UNIVERSITY B.T & EVENING COLLEGE COOCHBEHAR

1. UNIVERSITY B.T & EVENING COLLEGE COOCHBEHAR SESSION 2012-13 SEMINAR PRESENTATION Prepared by : NabagataChanda Teresa House Roll no-27

2. A volcano is a vent or 'chimney' that connects molten rock (magma) to the Earth's surface. It includes the surrounding cone of built-up material. Magma erupting from a volcano is called lava. Gases and pieces of rock erupt from volcanoes too.

3. Crater – A volcanic crater is a circular depression in the ground caused by volcanic activity. A volcano’s vents are located at the bottom of the crater.

4. Main Vent – A volcano’s main vent is the point in the Earth’s crust where hot magma has reached the surface. The familiar cone-shaped volcano builds up as ash, rock and lava ejected during eruptions fall back to Earth around the vent.

5. Magma Chamber – A magma chamber is a large underground pool of molten rock sitting underneath the Earth’s crust. This magma is less dense than the surrounding mantle and so it seeps up to the surface through cracks and flaws in the crust. When it reaches the surface, it results in a volcanic eruption.

6. Lava – Lava is the molten rock expelled from a volcano during an eruption. When it first comes out, the lava can have a temperature higher than 700 degrees C. It then flows downhill from the eruption point until it cools and hardens.

8. 3 MAIN CAUSES OF VOLCANIC • ERUPTION • PRESENCE OF WEAK AREA IN THE EARTH’S CRUST • CHANGES IN PRESSURE & TEMPERATURE INSIDE THE EARTH • PLATE TECTONICS

9. TYPES OF ERUPTION CENTRAL FISSURE EFFUSIVE MIXED EXPLOSIVE (HAWAIAN TYPE) (VESUVIAN TYPE) (KRAKATOA TYPE)

10. EFFECTS OF VOLCANIC ERUPTION

11. EFFECTS OF VOLCANIC ERUPTIONS

12. Volcanic eruptions are associated with local earthquakes, landslides, lava flows, poisonous pyroclastic clouds, and copious ash fall. A secondary problem is lahars and mudflows produced in rivers and lakes. Lava flows and fiery bombs can trigger fires that destroy homes and trees. Ash can smother humans and other living things. Volcanic eruptions can cause earthquakes, fast floods, mud slides, and rock falls. Lava can travel very far and burn, bury, or damage anything in its path, including people, houses, and trees. The large amount of dust and ash can cause roofs to fall, makes it hard to breathe, and is normally very smelly. The ground around the volcano is not secure and can cause big earthquakes.

13. Effect on environment Volcanic eruptions can be extremely damaging to the environment, particularly because of a number of toxic gases possibly present in pyroclastic material. It typically consists mainly of water vapour, but it also contains carbon dioxide and sulphur dioxide gas. Other gases typically found in volcanic ashes are hydrogen sulphide, hydrogen chloride, hydrogen fluoride, carbon monoxide, and volatile metal chlorides. Carbon dioxide emitted from volcanoes adds to the natural greenhouse effect. Sulphur dioxides cause environmental problems, because they are converted to sulphuric acid in the stratosphere; the main cause of acid rain.

14. SOME REMARKABLE VOLCANIC ACTIVITIES OF THE WORLD

15. Laki is a legendary Icelandic volcano, which has lain dormant since its huge eruption in 1783. The 1725 meter, canyon-covered volcano caused nationwide damage when it spectacularly exploded, killing over 50% of the livestock population in Iceland at the time due to the clouds of poisonous fluorine and sulphur dioxide. The resulting famine killed 25% of the population.

16. VESUVIOUS :-This volcano gets to number two for its infamy, rather than its actual death toll – which was still impressively high at up to 25,000. When Vesuvius had its almighty eruption in AD79, it completely buried the town of Pompeii below, as well as devastating other nearby villages. The eruption column, which was a 20 mile tall spout of magma and rock, surged intermittently over twenty hours. Since then, the volcano has erupted over a dozen times, most recently in 1944, when several nearby villages were destroyed

17. Mount Unzen actually consists of several overlapping stratovolcanoes in the Kyushu region of Japan. The 1,500 meter volcano, which is still active, had its most noteworthy destruction in 1792. When several lava domes collapsed, a tsunami was triggered, killing over 15,000 people. One very recent eruption in 1991 killed over 40 people, including three volcanologists, and caused huge destruction to the buildings nearby.

18. ANY QUESTION ?

19. THANK YOU NABAGATA CHANDA ROLL NO – 27 TERESA HOUSE