Scientists from the Scripps Institution of Oceanography have discovered 19,000 seamounts formed by volcanic eruptions on the ocean floor, Science Alert reports.. The height of such mountains can reach 3-10 kilometers..

They can usually be found using sonar, but only if the ship passes directly over them.. Mountains less than two kilometers high are even harder to spot because they form near ocean ridges..

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For decades, scientists have been using satellite data to find small bumps on the surface of the sea and map them.. While sonar uses sound waves that ricochet off the seafloor to map its features, satellite altimetry does so indirectly by measuring small changes in sea surface elevation that reflect the gravitational pull from mounds in the Earth's underwater crust.. The larger the embankment, the more its gravitational pull pulls seawater from above.

Using this method, the scientists discovered an additional 19,325 underwater volcanoes, adding them to the 24,643 mapped seamounts that the two team members had previously cataloged back in 2011, and correcting some errors in the process..

This brings the total number of known seamounts to 43,454, almost twice as many as previously known..

Many of the recently discovered seamounts are smaller and thought to be too small to be detected by satellite data.. The height of the smallest volcano found is 421 meters, and the largest is 2500 meters..

Previously, scientists said that a volcanic eruption in the resort of Santorini is inevitable. The last time it erupted in 1650, then 70 people died..