Context:
The eruption of the biggest mountain on the island of Java in Indonesia – Mount Semeru killed at least 14 persons and left dozens injured.
Relevance:
Prelims, GS-I: Geography (Physical geography, Volcanoes, Important Geophysical phenomena), GS-III: Disaster Management
Dimensions of the Article:
- About Mount Semeru
- Stratovolcano
- About the Ring of Fire
About Mount Semeru
- Mount Semeru is an active volcano in East Java, Indonesia.
- It is located in a subduction zone, where the Indo-Australian plate subducts under the Eurasia plate.
- This stratovolcano is also known as Mahameru, meaning “The Great Mountain” in Sanskrit. Semeru is named after Sumeru, the central world-mountain in Hinduism.
- Semeru’s eruptive history is extensive. Since 1818, at least 55 eruptions have been recorded (11 of which resulted in fatalities) consisting of both lava flows and pyroclastic flows.
- Semeru has been in a state of near-constant eruption from 1967 to the present.
Stratovolcano
- A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra.
- Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas.
- The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity.
- The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma.
- Stratovolcanoes are sometimes called “composite volcanoes” because of their composite stratified structure built up from sequential outpourings of erupted materials.
- They are among the most common types of volcanoes, in contrast to the less common shield volcanoes.
- Two famous examples of stratovolcanoes are Krakatoa in Indonesia, known for its catastrophic eruption in 1883, and Vesuvius in Italy, whose catastrophic eruption in AD 79 buried the Roman cities of Pompeii and Herculaneum.
- In modern times, Mount St. Helens in Washington State, USA and Mount Pinatubo in the Philippines have erupted catastrophically, but with fewer deaths.
About the Ring of Fire
- Many volcanoes in the Ring of Fire were created through a process of subduction. And most of the planet’s subduction zones happen to be located in the Ring of Fire
- It is a string of at least 450 active and dormant volcanoes that form a semi-circle, or horse shoe, around the Philippine Sea plate, the Pacific Plate, Juan de Fuca and Cocos plates, and the Nazca Plate.
- There is a lot of seismic activity in the area.
- 90 per cent of all earthquakes strike within the Ring of Fire
Why are there so many volcanoes in the Ring of Fire?
- The tectonic plates move non-stop over a layer of partly solid and partly molten rock which is called the Earth’s mantle.
- When the plates collide or move apart, for instance, the Earth moves, literally.
- Mountains, like the Andes in South America and the Rockies in North America, as well as volcanoes have formed through the collision of tectonic plates.
- Many volcanoes in the Ring of Fire were created through a process of subduction. And most of the planet’s subduction zones happen to be located in the Ring of Fire
What is subduction?
- Subduction happens when tectonic plates shift, and one plate is shoved under another.
- This movement of the ocean floor produces a “mineral transmutation,” which leads to the melting and solidification of magma – that is, the formation of volcanoes.
- Basically, when a “downgoing” oceanic plate is shoved into a hotter mantle plate, it heats up, volatile elements mix, and this produces the magma.
- The magma then rises up through the overlying plate and spurts out at the surface.
-Source: The Hindu
