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Ask Sam: Why Are Tides So Different From Place To Place?

Photo by Jonathan Combe,

Every other Friday on Morning Edition, Outside/In host Sam Evans-Brown tackles a question from a listener. This week, we're buzzing because...

...Patty from Northampton asks: "I should understand the tides but I really don't. So in North Hampton, we have a very small beach even at low tide. And I was recently at Ogunquit beach with a friend, and the tide goes the way the heck out at low tide. And I don't know why!"

Note: This edition of Ask Sam originally aired in October, 2019.

So first off, readers probably know that the tides are cause by the gravitation pull of the moon and the force of the Earth's rotation. These two forces cause our oceans to sort of 'bulge out' on two sides, and thin out on the others. The bulges, as they slosh across the globe, are actually called "tidal waves", which have little to do with the image of a tsunami that you might have previously associated with the phrase. 

These are large forces of course  - so why should the tides differ so much from beach to beach? The answer has to do with the underlying regional geography. While the tide may rise an identical number of feet from one beach to another (if they're a relatively short distance away) the horizontal distance the tide travels can be greater or shorter depending on the shape of the coastline. If the underlying slope of a coastlines is steep (as it may be in North Hampton) it may not look as dramatic as it does in Ogunquit, where the coastline rises more gradually.

Additionally, the underlying topography can make tides slosh differently in different places, as it crashes against underwater obstacles, or enters narrow channels. Consider the Bay of Fundy in Canada, which has made it's astounding tidessomething of a tourist attraction.

Credit Courtesy of Will Verafong, Flickr CC.

Sam Evans-Brown has been working for New Hampshire Public Radio since 2010, when he began as a freelancer. He shifted gears in 2016 and began producing Outside/In, a podcast and radio show about “the natural world and how we use it.” His work has won him several awards, including two regional Edward R. Murrow awards, one national Murrow, and the Overseas Press Club of America's award for best environmental reporting in any medium. He studied Politics and Spanish at Bates College, and before reporting was variously employed as a Spanish teacher, farmer, bicycle mechanic, ski coach, research assistant, a wilderness trip leader and a technical supporter.

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