Context

• Two major volcanoes Mauna Loa in Hawaii and Mount Semeru in Indonesia — erupted in a span of a week, releasing plumes of gases such as carbon dioxide (CO2) and sulphur dioxide (SO2) into the atmosphere. 

Key Facts

• In 2022, the world recorded 25 new volcanic eruptions, according to the Global Volcanism Program, a database distributed by Smithsonian Institution. In 2021, 33 new eruptions occurred.
• One study simulated SO2 emissions from over 90 volcanoes. Roughly 3 teragrams of SO2 was released per year on an average in the last decade.
• SO2 reacts with water to form sulphuric acid droplets, which become part of aerosol particles. 
  • Aerosols are tiny liquid droplets suspended in the air. The sulphur aerosols can scatter and absorb incoming sunlight.
• Human contribution to the carbon cycle is more than 100 times those from all the volcanoes in the world combined, the US National Aeronautics and Space Administration (NASA) estimated. 
• In contrast, human activities such as fossil fuel burning and cement production released 36.3 gigatonnes of CO2 into the atmosphere in 2015, according to the Global Carbon Budget 2016.
• About 99 per cent of the gas molecules emitted during a volcanic eruption are water vapour, CO2 and SO2.

Why do volcanoes erupt?

• The deeper one goes under the surface of the Earth towards its core, the hotter it gets. The geothermal gradient, the amount that the Earth’s temperature increases with depth, indicates heat flowing from the Earth’s warm interior to its surface. At a certain depth, the heat is such that it melts rocks and creates what geologists call ‘magma’.

  

• Magma is lighter than solid rock and hence it rises, collecting in magma chambers. Chambers which have the potential to cause volcanic eruptions are found at a relatively shallow depth, between six to ten km under the surface. As magma builds up in these chambers, it forces its way up through cracks and fissures in Earth’s crust. This is what we call a volcanic eruption. The magma that surfaces on the Earth’s crust is referred to as lava.

Effusive volcanoes and Explosive volcanoes

• In effusive volcanoes, magma flows with less resistance, allowing gases to escape easily, the British Geological Survey noted.
• In explosive volcanoes, magma erupts rapidly out of the volcano as pressure builds. They can give rise to pyroclastic flows, which contain rock fragments and gases moving downhill under gravity. They have a temperature range of 200-700 degrees Celsius and can destroy everything in their path.

Why are some volcanic eruptions explosive and some not?

• While the typical image of a volcano is that of a fountain of lava spouting high in the air from the mouth of the volcano, eruptions vary in intensity and explosiveness, depending on the composition of the magma.
• In simple terms, runny magma makes for less explosive volcanic eruptions that typically are less dangerous. Since the magma is runny, gasses are able to escape, leading to a steady but relatively gentle flow of lava out of the mouth of the volcano. The eruption at Mauna Loa is of this kind. Since the lava flows out at a slow pace, people typically have enough time to move out of the way. Geologists are also able to predict the flow of the lava depending on the incline and exact consistency it has.
• If magma is thick and sticky, it makes it harder for gasses to escape on a consistent basis. This leads to a build-up of pressure until a breaking point is reached. At this time, the gasses escape violently, all at once, causing an explosion. Lava blasts into the air, breaking apart into pieces called tephra. These can be extremely dangerous, ranging from the size of tiny particles to massive boulders.
• This sort of eruption can be deadly: as thick clouds of tephra race down the side of the volcano, they destroy everything in their path. Ash erupted into the sky falls back to Earth like powdery snow. If thick enough, blankets of ash can suffocate plants, animals, and humans. Further, when the hot volcanic materials mix with nearby sources of water, they can create mudflows that have been known to bury entire communities alive. Mount Vesuvius, which obliterated the city of Pompeii, is an example of an explosive volcano.
• The Volcanic Explosivity Index (VEI) is a scale used to measure the explosivity of a volcano. It has a range of 1 to 8 with a higher VEI indicating more explosivity. While the VEI of the current eruption at Mauna Loa is not known yet, the previous eruption in 1984 was deemed to have a VEI of 0. The highest VEI ever recorded in Mauna Loa has been 2 (in 1854 and 1868).

Some famous volcanoes

• Any volcano that has erupted within the Holocene period (in the last 11,650 years) is considered to be “active” by scientists.
• “Dormant” volcanoes are those active volcanoes which are not in the process of erupting currently, but have the potential to do so in the future. Mauna Loa was a dormant volcano for the last 38 years.
• “Extinct” volcanoes are ones which scientists predict will never face any further volcanic activity. Ben Nevis, the tallest mountain in the UK, is an extinct volcano.
  • Krakatoa, Indonesia
  • Mount Vesuvius, Italy
  • Mount Fuji, Japan
  • Eyjafjallajökull, Iceland
  • Kīlauea, Hawaii
  • Mount St Helens, USA

Reference: IE & DTE

Visit Abhiyan PEDIA (One of the Most Followed / Recommended) for UPSC Revisions: Click Here

IAS Abhiyan is now on Telegram: Click on the Below link to Join our Channels to stay Updated 

IAS Abhiyan Official: Click Here to Join

For UPSC Mains Value Edition (Facts, Quotes, Best Practices, Case Studies): Click Here to Join