Tides are the rise and fall of the ocean level. The gravitational pull of the Sun and the Moon, and rotation of the Earth are the main causes of tides. Below discussed are the different types of tides. One thing that must be noted is that the classification of tides may change from source to source.
The different types of tides
Places on Earth that are closest to the Moon at a given point of time experience a high tide. During a high tide, the ocean level rises and the water moves up on the shore to the maximum extent.
The moon exerts the gravitational force which pulls the water up causing high tides. The places which do not face the moon experience a low tide. During a low tide, the water recedes from the shore.
The side of the Earth opposite to the side facing the Moon also experiences a high tide. This is because of the centrifugal force generated due to the rotation of the Earth. The water accumulates on this side of the Earth causing a high tide.
The tidal range is the height difference between high tide and low tide.
Spring and Neap tides
Spring tides occur during the new moon or the full moon. During a spring tide, the gravitational pull of the Moon and Sun add up to create a tidal range greater than usual.
(New moon occurs when the Moon is between the Sun and the Earth. Full Moon occurs when the Earth is between the Sun and the Moon.)
Also read: The different phases of the moon
Neap tides occur when the direction of the Moon is perpendicular to the direction of the Sun. During Neap tides the tidal range is minimum.
Diurnal, Semidiurnal and Mixed tides
There are generally two high tides and two low tides each day on most parts of the Earth. When the two high tides (also the two low tides) have roughly the same height, the tides are known as semidiurnal tides. When the heights of the two high tides are not the same, the tides are known as mixed semidiurnal tides.
Due to the geography of the Earth, there is only a single high tide and a single low tide during a day in some areas. The tides in these areas are known as diurnal tides.