(INTRO SEQUENCE)

On Canada's eastern coast, tucked between the provinces of New Brunswick and Nova Scotia, lies the Bay of Fundy, a 270 kilometer-long body of water that is home to one of the strangest daily occurrences on Earth. It has the largest tidal range in the world. While the average difference between high tide and low tide is about 1 meter throughout the world, water levels in parts of this bay rise and fall by fourteen meters.

Over the course of six hours and thirteen minutes, the average time between each high and low tide in the Bay, tides move more than 160 billion metric tons of water. That's more than the combined flow of all the world's rivers put together. So, what exactly is going on here, and is there a way to harness all that energy?

We know that the gravitational pull of the moon--and, to a lesser extent, the sun--is responsible for creating the tides, but the daily phenomenon in the Bay of Fundy results from a perfect confluence of conditions that exaggerates the tides' effects, particularly the Bay's size and shape with a heavy-duty dose of really excellent timing. The Bay of Fundy is essentially a huge, earthen basin, and any liquid in the basin will rhythmically slosh back and forth once it's set in motion. It's called seiching--there's a whole word for it--sometimes oscillation, and it happens in most confined bodies of water, like lakes and bays, but the speed at which liquid oscillates depends on how long and deep the basin is that's holding it. As water oscillates, the surface will rise at one end of the basin, then at the other side, and then back again. In a bathtub, you may have noticed it takes a few seconds for water to oscillate in a single cycle, but in the Bay of Fundy, it takes about twelve and a half hours, which coincides almost exactly with the cycle of the tides as the waters of the Atlantic Ocean enter and leave the bay.

So, essentially, the natural oscillation of Fundy's water corresponds with, and is reinforced by, the tides. The effect is a lot like giving a couple of extra pushes to a kid on a swing: one push from behind when they're swinging forward, and an additional nudge in the opposite direction when they're headed back. And the shape of the Bay helps amplify this effect as well. Fundy's topography is kind of like a funnel, becoming both narrower and shallower in its northern portions, which helps force the water higher onto the shore.

Now, the movement of such huge volumes of water conveys an incredible amount of energy, and slowly, we're learning how to harness that energy, thanks to a tidal power plant in the Bay of Fundy that's only one of three such plants in the world. The power plant consists mainly of the kind of gated dam called a barrage that's built across an inlet of the Bay. When the tide comes in, the gates let the water flow into a huge reservoir. At high tide, the gates close, and that stored water is run through a system of turbines that spin to generate electricity.

But the barrage setup is particularly inefficient, and a host of marine wildlife, including a couple of whales, have been known to get trapped in the reservoir, so the next generation of tidal energy in the Bay of Fundy will include tidal turbines anchored to the ocean floor. They'll use the movement of flowing water to generate electricity in the same way that wind turbines use moving air, but because water is about eight hundred times more dense than air, tidal turbines don't have to spin as fast.

Since this whole phenomenon in the Bay of Fundy is driven mostly by the gravitational action of the moon, you might think of this useful byproduct of the tides as lunar power. In any case, it's just one more way in which the world is uniquely awesome.

Thanks for watching the SciShow dos. If you'd like to help us keep exploring the world, go to subbable.com/scishow to find out how you can become a supporter. And if you want to keep getting smarter with us, don't forget to go to youtube.com/scishow and subscribe.