Volcanism - class-IX

Sudden movements of the earth can be noticed during the eruption of a volcano. Sudden movements, caused by sudden endogenetic forces coming from deep within the earth, cause such sudden and rapid events that these cause massive destruction at and below the earth's surface. These forces work very quickly and their results are seen within minutes.

The highest active volcano in the world is Ojos del Salado on the Chile-Argentina border in the Central Andes. It rises to 6887 m / 22,595 ft. It has not erupted in recorded history but is an active volcano.

Volcanic crater is a circular depression in the ground caused by volcanic activity. It's typically a basin, circular in form within which occurs a vent from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of great depth.

Volcanic activity frequently occurs at the boundaries of the Earth's tectonic plates which are a series of large moving blocks. The movement of these plates plays a significant role in the type of volcano formed, which influences its shape. If the movement is smaller, they leads to volcanic eruptions. Larger movements may lead to earthquakes.

Aconcagua is the highest mountain outside Asia, at 6,961 metres and by extension the highest point in both the Western Hemisphere and the Southern Hemisphere. Aconcagua is of volcanic origin, but it is not an active volcano and cab be considered as extinct.

When a volcano ejects acid lava, they are loud and violent usually because of the explosive pressures building up in magma. They eject acid lava, ash, gases and rock fragments. They are dangerous as materials can rain down on settlements. Ex: Eruptions at Krakatoa in Indonesia.

Mount Kenya is the second highest mountain in Africa, after Kilimanjaro. Mount Kenya is a stratovolcano created approximately 3 million years after the opening of the East African rift. Before glaciation, it was 7,000 m high. It was covered by an ice cap for thousands of years. This has resulted in much eroded slopes and numerous valleys radiating from the centre.

An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.

An erupting volcano is an active volcano that is having an eruption...

A dormant volcano is an active volcano that is not erupting but supposed to erupt again.

An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.

The above classification is based on the frequency of eruption while the classification as a composite volcano is based on the structure of the volcano thus option C is the right answer.

Mt Vesuvius is a volcano located in Italy which had last recorded eruption in 1944, hence A is the correct answer. It has a long history of a number of eruptions in recorded history thus it is considered as an active volcano.

• Mt Kilimanjaro is a dormant volcano in Tanzania. Hence C is the correct option.
• It is also the highest mountain of Africa.

The number of potentially active volcanoes on Earth is estimated to be about 1500, with 550 of these having erupted in recorded history. The total number of volcanoes throughout the entire world is unknown because not all volcanoes are accessible, known and recorded.

• Barren Island is located in the Andaman and Nicobar group of islands in India. It is the only active volcano in India.
• Hence option C is correct.

A caldera is a large depression formed when a volcano erupts and collapses. During a volcanic eruption, magma present in the magma chamber underneath the volcano is expelled, often forcefully.

Volcanic materials of various sorts are ejected through a pipe and the vent situated at the top of the pipe. The enlarged from of the volcanic vent is known a volcanic crater and caldera.

Stromboli is one of the most active volcanoes on Earth and has been erupting almost continuously since 1932. Because it has been active for much of the last 2,000 years and its eruptions are visible for long distances at night, it is known as the "Lighthouse of the Mediterranean". It is among the world's most visited volcanoes.

Mount Etna is Europe's highest and most active volcano. Towering above the city of Catania on the island of Sicily, it has been growing for about 500,000 years and is in the midst of a series of eruptions that began in 2001.

Lava flows from the volcano. Molten rock materials are generally called magma below the earth's surface while when they come out at the earth's face they are called lava. Lava is very hot and the temperature ranges between 700 to 1200 degrees Celsius.

A volcanic crater is a funnel shaped hollow at the top of the vent. It is formed as lava and gas and ash are blasted upwards from the main vent. Material falls back down to earth around the vent and slowly piles up forming a rim around it. The inside of the crater is kept clear by the force of upward moving material constantly removing any debris which falls there.

Lava is the molten rock expelled by a volcano during an eruption. A lava flow is a moving/outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock. The term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties.

Magma is an extremely hot liquid and semi-liquid rock located under Earth's surface. Earth has a layered structure that consists of the inner core, outer core, mantle, and crust. Much of the planet's mantle consists of magma. When magma flows or erupts onto Earth's surface, it is called lava.

Barren Island is an island located in the Andaman Sea. It is the only confirmed active volcano in South Asia and the only active volcano along a chain of volcanoes from Sumatra to Myanmar.

There are no volcanoes on the Australian mainland that have erupted since European settlement, but some volcanoes in Victoria, South Australia, and North Queensland were witnessed by Aboriginal people several thousand years ago.

Molten rock located beneath the Earth's surface is called magma. Once it erupts onto the surface, it is referred to as lava.