Wicked High Tides are Coming to Boston!
This fall, Boston will experience a spectacular tidal event: the Perigean Spring Tides (also called King Tides). These “wicked high tides” result in high tides that are 2-4 feet higher than normal. This natural phenomenon occurs a few times each year, and gives us a window into how sea level rise will soon start affecting our daily lives.
What causes Perigean Spring Tides?
To understand exactly what’s causing these wicked high tides, there are three important things to know:
High and low tides are caused by the pull of gravity from our neighbors, the Sun and Moon – Because it’s a liquid, water is very susceptible to the pull of gravity from the Sun and Moon. This pull causes the oceans to bulge out where the Sun and Moon are closest. As the Earth spins, we actually rotate inside of the bulge, and we experience changing tides! Because the Moon is so much closer to Earth than the Sun, its pull is much stronger – that’s why the tides are strongly linked to the phases of the moon.
The Moon’s orbit around the Earth isn’t a perfect circle – It’s actually oval-shaped, which means some months the Moon is closer to the Earth than others. When the Moon is closest to the Earth, it’s in “perigee,” or is “perigean.” That means its pull on our oceans is even stronger than normal. (If you’ve ever heard of a “super moon,” that’s when the moon is both full and perigean, so it appears extra-large in the sky!)
When there’s a new or full moon, the Sun, Moon, and Earth line up, and the “pull” of the Sun and Moon on our oceans combines to make an extra-high tide – These are called “spring” tides, because the tide springs or jumps higher than usual.
When there is a new or full Moon and the Moon is in perigee, we experience wicked high tides!
