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A tidal bore (or just bore) is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travel up a river against the direction of the current. As such, it is a true tidal wave (not to be confused with a tsunami).
Bores occur in a relatively few locations worldwide, in areas with a large tidal range, only on certain tides, and when an incoming tide is funnelled into a shallow, narrowing river via a broad bay. A bore is a natural example of a self-reinforcing solitary wave or soliton. Larger bores can be particularly dangerous for shipping, but also present a challenge to surfers.
The word bore derives through Old English from the Old Norse word bara, meaning a wave or swell.
Rivers that have been known to exhibit bores include:
- Amazon River, up to 4m (12 feet) high, running at up to 25 km per hour (15 miles per hour). It is known locally as the pororoca.
Tidal bore on the Petitcodiac River
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