Throughout the past week, every time I would finish working and go towards the beach where I usually freedive, I would be disappointed to see that there is no beach available. Not because of the tourist crowds, but because the sea would cover it all. On the other hand, when going to work, I would see extensive land masses covered with nothing else than algae patches and sea urchins. The reason for this phenomena are the Sun and the Moon interacting forcefully with the Earth.
Let’s get back to the school days, when we would learn about gravitational force in Physics classes. Two bodies attract each other by gravitational forcing, which is directly proportional to the product of their masses and inversely proportional to the square of the distance that separates the masses. The gravitational forces of attraction that occur between the Earth and the Moon, and between the Earth and the Sun, create tidal energy, which will vary depending on the positions of these bodies.
The gravitational force of the Moon is stronger than that of the Sun because the Moon is much closer to the Earth. It causes the oceans to bulge in two opposite sides of the planet, which can be seen as two water masses continuously undulating. In some parts of the world, the undulation is much more variable than in others, especially in those areas where the water can move quickly and without constraints.
It is possible to observe the tidal movement almost twice a day, as the time between the first high tide and the second is around 12 hours and 25 minutes. When the tide goes up, it is usually called flood tide, while the opposite – change from high to low tide – is called ebb tide. A higher tidal range occurs around the full and the new moon. During these phases, the Sun, the Moon and the Earth are aligned, meaning that the pulling force is at the highest. These tides are known as king or spring tide. On the other hand, when the moon is waxing or waning, descending or crescent respectively, the tidal range is the lowest because the Moon is not aligned with the Sun and the Earth. The tides in these cases are called neaps.
In addition to the influence of the Moon, there is also a seasonal influence. In spring and autumn, the Sun and the Moon are aligned with the equator, and these phenomena are known as spring and autumn equinoxes, respectively. Therefore these periods of the year hold the highest tidal ranges.
On Thursday (September 17th, 2020) there was the new moon, which aligned in between the Sun and the Earth. Together with the Sun, the force pulling the Earth increased causing the first series of autumn equinox tides. According to tradition, these tides arrive approximately at the same time as the celebration of the Virgin of Pino occurs in Teror, a city in the greener part of Gran Canaria. In fact, the equinox tides are usually called mareas de Pino by the locals and it marks the end of the summer.
The phenomena of Pino’s tides produces high swells thanks to many factors, such as the wind and atmospheric pressure. However, cyclones from the Caribbean rise up to the United States and cross the Atlantic Ocean under the form of storms, which create high waves that reach the Canary Islands and are awaited especially by surfers. To say the least, the water takes nutrients and minerals by eroding the sandy beaches. In doing so, it nourishes the marine ecosystems and cleans the beaches at the same time.
Hopefully, now you understand better that the science behind tidal fluctuations is quite complex. I must admit that I haven’t even touched on all what is behind. But at least now you will be able to explain to your friends what happens daily and seasonally to our oceans.
Hammons, T.J., 1993. Tidal power. Proceedings of the IEEE, 81(3), pp.419-433.
Amin, M., 1979. A note on extreme tidal levels. The International Hydrographic Review.