Secrets of the St. Lawrence

Baie des Sept Îles

- "Just look at those waves. And I thought we'd find calmer seas here. Let's get out of here right away."

Reflection

Live and learn! When waves strike a vertical barrier such as a cliff or a wharf, they are reflected and rebound.

But as they flow back out and meet incoming waves, their crests cross and build quickly, producing a choppy, confused sea up to a few nautical miles offshore. It's not very comfortable for anyone on board.

If you are mathematically inclined, you can use the formula opposite to draw up a chart showing how high the waves will build, depending on the fetch in Baie des Sept Îles.

Refraction

In such a confused sea, it wouldn't be wise to try to seek shelter near a cape or a point.

When waves approach shoals from an angle, they bend toward the shallows, increasing in height.

In the lee of an island, this refraction effect produces a cross sea. These confused and choppy conditions can make navigation very difficult and even dangerous, depending on the wind speed.

The same cross-sea effect can be produced by refraction when the shoal is an underwater mountain or point.