Tides are one of those things that are very simple to explain on one level and very difficult on another. As a first-year student in college who came to Maine from Missouri, I had no personal experience or understanding of tides. I was confused by the fact that the ramp leading down to the sailing dock was much steeper one day than it had been on another. My marine biology professor explained the concept of tides with a simple, hands-on demonstration that has stuck with me. She chose two students with long hair and asked them to take out their ponytails. Then, they faced each other, held both of each other’s hands and spun around. Their hair swung outward as did their bodies.

The force they were demonstrating was a centrifugal force as the earth turns and their hair was akin to the oceans that bulge out on either side of the earth as a result. None of this would happen, however, without another force – gravity. Both the sun and the moon exert a gravitational force on the earth. Because each body exerts a pull on the other, when they are all in alignment, their forces combine, and the pull is the greatest. This is the case during a full moon – and the reason why tides are extra high at that point in the moon’s cycle.

In reality, there is a lot more to tides than centrifugal force and gravity. These other factors determine the average high and low tide levels. Jonathan White’s book, Tides: The Science and Spirit of the Ocean, describes the breadth of these factors and also some amazing examples throughout the world. One of the more influential is the formation of the land around the water. Canada’s Bay of Fundy, home of some of the world’s largest tides, is a deep narrow bay. Because of the shape of the bay, when the tide rushes in, it gets funneled into a small area and essentially piles up in what is called a tidal bore which causes a very big rise in water level. The difference between high and low tide here can be 40 feet or more. It’s strange to stand on a pier nearly four stories above mud where you once stepped off onto a floating boat.

The tidal range in Casco Bay falls between these two extremes with an average tidal range of about nine feet. That’s still nothing to ignore and can be a big problem if you don’t anticipate it and find yourself running aground or, conversely, your boat floating away. The other place this change in water level can cause big impacts is along the shoreline. Where there are particularly gentle slopes, there are times when high tide can bring water up over bridges and roads.

This brings up another couple of important factors that impact tidal height, the first of which is storms that can both add more water to the mix and increase the movement in the water to result in higher tides. As conditions change in our oceans and planet, there have been changes in weather patterns that have increased the frequency of these storms. In addition, there have been worldwide increases in ocean water levels due to the melting of glaciers that otherwise lock-up this liquid water in the form of ice.

We often hear about changes in sea level and their impacts on other places in the world where there are more inhabited low-lying land areas. But you can see these changes in Casco Bay as well. A photographer friend who is a volunteer for the Friends of Casco Bay’s Water Reporter program shared these drone photographs comparing an unusually high tide (11 ½ feet) at the beginning of November with a more typical high tide as an illustration of a local example of this. He is one of many volunteers along the coast that have been documenting what these super high tides look like for Friends of Casco Bay, a local non-profit that works on an array of issues including monitoring the impacts of climate change in the bay.

There is much to be learned about the connectivity between ocean and land and how they may not be as separated as they seem. Seeing what these high tides look like and how much they change our familiar landscape is an opportunity both to learn more about how tides work and to consider how changes in the ocean affect us onshore.

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