Scientists have discovered the true ferocity of a huge volcanic eruption off the coast of Tonga in January.

When the underwater mountain erupted, it sent ash and water-vapour half-way to space, and generated tsunami waves across the globe.

A survey by New Zealand and UK vessels has now fully mapped the area around the Pacific volcano.

It shows the seafloor was scoured and sculpted by violent debris flows out to a distance of over 80km (50 miles).

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