It is likely that you have ever witnessed on a beach or coast how the sea can rise and fall a few meters. What is the reason for this? Would you like to understand why the tide rises and falls? The answer is found in the two stars closest to our planet: the Sun and the Moon.
What are the tides
We start this article by defining the concept of tide . Tides are regular or periodic variations in sea level of the order of several meters and are caused by the gravitational force of attraction jointly exerted by the Moon and the Sun on the Earth. This change in sea level occurs at intervals of approximately 6 hours and, in addition, there are several types of tides, as we will see later.
In addition to the tides that affect the waters of seas and oceans , there are other types of movements that occur periodically and for the same reason. They are the tides that occur in the atmosphere (with changes of several kilometers) and in the lithosphere (with small variations that can hardly be perceived).
We continue this article by explaining how tides are produced . As already indicated, the cause of the tides is the gravitational force exerted by the moon and the sun . In other words, these two stars attract water from seas and oceans to each other, modifying their level.
Now, Newton’s law of gravitational attraction tells us that this force depends on the mass of the bodies and also on the distance that separates them. In this way, although the Moon is much smaller than the Sun, the attraction it exerts on the Earth is much greater than that of the great solar star (between two to three times more). This is because the Moon is much closer to our planet than the Sun. Therefore, the Moon and the tides have a strong link , the lunar tides (that is, those caused by the Moon) being more important in amplitude than those that the Sun may cause.
But there is still more, because according to the different positions that both stars have with respect to our planet, different types of tides can be produced, since the gravitational pull will be different in each case. It is also relevant to comment that the flattening of the Earth (since it is not a perfect sphere) varies with this tidal phenomenon (remember that three-quarters of the planet’s surface is covered with water).
As we have already anticipated, there are different types of tides and they are classified based on various criteria. Depending on the height that the sea water reaches, the tides can be of two types:
- High tide or high tide: when the sea reaches its highest level, we will have high tides, which occur approximately every 12 hours.
- Low tide or low tide: when the height of the sea reaches its lowest level we will have low tides, which also occur approximately every 12 hours.
Therefore, since the low tides and high tides have a periodicity of 12 hours , both occur alternating in an interval of 6 hours. Likewise, when we have high tide in one part of the globe, there will be a low tide just in the opposite part.
The following classification of the types of tides is according to the phases in which the Moon is :
They occur when we have a Full Moon and a New Moon , since it is in these lunar phases when the Sun and the Moon are aligned , allowing a greater gravitational effect to be achieved. Spring tides are, therefore, the largest.
They occur when the moon is in the phases of waning and waxing , since it is in these phases when the two bodies are in opposing points ( at an angle of 90to each other) and offset their attractive forces . Neap tides are therefore the smallest.
Consequences of the tides
Have you ever wondered about the effects of tides ?
- It is well known among fishermen that when there are high tides, a larger quantity of fish is usually caught . Plus, it’s even easier to fish when low tides add up.
- It is also convenient for divers and surfers to know about the types of tides and when they will occur in order to plan their activities.
- In addition to changes in the depth of the water , it is also important to know that the tides can produce uncontrollable currents that can influence the speed and course of the vessels, as well as cause some person to be unfortunately dragged into the interior of the vessel. ocean.
- Another consequence of the tides is that they are capable of generating the ideal conditions for the specific ecosystem of the intertidal zone. It is an ecosystem that is adapted to both marine and aerial conditions, with typical fauna such as some mollusks , crabs , starfish and sea anemones. Among the flora we can find various species of algae.
How to tell if the tide is high or low
How can you know if a low or high tide is happening at sea when we are observing it? To find out, it is appropriate that you take into account the periodicity of which we have spoken previously, as well as the phase in which the Moon is at that moment.
In addition, a very clear indication that the tide is going out is the fact that we see traces of foam and other residues . Without forgetting, of course, that we can find specific flora and fauna of the intertidal zone.
However, with a simple Internet search, you can find specific tide tables for each area that will give you an answer to this question.
Finally, if you are looking for an answer to why there are no tides in seas like the Mediterranean and there are in other seas such as the Cantabrian, we will tell you below. Although the Moon is capable of attracting huge bodies of water , its gravitational force is not as effective with smaller bodies of water, such as that of the Mediterranean Sea.
However, it cannot be said that there are no tides, but that these are not so powerful or appreciable . If, for example, the tides of the Cantabrian Sea are one and a half meters, those of the Mediterranean may only reach 50 centimeters, but this phenomenon also occurs .