February 11th, 2016
Posts Tagged ‘what causes tide to change’
If you think the tide is a just a laundry detergent, you might need a little more help besides this here article. But if you’re like a lot of people out there, you probably just have a couple of simple questions that I can hopefully answer below. I’ll start from the beginning, not to insult your intelligence, but instead to make sure that everyone can follow along and fully understand why the oceans do what they do.
What is the tide?
First off, tide is a general term used to refer to the daily rise and fall of the Earth’s oceans (and other large bodies of water) caused by the external gravities of the sun and the moon.
As the Earth spins in orbit, both the moon and sun tug furiously at the planet as it makes its rounds in space. Since the world’s bodies of water aren’t “bolted down” as are the rocks and mountains on the Earth’s crust, these waters shift and flow depending on the movements of the moon and sun (I know, technically it’s the Earth movements and not the sun’s Mr. Copernicus, but you get my drift.)
Because these external forces of gravity are so great, not only do the oceans bulge out in the direction towards the sun and the moon, but they also want to bulge out in the opposite direction. The result is an almost footbal like bulge of the oceans when the gravities are aligned. That’s because the Earth is pulled by each of these gravities so forcefully that the planet itself displaces water on the opposite side.
So that is why every 24 hours, or 1 full rotation of the Earth, there are generally 4 different high and low tides at your local break. However in some places these tide patterns do vary because of obstructions caused by the Earth’s large landmasses, but we won’t bore you with those diurnal-mixed-semi-diurnal tide nuances.
Why are some tides higher or lower than others? What causes the tide’s height to change?
FACT – Your highest and lowest tides will normally occur during Full and New Moons.
While I’d like to tell you that this is because of some weird werewolf superstition type thing, it’s really just because this is when the sun and moon’s gravities are aligned as they tug at the Earth. This special gravitational alignment creates what Oceanographers call Spring tides (And no, this has nothing to do with the season Jump to Conclusions Mat!) Spring tides are your most extreme tides meaning really high highs and really low lows.
However when the moon is in first & third quarter phases (or half full if you’re an optimist), the tide changes are relatively minor in comparison. That’s because the moon and sun pull at an almost right angle and create relatively equal amounts of force on all sides. Remember the football comparison I mentioned earlier? Well these two “footballs” cancel each other out. The result is a Neap Tide or a relatively minor change between high and low tides. See Below Pic for Clarification.
So depending on the distance and the orientation of the moon, the higher or lower the tides will be. For those of you visual learners below is a simplified animation, that’s obviously not to scale, but should explain everything above.
How does the tide affects the surf?
To understand this question let’s first take a look at waves. Waves are built up energy from wind that travel across the ocean like ripples in a pond. Without a reef, sandbar or shoreline, waves would never break at all. Not until the bottom of a wave is slowed down by the sea floor, does it acualy start to pitch and create something to ride.
So enter the tide. As the sea level rises and falls, waves will hit the coast in either deeper or shallower water causing it to break differently.
Since the bottom topography, or bathymetry, is different for every location, the tide will affect every spot differently. However, below are some generalizations that will hold true provided that the break gets considerably deeper during a high and shallower during a low.
During a high tide waves generally have more water in between them and the bottom and tend to spill over and onto themselves causing mushy or slower waves. i.e. the dreaded mushburger. That’s because there is less resistance at the bottom of the wave to slow it down enough and create a decent face.
High Tide Push:
During an incoming tide (low to high) you may hear the term High Tide push. This is when waves tend to become larger and more powerful with the added “push” from the incoming tide.
Shorebreak Caused by High Tide:
Aside from mushy waves, sometimes a high tide will make the surf miss all the bottom contours completely and cause the waves to pitch right over and onto the sand. This happens at many beaches where there is a steep drop off into deep water. Many call this type of surf shorebreak or shorepound and it can be very dangerous to an unsuspecting beach goer.
Conversely during a lower tide waves tend to hit shallower areas that slow the bottom portion of the wave down much quicker and can cause the top of the wave to pitch over itself and barrel. See below picture.
Low tides, especially extreme ones, can expose reefs, tide pools, and sandbars. This can be hazardous to unexperienced surfers (as waves will break with less cushioning for falls), but can be great for free-divers (can dive to deeper areas with less effort), fishermen (can cast out to further depths from shore), or anyone who wants to check out everything onshore that was underwater 6 hours earlier.
During low tides many people like to check out tidepools, or pockets of water left behind in rocks by the outgoing tide. A full ecosystem of intertidal critters are usually exposed at rocky beaches during low tides.
Tracking the Tide
Since the moon and Earth move in predictable motions, oceanographers are able to accurately predict the tide height and times for beaches well in advance and all over the world. While you can find this info online, or in a tide book, one of the easiest and best ways to track the tide is with a specialized tide watch.
Tide watches come with varying degrees of information and can help you predict the tide for your local break. A personal favorite of mine are the Nixon tide watches.
These watches are especially popular among surfers because they’re fairly inexpensive, they are no bigger than your average wristwatch, and they contain pre-programmed tide information for 200 beaches until 2020. With the special tide functionality on the Nixons you can track general tide height, future tides, and exact high & low tide times, among a number of other functions you’d normally find on a wristwatch.
Aside from the Nixons, we carry a number of other great tide watches on our site that can be equally helpful.
So whether your a surfer wanting to know if the waves will get better/worse, a fisherman looking for the best time to cast out, or just your everyday beach lover, it’s always good to know what the tide is doing at any particular moment. So get yourself a tide watch, learn how to use it and you will be glad you did. If not you might end up as that oblivious kook doing the “yard sale” when the incoming tide washes away his belongings.. I mean, at least that’s entertaining for the rest of us!Thank you for visiting the Swell blog. Visit us on www.facebook.com/swell for more exclusive fan offers, giveaways and more.