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The Seashore

Rocky Shore Trail
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The Tides

This site uses tidal levels as a means of splitting the shore up into zones. For those not very familiar with Gaia's salty smock it will be useful to mention a few things about the cycles and patterns that occur.

The main cause of the tides is the Moon, the Sun has an effect as well. To find out more about this read on, otherwise go to Tide Diagrams for lots of relevant info.

The Moon's gravity causes the oceans to bulge out (tidal bulges) on opposite sides of the Earth simultaneously (email if you want to know why). We perceive these as high tides. Because of the rotation of the Earth on its own axis the tidal bulges slosh back and forth causing us to perceive high and low tides. There are roughly two high tides and two low tides every 25 hours. There's usually about 6 and a bit hours between high and low tide. This is the DAILY pattern

Because the Moon orbits the Earth, sometimes it's pulling in line with the Sun and sometimes it's pulling at an angle to the Sun. When it's pulling in line the tidal bulges are big. When it's pulling at an angle the tidal bulges are small. This produces the MONTHLY pattern

When the Moon is new or full it's in line with the Sun. When it's a half Moon it's at an angle to the Sun. This results in a monthly pattern as follows: New Moon: (No Moon visible in sky), Moon and Sun in line, bulges big, high tides extra high low tides extra low. These are called SPRING tides (nothing to do with the season)

Half Moon: (Roughly a week later), Moon and Sun at an angle, bulges smaller, high tides not so high low tides not so low. These are called NEAP tides

Full Moon: (Roughly a week later), Moon and Sun in line, bulges big, high tides extra high low tides extra low. These are called SPRING tides

Half Moon again: (Roughly a week later), Moon and Sun at an angle, bulges smaller, high tides not so high low tides not so low. These are called NEAP tides

New Moon: (Roughly a week later) No Moon visible in sky, Moon and Sun in line, bulges big, high tides extra high low tides extra low. These are called SPRING tides

Thus roughly speaking we get a week of spring tides followed by a week of neap tides followed by a week of spring tides followed by a week of neap tides. You do not of course jump from one to the other it's more in the nature of a steady change.

There is also a YEARLY pattern which we will mention very briefly:

Around the equinoxes (March 21st and September 21st) the spring tides are extra "springy" the highs are exceptionally high and the lows are exceptionally low. Correspondingly the neap tides at this time of year are extra "neapy" the highs are not very high at all and the lows are not very low.

Around the solstices (June 21st and December 21st) the spring tides are not so "springy" (higher and lower than neap tides but not greatly so) and the neap tides are less "neapy" (highs a bit higher and lows a bit lower than at other times of the year).

The reason for this are to do with the proximity of the Earth, Moon and Sun and the angle of the Moon's orbit about the Earth.

Remember this is a quick simplified explanation, over 400 variables are known to affect tides (luckily for you the author of this site is only dimly aware of most of them and does not propose to tell you about them (unless you email of course when we'll do our best to accommodate you)

All this has profound consequences for seashore creatures. Click here for a quick explanation.


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