Walloping waves.

Sailors have long told tales of 10-story-tall waves rising from calm seas. Now, scientists have finally proved these walls of water exist.

Using satellites (objects orbiting Earth that send and receive signals), the European Space Agency snapped pictures of the ocean surface for three weeks. Scientists analyzed the images to detect rogue waves (waves much larger than surrounding waves). They spotted 10 waves over 25 meters (82 feet) tall.

Turns out, the giants often appear near strong ocean currents. There, smaller swells may combine into an oversize wave, says Wolfgang Rosenthal, a wave scientist at Germany's GKSS Research Center.

Rosenthal hopes to better predict where and when the ship-sinkers occur. Then, sailors can avoid wave-prone areas. Here's to smooth sailing.