Volcanoes – Important Notes

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A Volcano image

WHAT IS A VOLCANO

A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly and It allows hot magma, ash and gases to escape from below the surface.Volcanic activity is the most powerful force in nature. Some volcanic eruptions are much more powerful than the largest nuclear explosion. Volcanoes have killed thousands of people and caused some of the most frightening events in human history.

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface. Major types of volcanoes are as follows:

  • Shield volcanoes
  • Composite volcanoes
  • Caldera
  • Mid Ocean Ridge volcanoes

TYPES OF VOLCANOES

SHIELD VOLCANOES

A shield volcano is a type of volcano usually composed almost entirely of fluid lava flows. It is named for its low profile, resembling a warrior’s shield lying on the ground.

COMPOSITE VOLCANOES

These volcanoes are characterised by eruptions of cooler and more viscous lavas than basalt. These volcanoes often result in explosive eruptions. Along with lava, large quantities of pyroclastic material and ashes find their way to the ground. This material accumulates in the vicinity of the vent openings
leading to formation of layers, and this makes the mounts appear as composite volcanoes.

CALDERA

Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence and collapse rather than an explosion or impact when large-amounts of lava are released in a short amount of time.

Santa Ana Volcano.USAF.C-130.3figure – Caldera

MID-OCEAN RIDGE VOLCANOES

These volcanoes occur in the oceanic areas.There is a system of mid-ocean ridges more than 70,000 km long that stretches through all the ocean basins. The central portion of this ridge experiences frequent eruptions.

FAMOUS VOLCANOES AROUND THE WORLD

Sl NoVolcanoLocation Details
1Mount VesuviusNaples, Italy In AD79 (almost two thousand years ago!) it erupted. It was an explosive eruption, with no warning. Huge quantities of ash rained down on the city of Pompeii. The city and most of its residents were completely buried.
2KrakatoaIndonesiaIn August 1883, Krakatoa erupted with several huge explosions. The explosions were incredibly powerful, and destroyed most of the island. The sound of the explosions could be heard 5,000 kilometres away!
3Mount St. Helens VolcanoUnited StatesMount St. Helens is in the Cascade Range of mountains, which is found in Washington State, United States. Mount St. Helens was named after a British diplomat by explorer George Vancouver.In 1980, the volcano erupted, causing a huge amount of devastation.
4EyjafjallajökullIcelandCompared to other famous volcanoes, the Eyjafjallajökull eruption in 2010 was not particularly powerful. However, because it happened fairly recently, and affected a lot of people, it became very famous.It is dangerous for aeroplanes to fly through ash clouds, as ash can solidify on moving parts or clog up the engines.
5Mount PinatuboPhilippinesMount Pinatubo is on the island of Luzon in the Philippines. In June 1991 the volcano erupted violently. In fact, it was the second largest volcanic eruption of the 20th century.
6Mount EtnaItaly (Sicily)Mount Etna is the tallest active volcano in Europe. It is located in Sicily, a large island off of Italy (Sicily is the ‘football’ that the country of Italy looks like it is kicking on a world map).Mount Etna is the largest of Italy’s three volcanoes, and is over two and a half times as tall as Mount Vesuvius.Etna is a very active volcano, and has been erupting regularly for thousands of years. Recent eruptions in 2014 caused air traffic to be affected.
7Mount TamboraIndonesiaMount Tambora is on the Indonesian island of Sumbawa (Krakatoa is also in Indonesia). Mount Tambora famously erupted in 1815. It was one of the largest volcanic eruptions in history.The eruption affected the weather all around the world.
8Mauna LoaHawaiiHawaii has two famous volcanoes, Mauna Loa and Kilauea. Mauna Loa means ‘Long Mountain’ in Hawaiian, and Mauna Loa is the largest active volcano in the world.Mauna Loa does not erupt as violently as other volcanoes, but it does produce a large amount of lava. However, this is usually quite slow-moving (usually slower than walking pace).
9Mount PeléeWest IndiesMount Pelée is found on the island of Martinique in the West Indies. It erupted in May 1902, killing over 40,000 people, most of whom lived in the nearby city of St. Pierre. Most of the casualties were due to fast moving pyroclastic flows – hot gas and ash that flows from a volcano. One of the two people in St. Pierre to have survived the eruption was a murderer who was in the city’s prison
10CotopaxiEcuadorCotopaxi is a famous volcano in Ecuador. It is the second highest peak in the South American country, and one of the highest active volcanoes in the world. Cotopaxi is also one of, if not the, most active volcanoes in the world. Despite this, it is a popular mountain for mountaineers to climb.

