Relevance: GS-1: Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone., geographical features and their location-changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes./GS-3: Environmental hazard and Disaster

Key phrases: volcanoes, Pacific ‘Ring of fire’ explosivity, fuel-coolant interaction’, caldera, lightining, meteotsunami, tsunami

Context:

• The Kingdom of Tonga doesn’t often attract global attention, but a violent eruption of an underwater volcano on January 15 has spread shock waves, quite literally, around half the world.

Background:

• The Hunga-Tonga-Hunga-Ha'apai volcano has erupted regularly over the past few decades. During events in 2009 and 2014-15 hot jets of magma and steam exploded through the waves. But these eruptions were small, dwarfed in scale by the January 2022 events.

About:

• The volcano, situated on an uninhabited island, became active in 2009.
• It consists of two small uninhabited islands, Hunga-Ha’apai and Hunga-Tonga, poking about 100m above sea level 65km north of Tonga’s capital Nuku’alofa.
• It lies along the Pacific ‘Ring of fire’, and is just over 60 kilom.etres from the island nation of Tonga.
• In the case of Tonga, the Pacific Plate was pushed down below the Indo-Australian Plate and Tonga plate, causing the molten rock to rise above and form the chain of volcanoes.
• Subduction zones are also where most of the violent earthquakes on the planet occur.

The Pacific ‘Ring of Fire’ or Pacific rim, or the Circum-Pacific Belt:

• It is an area along the Pacific Ocean that is characterised by active volcanoes and frequent earthquakes. It is home to about 75 per cent of the world’s volcanoes more than 450 volcanoes.
• Also, about 90 per cent of the world’s earthquakes occur here.

Volcano:

• A volcano is a land-form, a mountain, where molten rocks erupt through the surface of the planet. The volcano mountain opens downwards to a pool of molten rocks below the surface of the earth.
• When the pressure builds up in the earth’s crust, eruptions occur. Gasses and rock shoots up through the opening and spill over or fill the air with lava fragments. The volcano eruption can cause lateral blasts, hot ash and lava flow, mud-slides, and more.

Reasons for volcanic formations:

• Past events have unleashed city size rafts or pumice or seen volcanoes blowing themselves apart only to build new islands immediately afterward.
• This profusion of volcanoes exists because of the Pacific plate’s continuous dive beneath the Australian tectonic plate.
• As the slab descends into the superhot rocks of the mantle, the water inside gets baked out and rises into the mantle above. Adding water to these rocks causes them to more readily melt.
• This creates a lot of magma that tends to be sticky and filled with gas a potent recipe for explosive eruptions.
• Hunga Tonga-Hunga Ha'apai is no exception to this rule.

Why are the volcano’s eruptions so highly explosive, given that sea water should cool the magma down?

• If magma rises into sea water slowly, even at temperatures of about 1200 degrees Celsius, a thin film of steam forms between the magma and water.
• This provides a layer of insulation to allow the outer surface of the magma to cool. But this process doesn’t work when magma is blasted out of the ground full of volcanic gas.
• When magma enters the water rapidly, any steam layers are quickly disrupted, bringing hot magma in direct contact with cold water. Volcano researchers call this ‘fuel-coolant interaction’ and it is akin to weapons-grade chemical explosions.
• Extremely violent blasts tear the magma apart. A chain reaction begins, with new magma fragments exposing fresh hot interior surfaces to water, and the explosions repeat, ultimately jetting out volcanic particles and causing blasts with supersonic speeds.
• The 2014/15 eruption created a volcanic cone, joining the two old Hunga islands to create a combined island about 5km long. Along with a hidden ‘caldera’ 150m below the waves.
• The caldera is a crater-like depression around 5km across. Small eruptions occur mainly at the edge of the caldera, but very big ones come from the caldera itself. These big eruptions are so large the top of the erupting magma collapses inward, deepening the caldera.
• This demonstrates a huge explosive power, one that cannot be explained by magma-water interaction alone. It shows instead that large amounts of fresh, gas-charged magma have erupted from the caldera.

Why has this eruption produced what is likely to be a record-breaking number of discharges?

• The presence of water always ups the odds of lightning. When magma mingles with a shallow body of water, the trapped water is aggressively heated and vaporized, blasting that magma into millions of tiny pieces. The more plentiful and the finer the particles you have, the more lightning you generate.
• The heat of the eruption also readily transports water vapor into the colder, higher reaches of the atmosphere, where it becomes ice. That provides plenty of additional particles for the ash to collide with and generate electricity.

After effects:

• Activity on the 14th apparently removed approximately the middle third of the island that had been expanded over the previous few weeks.
• Large eruptions at Hunga Tonga-Hunga Ha'apai produced plumes that reached the stratosphere and caused significant regional effects.
• The atmosphere was blasted out of the way as a shockwave emanated from the island, radiating outward at close to the speed of sound.
• The shockwave itself triggered another big wave: The rapidly moving air impacting the ocean was powerful enough to force water to move out of the way, a phenomenon called a Meteotsunami.
• The eruption also produced a tsunami throughout Tonga and neighbouring Fiji and Samoa.
• The sonic boom was heard in parts of New Zealand more than 1,300 miles away, with the shockwave eventually traveling halfway around the world.
• As the volcano’s explosivity began to intensify, the amount of lightning emerging from its ashy plume began to eclipse not only that seen during this eruption, but during any eruption ever recorded.
• Ash fall containing Sulphur contaminated fresh water supplies, hindered sea transportation and harbor access, and caused flights to be cancelled.
• Most domestic and international communications on the islands were severed due to a break in an underwater cable, and ash fall has delayed both damage assessment and relief assistance.

Way Ahead:

• A relatively rare event: Such an explosion is thought to occur roughly once every thousand years. The hope is that the worst of the eruption is over.
• All these signs suggest the large Hunga caldera has awaken.
• Tsunami are generated by coupled atmospheric and ocean shock waves during an explosions, but they are also readily caused by submarine landslides and caldera collapses.
• It remains unclear if this is the climax of the eruption. It represents a major magma pressure release, which may settle the system.
• The reasons this eruption produced quite so much lightning are impossible to determine at present.

A warning, however, lies in geological deposits from the volcano’s previous eruptions. These complex sequences show each of the 1000-year major caldera eruption episodes involved many separate explosion events.

Hence we could be in for several weeks or even years of major volcanic unrest from the Hunga-Tonga-Hunga-Ha’apai volcano.

MainsQuestion:

Q. Volcanic eruption in Tonga has renewed the debate on the impact of climate change with special reference to small islands and their developments. Discuss along with measures taken in the recently concluded COP-26 with respect to small island nations.