Last updated: September 28, 2021
Article
How Tides Work at Acadia
Ever wonder how the ocean can go from deep to shallow in only a few hours?
The requested video is no longer available.
This happens every day at Acadia National Park. The cyclical rise and fall of the seas are called tides. But how do they occur? The story of tides starts between 225,623 and 252,088 miles away - on our Moon.
Courtesy of Sardius Stalker
The Tides are Turning: How the Moon's Gravity Impacts the Earth
It might sound like lunar-sea, but the Moon’s gravitational force on the Earth is so powerful that it causes tidal fluctuations of around 8-12 feet here in Acadia!
It is commonly understood that the Moon orbits the Earth due to the Earth’s gravitational force. Yet, our Moon exerts a gravitational force right back! Even though the Moon has 80 times less mass than the Earth, the Moon’s gravitational force changes the shape of our planet. This force is stronger on the side of Earth closer to the Moon than the side opposite. How this force manifests as ocean tides may not be quite what you’d imagine...
Courtesy of NASA
How Tidal Forces Change the Earth’s Shape
As the Earth rotates on its axis and revolves around the Sun, the side of the Earth that faces the Moon bulges outward. It's almost as if the Earth were reaching towards the Moon. The bulge doesn’t just appear on one side, but on both, turning our world into a giant oval. We call this phenomenon tidal force.
Why do These Bulges Occur?
A few reputable scientific theories explain the bulges in different ways.
One theory suggests that the tidal force is a kind of pulling exerted by the Moon on the Earth. Land doesn’t move a whole lot - only a few centimeters or so - but oceans can be sucked out quite far. As the Moon’s gravitational pull ultimately creates bulges on the ocean water closest and farthest away from it, the Earth spins on its axis. High tides are experienced where the water balloons out and low tides occur in between these bulges. Most coastlines experience two high tides, two low tides, and everything in between as the Earth rotates through the two oceanic bulges each day, which are always pointed exactly towards and exactly away from the Moon.
Courtesy of NOAA
A second theory suggests that instead of a pulling action toward the Moon, the mechanism producing the tides is more of a squeezing toward Earth’s core. As the tidal force bares down on the Earth, the ocean on the sides closest to and furthest away from the Moon bulge out.
Either way, the result is that our Earth always looks like a football!
Yoda is Almost Right
Yoda counseled Luke Skywalker, “Size matters not.” In many ways, this is true. Proximity is often a bigger factor than size or mass when it comes to gravity. The Sun is a great example. Though the Sun is about 400 times larger than the Moon, it exerts much less tidal force on the Earth than the Moon. Why? The answer has to do with distance. The Sun is about 400 times farther away from the Earth than the Moon, and this great distance weakens the Sun’s tidal force. If the Moon were to disappear tomorrow, the Sun would still cause tides on Earth. However, the tides would only be about 1/2 of the size they are today. But don’t discount this hot ball of glowing gases just yet...
Teamwork Makes the Dream Work
When the Sun and the Moon align, they create extra-large tidal ranges known as spring tides. Spring tides, pictured below, have nothing to do with the seasons, and occur twice a month at the new and full Moon. Because the Sun and Moon are aligned during a spring tide, it’s like they are on the same tug-of-war team, pulling the Earth’s oceans towards them.
Courtesy of Kat Gardiner
But the Sun and the Moon are not always aligned. During the first and third quarter Moon, the Sun is at a right angle to the Moon. A slightly lower high tide, and a slightly higher low tide, result. These milder fluctuations, pictured below, are called neap tides.
Courtesy of Kat Gardiner
How do the Tides Impact Us?
Here at Acadia National Park, life on the coast relies on the rhythmic flow of salt water as it surges out and drifts in. Rock crabs wave their claws to ward off hungry herring gulls during the low tide buffet, and breadcrumb sponges soak up plankton and oxygen as the water rushes back in. Seaweed floats up and spreads out with the incoming tides, and blue mussel shells snap closed as the tide ebbs in and out, in and out, all day long.
NPS/Crystal Lewis
When we visit these tidally influenced areas, we must explore with respect for these creatures and our own safety in mind. Given that tidal fluctuations at Acadia reach about 12 feet, it is very important to pay attention to the high and low tide so that you stay safe. Hikers that ford their way to Bar Island during the 3 hours in which the land bridge emerges must be careful not to get stuck as the tide rises. Canoers and kayakers can exhaust themselves paddling against the tides. Those brave enough to swim in the chilly Sand Beach waves should keep their eyes peeled on the goings-on of the ocean. Also please keep in mind that at Acadia National Park there are two high tides and two low tides every day. The timing of the tides constantly shifts, moving forward about 50 minutes every 24 hours. This is because the Moon revolves around the Earth a little bit faster than the Earth rotates on its axis. Given the complexity of the tides and their drastic impact on the environment, it is imperative for your safety that you consult a tide chart prior to recreating on, in, or around the ocean.
Though tides can be very complicated, they are a special part of life here at Acadia National Park. And remember, just as Yoda says, “the (tidal) Force will be with you always.”