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Name: Shasta
Status: Educator
Age: 30s
Location: N/A
Country: N/A
Date: June 25, 2003

I understand the differences between diurnal, semidiurnal, and mixed tides, but what causes different areas to experience the varying tides?
If, the earth was a perfect sphere with no continents then all we would experience would be our diurnal tides.
Why is this?
Does it have something to do with different continent shapes? I really must know.


The tide at a particular location along the shore is heavily influenced by the slope of the sea bottom that the water has to flow over and the size and shape of the inlet (for a river delta or outlet) that it flows into. Places like the Bay of Fundy in Nova Scotia or the Inchon Bay in South Korea, narrow and slope upward rapidly as they go inland, causing some very high tides. Areas along a coastline with a gently sloping sea bottom have smaller tides.

So, yes, the shape of the land area, as well as of the sea bottom figure into the height of the tide. Furthermore, the longitude needs to be considered, as the far western end of a bay will experience high or low tide later than the entrance to the bay (this can even be delayed significantly past what it would be if there were no land mass because of the shear difficulty of moving that much water so great a distance), and vice versa for a bay that extends inward to the east.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory

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