Surfers head to the Amazon to ride the Pororoca, one of the longest waves in the worldThe moon causes a tidal bore that reverses the flow of the river and slows the earth’s spin each day
These Brazilians are about to surf in a very unlikely place: the Amazon River. During full and new moons, a huge tide surges in from the Atlantic Ocean and reverses the flow of the mighty river, creating an enormous wave.
Called the “pororoca,” this nearly endless wave is an example of a tidal bore. The strongest tidal bores occur on the biannual equinoxes in September and March when the sun, moon and earth align, bringing the tides to their highest peak. Surfers flock to Brazil to ride one of the longest waves in the world, but they must be careful to dodge trees and even jungle animals that are caught up in the rushing water.
As the moon orbits the earth, gravity pulls the Earth’s oceans towards it creating tides and making our planet a little less round — more like the shape of a rugby ball instead of a sphere. At the same time, the pull slows down the earth’s rotation making each day just a tiny bit longer.
Watch the full story above. For more about the geological processes that affect our planet watch A Day in the Life of Earth on the Nature of Things.