Why Spring Tides Happen during the new and Full Moon

Spring tides are a type of tide that occurs twice a month. They are not to be thought of as only happening in the Spring as they are not named for this season but for the action of the tide. The term spring tide derives from the German word springen, meaning to jump or to leap up, just as the seas spring out and then spring back during these times of high high tides and low low tides.

What are tides?

Tides are the regular rise and fall of the sea’s waters and some lakes and rivers have tides as well. Water rises up over the shore and then retreats. When the rising waters reach their highest levels, it is high tide. Low tides occur when the receding waters have reached their lowest levels. Between these two tides is a flow of water known as an ebb tide. It flows from high tide to low tide. The Earth’s rotation, the Moon’s gravitational pull and to a lesser extent the Sun’s gravitational pull, are the primary tidal constituents, forces that contribute to the creation of tides.

Known as semidiurnal, Earth’s oceans mostly experience tides twice daily. The Old Farmer’s Almanac Tidal Glossary lists the different tidal ranges as follows:

Apogean tide, Diurnal, Mean Lower Low Water, Neap tide, Perigean Tide, Spring Tide, Syzygy, Semidiurnal and Vanishing Tide.

When do spring tides occur?

Spring tides happen twice a month, during the syzygies. Syzygy being the technical term used to denote the Sun, Moon and Earth’s alignment. This alignment is known as a New Moon when the Moon is in the middle and as a Full Moon when the Earth is in the middle. During these times, the Sun is exerting a gravitational pull on earth in combination with the Moon. Although the Sun’s force is only 46% as strong as the Moon’s, this combination nevertheless affects the tides. These tides, spring tides, will climb especially high and then fall to lower than low tides in the same day. This is due to the combined gravitational pull that causes the oceans to bulge. NationalGeographic.com explains:

“The tidal force exerted by the moon is strongest on the side of the Earth facing the moon. It is weakest on the side of the Earth facing the opposite direction. These differences in gravitational force allow the ocean to bulge outward in two places at the same time. One bulge occurs on the side of the Earth facing the moon. This is the moon’s direct tidal force pulling the ocean toward it. The other bulge occurs on the opposite side of the Earth. Here, the ocean bulges in the opposite direction of the moon, not toward it. The bulge may be understood as the moon’s tidal force pulling the planet (not the ocean) toward it.”

Are there different types of spring tides?

A few times each year a phenomenon called a perigee-syzygy occurs. Also known as a SuperMoon, this is when the Moon at its closest distance to earth in a given orbit (month), coincides with the full or new Moon. According to Fundyforce.ca, this spring tide, known as a perigean spring tide has the fastest water speeds and greatest tidal range among the tides.

Proxigean tides are rare perigean spring tides that coincide with the close proximity of Earth to the Sun, usually in December or January. These tides have had disastrous affects as almanac.com reports.