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Secrets of the St. Lawrence

The wind and the waves - Graveyards


- "Now, listen to this. If the waves start getting steeper when you're close to shore, watch out. You're approaching shoals. Be particularly cautious of waves breaking at the mouth of a river."


The numerous shoals along the shore and near islands can often be traps. When the waves reach the shallow water, they slow and begin to tumble and break.

There are 2 types of situations: in the first, the bottom rises gradually and so do the waves; in the other, the bottom rises abruptly, as is often the case at the mouth of a river.

In the second case, the waves will break suddenly and form a line of surf. Mariners need to watch out for the underlying bar of alluvial deposits built up over the centuries. Underwater cliffs produce the same effect.

Shoaling - As the water depth grows shallower near shore the wave heights become taller and wave lengths become shorter.


If the depth of the bottom is at least half the wavelength, the waves will be able to flow smoothly over such shoals.

If the depth of the bottom is less than that, the waves will become steeper and may tumble into breakers.

Out in the open sea, mariners need to watch out for banks. They will cause the sea to behave the same way.

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