VOLCANOES IN INDIA

NameLocationTypeLast eruptionDetails
Barren IslandAndaman IslandsActive Volcano2017Barren Island is an island located in the Andaman Sea, dominated by Barren Volcano, the only confirmed active volcano in South Asia, and the only active volcano along a chain of volcanoes from Sumatra to Myanmar.The first recorded eruption of the volcano dates back to 1787 . Since then, the volcano has erupted more than ten times, with the most recent one being in 2017.
NarcondamAndaman Islandsdormant volcano560 kyrs BPNarcondam is a small volcanic island located in the Andaman Sea. The island's peak rises to 710 m above mean sea level, and it is formed of andesite. It is part of the Andaman Islands, the main body of which lie approximately 124 km (77 mi) to the west. The name Narcondam could have been derived from the Tamil word naraka-kundam, meaning "a pit of Hell"
Deccan TrapsMaharashtra -66 myaThe Deccan Trapsare a large igneous province located on the Deccan Plateau of west-central India (17°–24°N, 73°–74°E) and are one of the largest volcanic features on Earth. The term "trap" has been used in geology since 1785–1795 for such rock formations. It is derived from the Scandinavian word for stairs ("trappa") and refers to the step-like hills forming the landscape of the region.
BaratangAndaman IslandsMud VolcanoActive since 2003Baratang Island is an island of the Andaman Islands. It belongs to the North and Middle Andaman administrative district, part of the Indian union territoryof Andaman and Nicobar Islands. Ranchiwalas Island is another name for Baratang Island.Baratang contains the only known examples of mud volcanoes in India. These mud volcanoes have erupted sporadically, with recent eruptions in 2005 believed to have been associated with the 2004 Indian Ocean earthquake.
Dhinodhar HillsGujaratExtinctInactive VolcanoDinodhar Hills are located near Nani Aral village, in Nakhatrana Taluka, Kutch District, Gujarat, in India. Dinodhar Hill is a tourist and pilgrimage spot. Dinodhar Hill, an inactive volcano rising to an elevation of 386 meters.
Dhosi HillHaryanaExtinct732 Ma BP (million years before present )Dhosi Hill is an extinct volcano, standing alone in the North-West end of the Aravali mountain range with height varying from about 345 to 470 meters from the surrounding land.It is part of Aravalli Mountain Range, that belongs to the Precambrian Malani igneous suite of rocks Dhosi Hill is located on the borders of the Indian states of Haryana and Rajasthan. The Haryana portion lies in Mahendragarh district to the south, 5 kilometres (3.1 mi) from Narnaul on Singhana Road; the Rajasthan portion lies in Jhunjhunu district to the north.
Tosham HillsHaryanaExtinct732 Ma BP (million years before present)Tusham hill old spelling), located at Tosham, with an average elevation of 207 meters (679 feet), and the rocks exposed in and around Tosham hills are part of subsurface north western spur of Alwar group of Delhi supergroup of Aravalli Mountain Range, belong to the Precambrian Malani igneous suite of rocks. The main Tusham hill is the second largest hill in the range. It has ancient rock inscriptions and rock paintings, paelo eroded rocky glacial channels and water cascades, and small hilltop lakes.

WORLD GEOGRAPHY COMPLETE NOTES

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