The "Ring of Fire" is an ominously-named belt of active volcanoes that skirts around the Pacific basin for some 40,000 kilometres.
It lies on the boundary between the Pacific Plate and a number of other tectonic plates. It is home to about 75 per cent of Earth's active volcanoes, and is the origin of about 90 per cent of earthquakes.
The underwater volcano Hunga Tonga-Hunga Ha’apai, which sent a tsunami hurtling towards Tonga following a massive eruption on Saturday, is unsurprisingly found within the Ring of Fire.
Volcanologist Heather Handley, an adjunct associate professor at Monash University, said volcanoes within the Ring of Fire often had more "explosive potential".
"It is a string of largely-underwater volcanoes related to tectonic activity, where we get two plates pushing together.
"This forces one plate underneath the other, and in these regions we get a lot more gas-rich magma. And that gas-rich magma has more of an explosive potential than somewhere in say, Hawaii, where there is less gas trapped in the magma."
There is the potential for this gas-rich magma to react violently when it comes into contact with the surrounding cold sea water.
Although official estimates measuring the size of the Hunga Tonga-Hunga Ha’apai eruption are still being calculated, early data suggests the towering gas plumes were between 20 and 30 kilometres high.
The energy released in the eruption has been compared to 1,000 Hiroshima bombs.
A team of scientists observe the volcano on 14 January, a day before its violent eruption. Source: Tonga Geological Service
Dr Handley said it was difficult to predict how the volcano would behave following the blast, but further eruptions could be on the cards.
Volcanologist Dr Chris Firth said it was one of the world's largest volcanic eruptions since the 1990s.
"The volcano appears to have quietened for now, however eruptions of this magnitude are not usually over so quickly and the volcano may continue to be active over coming weeks or months."
What next for Tonga?
While the immediate tsunami threat caused by the explosion has receded, it will take some time before the longer-term impacts can be assessed.
"The ash from the eruption can affect drinking water supplies – particularly for places such as Tonga that rely on rainfall as a drinking water source," Dr Handley said.
"All the gases that are carried by the ash - fluorine, chlorine, sulfur - these can leach into drinking water."
The eruption also released large amounts of sulfur dioxide gas. New Zealand's National Institute of Water and Atmospheric Research described sulfur dioxide as a "toxic, invisible pollutant".
"In Tonga, possible short-term hazards to human health include acid rain and 'volcanic smog'," NIWA said in a statement.
Other impacts could include ash smothering crops and polluted air causing breathing problems.
It has been difficult to assess how hard Tonga has been hit because communications links were disrupted by the blast.
However, aid agencies such as Save the Children are already scrambling to secure drinking water, food and first aid supplies.
"The experts have warned that volcanic activity may continue causing new tsunami warnings to be issued, and recommended people stay indoors to avoid the ash and smoke," Shairana Ali from Save the Children Fiji said in a statement.
The full extent of the damage in Tonga is still unclear with communication lines down. Source: Dr Faka’iloatonga Taumoefolau/Twitter
Lord Fatafehi Fakafanua, the speaker of Tonga's legislative assembly, on Monday morning said a number of areas had been hit by heavy ashfall.
"On January 15, 2022, following an unprecedented volcanic eruption, a devastating tsunami struck the Kingdom of Tonga. Many areas were also affected by substantial volcanic ashfall," he said in a statement.
"Communications remain down and the full extent of the harm to lives and property is currently unknown.
"What we do know is that Tonga needs immediate assistance to provide its citizens with fresh drinking water and food."
