The underwater volcano that erupted so spectacularly off Tonga is fuelled by the tectonic movements on the floor of the Western Pacific.

As the Pacific plate is subducted beneath the Australian plate at a rate of 120cm (47in) a year it takes with it vast quantities of sediment and water.

The five-mile thick plate is drawn deep beneath the seabed and once it gets to about 100km down a chemical reaction involving the water and sediment begins.

Liquid is pushed upwards into the near-solid mantle, which is melted into magma by the force of the process and this is itself driven upwards over time. Despite being estimated to be about 100 to 200 metres beneath the surface of the sea, the volcano erupted with such force that gas and lava were shot into the air.

Volcanoes in the Ring of Fire tend to spew out huge quantities of gas, including carbon dioxide and sulphur dioxide, with the lava.

The low sea pressure associated with shallow depth and the sudden cooling that takes place when the molten lava reaches the water means that the lava fragments and turns into pumice, which forms the new island.

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