9. WET AND DRY

Tides are caused by the gravitational pull of the moon and sun on the water in the sea.  As the earth changes positions around the sun and the moon goes around the earth the strength of the pull varies. 

The pull is largest when the sun and moon are in line with the earth at full moon and the new moon (dark) the tides then are spring tides.  The spring tides are when tides are highest and lowest.  The neap tides are not very high or very low.

Text Box: See what else you can find out about tides in our area from an annual tide chart -- How high are the highest tides in the year? How low are the lowest tides in the year?

 

 

 

This graph shows the tide heights in our area for July 1987.  Only every second day is marked.


In light pencil create a grid by joining the day marks at top and bottom
of the graph.  Then join the height marks from one side to the other.

  1. How many high tides every day?  (remember the graph is marked every 2 days) 

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  2. Colour the spring tides red and the neap tides blue.


  3. For a blue snail living above 1.8 metres what days would it be wet by the tide?

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  4. For a seaweed growing at 0.3 metres what days might it get left out of water?

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Nature Coast Marine Group November 2008