What is the difference between high tide and low tide?
Do tides affect how waves break?
In this detailed guide we answer all of these questions and more to give you all the understanding you need about tides.
The tides that shape our coastlines play a huge part in how and when we deliver our surfing and coasteering activities here in Newquay Cornwall.
What are tides?
Tides are caused by the gravitational pull of the moon and sun, and as we all know we have high tides and low tides.
A way to get one’s head around the process of tides is to think of a massive, slow moving wave created far, far out at sea that travels gradually towards the coastlines with every ebb, flow and cycle of the moon.
The moon and the sun do not have an equal gravitational effect on the tides, with the moon counting for roughly 2/3rds of the gravitational pull as opposed to 1/3rd from the sun.
Although we experience a stronger gravitational pull in our day to day lives from the sun than that of the moon, the tides are not generated by the strength of gravity but instead by whats known as gravitational gradient. Since the moon is closer to the earth it exerts more gravitational gradient than the sun and so has a stronger effect on the world’s oceans.
Despite the moon being smaller, it is much closer to the earth so it exerts greater gravitational gradient over our oceans. This is why you would have heard of the connection between the tides and the moon.
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. Lunar day:
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.
For our surf lessons in Newquay we typically avoid running lessons within 1 hour before, during and 1 hour after a high tide. When the tide is full or high this typically causes the waves to break close to the beach which we find doesn’t always create the best conditions for learning to surf.
Many people that join us for a Coasteering session are surprised that we cannot deliver Coasteering sessions any given time of day. Typically the most popular Coasteering session will involve a mixture of elements such as wild swimming, low-level traversing, and deep water cliff jumps.
With many folks interested in challenging themselves to a cliff jump Coasteering companies in Cornwall need to keep a close eye on the tidal movement in their area each day to ensure that there is enough water for customers to plunge into.
Never attempt to go Coasteering without a local professional Coasteering provider
Here in Newquay, our high tides are usually in the morning or late afternoon, this makes for some fantastic still early morning or classic sunset Coasteering experiences.
What is tidal range or coefficient?
Tidal range or coefficient refers to the distance between a high tide and a low tide and is measured in meters.
surgewatch.org refers to it as: Tidal range is the vertical difference in height between consecutive high and low waters over a tidal cycle.
The tidal range will change slightly each day due to local weather conditions and as the cycle of the moon moves around the earth from neaps tides to spring tides.
When reading the tide times or surf forecast this is shown as 6.2 or 5.7 in the middle column after the morning high tide or low tide time. The higher the figure, the greater the coefficient or tidal range that day. As we know this is directly related to spring or neap tides.
When we refer to “how big the tide is” this is in reference to the coefficient or tidal range on that particular tide. Not the distance that the sea has travelled up or down the beach.
What is Chart datum?
Chart datum is the highest or lowest astronomical tide possible or the highest or lowest point that the tide is expected to rise or fall under average meteorological conditions.
This level then sets a bench mark for tidal movement. All tidal movement is measured above the lowest astronomical tide and below the highest astronomical tide and is used in part to map out minimum or maximum depths of coastal waters.
One of the points in the UK that chart datum is measured is Newlyn in Cornwall. In the UK we measure chart datum as a figure of zero. Rising tides will then measure how many meters above zero or chart datum that particular tide will rise or fall.
American chart datum is taken from a mean or average low or average high tide. This means that you can often get negative tides during spring tides and bad weather.
Congratulations if you made it here!
Although a very investing topic, truly understanding the the process behind tidal patterns takes quite the explanation.
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