On 20th December 2021, the Tonga volcano began to erupt and on 15th January 2022, reached a peak which probably made it the largest volcanic eruption of the 21st century. It was reportedly as powerful as hundreds of atomic bombs! It also caused tsunami waves that wreaked havoc in Tonga and casued some damage in countries like the US, New Zealand, Chile and Peru.
The volcano was a part of what we call a volcanic arc(specifically the Tonga-Kermadec Islands volcanic arc). They’re a chain of volcanoes which are formed near a subduction zone, a place where the dense oceanic plates sink below the less dense continental plates. Water from the oceanic plate can lower the melting point of the oceanic crust and hence, it can melt easily to form magma under high pressures resulting from the oceanic sinking more and more below the continental plate.
When volcanoes erupt with such force, they can cause shockwaves, which are basically sharp fluctuations in air pressure/density which may travel at supersonic speeds and thus can even shatter glasses of nearby buildings. The amplitude of the shockwave in New Zealand was measured to be around 7 hPa(Pa is a unit of pressure. The normal atmosphere pressure is about 1 lakh pascals. So a 7hPa amplitude means a 7 % increase in pressure at that point )The shockwave from this eruption circled the globe 3-4 times! It was observed in Chennai, which is 12000 km away from the eruption site!
The volcano didn’t emit enough gases like SO_2 to cause a very drastic change in global climate. However, the people in the southern hemisphere can expect some peculiar changes in sunsets , such as purple sunsets ,for a few months after the eruptions.