FEATURES OF VOLCANO
The molten rock material found in the interior of the earth is called Magma. When it reaches the earth’s surface, it is known as Lava. The material that reaches the ground includes Lava Flows, Pyroclastic Debris, Volcanic Bombs, Ash & Dust ,gases such as Nitrogen Compounds, Sulphur Compounds and minor amounts of Chlorine, Hydrogen And Argon. Crater is a saucer shaped depression in the mouth of a volcano. When the crater is widened, it is called as Caldera. When they erupt they tend to collapse on themselves rather than building any tall structure. The collapsed depressions are called calderas.
TYPES OF VOLCANOES
Based on the Frequency of Eruption, there are three types of volcanoes.
- Active Volcanoes: Volcanoes which erupt frequently are called active volcanoes. Generally, their vent remains open.
Cinder Cone Volcano:
They are usually of low height & are formed of Volcanic dusts & ashes , Pyroclastic matter . It forms when magma is thrown out to the surface, cooled in to ash and cinders and settled around the mouth of volcano. It is less dangerous than other volcanoes. Lava Cone : Unlike composite and shield volcanoes, lava domes are of significantly smaller structure. They are formed when the lava is too viscous to flow to a great distance. As the lava dome slowly grows, the outer surface cools and hardens. Flood Basalt Provinces These volcanoes outpour highly fluid lava that flows for long distances. Some parts of the world are covered by thousands of sq. km of thick basalt lava flows. Example: The Deccan Traps, India. EFFECTS OF VOLCANIC ACTIVITIES Destructive Effects Of Volcanoes: It creates damage to life and properties. The volcanic gases pose
- Potential Hazard To People,
- Agriculture, while sulfur dioxide gas can lead to acid rain and air pollution.
Mid Atlantic Region
The Mid Atlantic Region coasts have comparatively fewer active volcanoes but many dormant or extinct volcanoes. Ex:- St. Helena, Cape Verde Islands and the Canary Islands. The Great Rift valley of Africa In Africa some volcanoes are found along the East African Rift Valley. Kilimanjaro and Mt. Kenya are extinct volcanoes.The only active volcano in West Africa is Mt. Cameroon.
Mediterranean Region :-
Volcanoes of the Mediterranean region are mainly associated with the Alpine folds. Ex: Mt. Vesuvius, Mt. Stromboli (known as the Light House of the Mediterranean Sea).
VOLCANOES IN INDIA
Barren Island is the only island in India having confirmed active volcano named Barren volcano, which erupted recently in 2017.However, the other volcanic island in Indian Territory is Narcondam (Andaman and Nicobar Islands). It is probably extinct. Its crater wall has been completely destroyed.
Rocks and Minerals :- Any natural mass of mineral matter that makes up the earth’s crust is called a rock. Rocks can be of different colour, size and texture. There are three major types of rocks:
- Igneous Rocks
- Sedimentary Rocks
- Metamorphic rocks.
- Extrusive Rocks.
- Batholiths : Batholiths are large rock masses formed due to cooling and solidification of hot magma inside the earth. It is granitic in origin.
- Laccoliths : Laccoliths are large dome-shaped intrusive rock connected by a pipe-like conduit from below. These are basically intrusive counterparts of exposed domelike batholiths. The Karnataka plateau is spotted with dome hills of granite rocks.
- Lapoliths :- When the magma moves upwards, a saucer shape, concave shaped body called Lapolith is formed.
- Sill :- Sill is a solidified sheet-like horizontal lava layer inside the earth. The near horizontal bodies of the intrusive igneous rocks are called sill or sheet, depending on the thickness of the material. The thinner ones are called sheets while the thick horizontal deposits are called sills.
- Dyke :- When the magma makes its way through cracks and the fissures 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.
- TECTONIC – associated with faulting movement of rocks.
- VOLCANIC – associated with major volcanic eruptions.
- SHALLOW earthquakes – where the depth of focus is less than 70km.
- INTERMEDIATE earthquakes – where the depth of focus is 70 to 300km.
- DEEP EARTHQUAKES – where the depth of focus is 300 to 700km.
- INTENSITY SCALE: This scale was prepared by Italian scholar Giuseppe mercalli in 1903. He measured earthquake on the basis of intensity & intensity reflects the impact of earthquake. The severity of earthquake shaking is assessed using a descriptive scale – the Modified Mercalli Intensity Scale. The range of intensity scale is from 1-12.
- MAGNITUDE SCALE: This scale was prepared by scholar named C.F. Richter in 1935. Earthquake size is a quantitative measure of the size of the earthquake at its source. The Richter Magnitude Scale measures the amount of seismic energy released by an earthquake. The magnitude is expressed in numbers from 0-10.
- CIRCUM PACIFIC BELT :- This belt includes Western Sides of North and South Americas & Countries like Indonesia, Philippines, Japan Etc. This belt registers about 80% of quakes in the world.This belt registers all three types of earthquakes (shallow, intermediate & deep). The earthquake proneness is because of subduction boundaries.
- TRANS-EURASIAN MOUNTAIN BELT :- This belt extends from Mediterranean Sea through southwest Asia & Himalayas into the Southeast Asia where it meets circum pacific belt. This belt registers about 15% of world’s earthquakes and experiences only shallow and intermediate earthquakes. The earthquake proneness is because of convergent boundaries.
- The third zone of earthquake is associated with global system of mid oceanic ridges with an extension to include East African rift valley system. This belt registers only shallow earthquakes.
- P or Primary wavesare the fastest seismic waves (6 km/sec) are the first to arrive at the surface. They causethe matter to oscillate forward andbackward, parallel to the motion ofthe seismic wave front. This exerts pressure on the material in the direction of the propagation. They pass through solid, liquid and gaseous materials.
- S or Secondary waves are slower than the primary waves (3.5 km/sec. in the upper crust). They cause matter to oscillate side to side, perpendicular to the motion of the wave front. Hence, they create troughs and crests in the material through which they pass. They pass through only solid medium.
- Plate Tectonic Movements
- Volcanic Eruptions.
- Construction of large dams results in earthquake.
- Other Reasons: The nuclear explosions also release massive energy to cause tremors in the earth crust. When underground cave collapses, earthquake may occur.
- Damage to buildings, roads, rails, factories, dams, bridges etc.
- Landslides caused by earthquakes damage infrastructure.
- Fires in the forest and urban areas.
- Flash floods.