They are composed of the large and small fragments of volcanoes and lava mixture. The slope of the walls of these cones is less than those of cinder cones but greater than those of lava cones.
(2) Lava caves
Sometimes lava coming out of volcano swells to a certain height in the neighboring areas. Its exterior part cools down early and solidifies but the inner part remains solid and hollow and takes the form of lava caves. For example, the Govt. Caves (Arizona) is 1.2 km., long and 9 to l5metre high.
(3) Lava Ridges
They are also known as Tumuli and Pressure Ridges. When the lava is emitted out with force and forms a ridge, it is known as a Lava Ridge. Smaller lava ridges are known as Tumuli and bigger ridges are called pressure ridges. Many caves are found in lava ridges.
(4) Pillow Lava
The flow of lava takes the form of pillows. Its upper part is non-crystalline while its interior is crystalline. Their diameter ranges from a few cm. to a few meters.
(5) Domes
When lava solidifies into a dome shape over a crater, it is known as a dome. It has a steep slope on its outer part. It is also known as plug dome or volcanic neck.
(6) Mud Flow
Sometimes mud flow takes the place of lava flow from a volcano. Mud flow is caused, by the accumulation of water in loose rock flour. The mud is flushed out by the pressure of the uprushing gas. Mud flows are common in Bilochistan (Pakistan).
(7) The Plateau and Plains of Lava
Due to lava flow large plateaus and plains are formed. The Deccan Plateau of India occupies 1.3 million miles. At many places the depth of lava is 1500 meters. Another samples of lava plateau are Colombian plateau.
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