The Movement of Tides

 by Siha Hoque

Hour by hour, the coastal landscape is continuously changing - due to the varying waves at sea. The advancing of the oceans (or sometimes rivers and lakes) on land and then receding is known as a tide. Tides are mostly described as high tide or low tide; where the body of water reaches either its maximum advance onto the shore or retreats as far back as possible. 

Tides are a very powerful tool in nature, they constantly and gradually erode our land, sculpting the shape of the solid matter we live on every second. They are measured by tide gauges. Our knowledge of tides and the currents of water surrounding them allow fishermen to make effective trips out to sea, and for us to even use the water as a renewable energy source for generating electricity.

Yet this phenomenon is the result of something much further from our oceans - the moon and Sun. The Sun and the moon's gravity may not be strong enough to tug the solid parts of the Earth off toward it, yet its distant pull is enough to influence the liquid on this planet. As the Earth rotates, the moon is nearest to different parts of it at a time, and this is always steadily changing. The side closest to the moon experiences the strongest attraction from it, and this causes the bodies of water on that side to rise up, forming a high tide. However, on the opposite side of the Earth the same thing happens too. This is due to the force made by the Earth rotating, that results in the accumulation of water from resistance: causing another high tide. The other parts of the planet and the water on them are left ebbing lower. 

Tide height changes frequently - one low tide may not be the same as the next. Throughout a month the tides may gradually increase to a maximum, and then lower to a minimum. Higher tides are called spring tides. They occur when the Earth, Sun and moon are all aligned - strengthening the total tide. When the Earth, Sun and moon form a right angle, a neap tide happens: here the high tides that would have been formed by the moon meet with the solar low tide, and partially cancel each other, producing an altogether lower tide.

Additionally, the three most common number of tide changes places can have in a twenty-four hour period are: diurnal tides - one high and low tide daily; semidiurnal - two highs and lows daily; and mixed semidiurnal tides - which is the same as semidiurnal but with a range of heights in tide. The type of tide each part of the world gets is also affected by the landscape as well as the depth of the area. Should the Earth have been a perfectly spherical shape entirely covered with water, the tides would match two smooth ripples travelling around it, exactly proportionate to each other. 

This means that over the millions of years, as the land mass gradually changed shape from a single continent - Pangea - the way the ocean moved did too. Today, the UK experiences semidiurnal tides, and as land continues to be worn away and deposited elsewhere, this may gradually change too.