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We have discovered thousands of previously uncharted underwater mountains, which are also known as seamounts. They are included in the most detailed map of the ocean floor ever produced.

They were found by a team led by David Sandwell and Brook Tozer at the Scripps Institution of Oceanography in San Diego, California. Their new topographical map has uncovered more than 5000 new seamounts and possibly as many as 10,000. The exact number still needs to be confirmed, as they have not been counted individually yet.

The updated map, known as SRTM15+V2.0, will be valuable for climate modelling and tsunami prediction, for example to better understand ocean currents and underwater landslide risk.

Only about 10 per cent of the seabed has been mapped with sonar. The rest is mapped by measuring the effects of gravity on the sea’s surface.

Seamounts exert a greater gravitational force on the ocean than the flat seabed, which causes a slight difference in sea surface height. Satellites can accurately measure these differences to infer where seamounts exist.

Measurements like this were used for a 2014 map containing approximately 10,000 seamounts, but the new map uses more accurate data. For example, it uses data from the French-Indian AltiKa sensor, which was launched in 2013 and can measure the distance from the satellite it is on to the sea surface to within 21 millimetres – twice as accurate as previous instruments.

In 2014, we could map all the seamounts more than about 2 kilometres tall, today we can detect any taller than about 1.5 kilometres, says Sandwell.

He says thousands more seamounts are likely to  be detected after NASA’s SWOT satellite launches in 2021. SWOT should be able to find seamounts that are just 1 kilometre high.