Deep underneath the ocean, there are swells that would put big wave surfers to shame. The biggest waves on Earth can’t be seen breaking against the shore, but underwater, they can reach heights almost as high as the tallest building in the Western Hemisphere, and can be observed throughout the year. 

Generated by tides pulling water across the varied topography of the ocean floor, as well as wind blowing across the water's surface, the largest documented waves in the world are in the eastern border of the South China Sea, which separates China and Vietnam from the Philippines. These underwater waves can reach heights of up to 500 meters (1640 feet). Unlike surface waves that crash over a period of seconds, they last for hours, growing larger as they move across the sea floor. 

As part of a new study published in Nature, a team of scientists dropped mooring lines with measuring instruments from buoys on the surface down to the ocean floor, observing the physics at play underwater. 

These massive underwater waves move marine life across the sea, allowing creatures to surf the tide into shore to feed or breed, a key activity in maintaining the South China Sea’s coral reef system. The mixing also serves to distribute heat from the surface of the water to the depths of the ocean. 

“It’s like a giant washing machine,” Thomas Peacock of MIT, one of the paper’s co-authors, said in a press statement. “The mixing is much more dramatic than we ever expected.”

[h/t: slashdot]