Reaching the top of a mountain normally involves a steep climb, but these divers have gone the other way. They are part of a team mapping the Dacia and Tritón seamounts near the Canary Islands, off the north-west coast of Africa.
"These mountains could be considered as the 'other' Canary Islands, some of which, though now submerged, at one time rose up out of the sea," says Helena Álvarez, a marine scientist at Oceana, the conservation organisation behind the work.
In fact, they still are rising. A volcano near this crater is causing a new Canary Island to grow.
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