A Beginners Guide to Tides
In this detailed guide we give you all the understanding you need about tides..
How many tides are there in a day?
The majority of the world will see two tides each day or within a 24 hour period. Two high tides and Two low tides. There is a period of 6 hours and 12.5 minutes between a high tide and a low tide.
Example: High tide is at 12pm – the next low tide will be at 6.12.5pm (6 hours and 12.5 minutes) or there is a high tide every 12 hours and 25 minutes. So for instance, if it’s high tide at 12pm today, the next high tide will roughly be at 12.50pm the following day.
As both the sun and the moon have an effect on the earth’s tides we can split these two forces into separate days for the ease of understanding the effect of each.
In a solar day, it takes the earth 24 hours to orbit around the sun.
Unlike a solar day, a lunar day takes 24 hours and 50 minutes to make its full rotation of its axis. This is longer because the moon revolves around the earth in the same direction as the earth rotates on its axis. Because of this, the earth takes longer to catch up to the moon’s rotation. i.e 50 minutes.
The moon and the sun affect the earth’s tides on a daily basis and follows a monthly lunar cycle and is why we are able to predict the tides in advance. A common misconception about tides is that the ocean only moves in one direction, towards the side of the earth that is closest to the moon. If this was the case there would only be one high tide and one low tide in each 24 hour 50 minute period.
In reality, the part of the earth that is both closest to the moon and furthermost away from the moon will receive high tides within a 24 hour 50 minutes period, whilst other areas of the earth will then see a low tide.
This is because water is being pulled towards the moon on one side of the earth and the earth pulled away from the water on the other side of the earth, creating a bulging effect and a high tide at opposite sides of the earth.
What is a high tide?
A high tide is when the ocean is at its fullest point on the beach. On the beach, we notice that there isn’t much sand to walk on and the waves are breaking close to the shore or at the top of the beach. A high tide is caused when the moon is overhead or at its closest to the earth and when it is at its furthermost away.
What is a low tide?
A low tide is caused when the ocean is at its lowest point of the beach. On the beach, we notice that the sea is far away and leaves a large patch of sand once covered at high tide exposed. Low tides are caused when the earth is a right angles to the moon.
Spring tides –
As well as having high tides and low tides each day we see a variation in the size of these high tides and low tides. This again is due to the rotation of the earth and each phase of the lunar cycle that we pass dictates the size of the tides.
What is a Spring tide?
A spring tide or king tide can be defined as high high tides and low low tides or large tidal movement between one tide and the next. If you are surfing or at the beach during this phase of the lunar cycle you will notice a big difference between low tide and high tide.
What causes spring tides?
You’ll notice a spring tide occurs when there is a full moon and/or a new moon. When the sun and the moon are aligned (both on the same side of the earth) that makes the gravitation pull very strong creating high high tides and low low tides.
What is a Neap tide?
A neap tide is where we don’t see much difference between low tide and high tide. The tidal range is smaller than of a Spring tide. Neap tides occur when we see a waxing and/or waning moon. This occurs twice every month when the sun and the moon are at right angles to each other the solar tide partially cancels out the lunar tide making for a small tidal range.
Sublunar tides – this is when the moon is directly over a specific point on the earth and the moon’s gravity pulls water towards the moon.
Antipodal tides – this is when the moon’s gravitational effect on a particular spot on the earth is at its weakest. i.e when the moon is furthermost away or opposite side of the earth from the ocean.
How do tides affect the surf?
The tide will affect the surf in a variety of ways. Waves are formed as the energy or swell in the ocean moves from deep water to shallow water and is forced upwards, waves will then peak and start to break as the hit sand banks or reef that make up the bathymetry of the sea floor. The volume of water that covers these sandbanks or reefs will effect how quickly the waves form and break.
Bathymetry – is the shape of the sea floor
Waves at high tide are said to be fat and slow ,or lumpy due to the large amount or volume of water that is sitting over the sand banks or reef on that particular beach.
Waves at low tide are said to be quick, steep or dumpy, this is because there is very little water sitting over the sand bank or reef allowing the ocean swells to travel from very deep water straight into very shallow water.
Every beach is different: All beaches have a different topography which causes the waves to form and break. Some beaches suit a high tide where some may suit a mid or lower tide.