What Causes Tides-Moon?
Gravity of moon and sun pulls up the water in ocean but the Moon influences the tides most.When moon pulls up the water it creates two bulges. One bulge is directly under the moon and one on opposite side of earth,because earth turns these bulges move around the earth. When there is no bulge it is low tide and when there is a bulge it is high tide.All over earth there is a high tide and low tide on earth twice a day.
The shape of the sea bottom also influences the pattern .In the pacific ocean there is no land ,the difference is only a few centimeters. In between France and England all the water is forced through a narrow channel. This causes a huge difference between Calais and Dover.
The rotation of earth also has a direct impact on tides. The rotation of earth causes whirlpool around certain points of the ocean
Patterns of Tides
The shape of the sea bottom and the whirlpool current alters the simple pattern.
There are three different patterns of tides
There are semi diurnal tides: Two high tides and Two low tides , both equal in height
There are diurnal tides: one high tide and one low tide
There are mixed tides ,two high and Two low tides-,unequal in height.
Effect of Sun
The Sun also creates two bulges on either side of earth but the bulges are smaller.At certain time of the month the bulges of the moon and sun line up
Types of Tides
This happens at full moon and new moon. At full and new moon high tides are extra high and low tides are extra low, we call it a spring tide.
When the sun and moon works against each other tides are smallest,we call this a neap tide
When there is a big difference between low and high tide there is a lot of water movement. There will be strong ocean currents.
Whanganui River at Pipiriki, December 2014 © Liz Charpleix 
