“The bore tide is a huge wave or series of waves that advance down Turnagain Arm in a wall of water up to 10-feet high. It’s a dramatic show of nature’s power that’s easy to see using our guidelines below.
The bore tide is a rush of seawater that returns to a shallow and narrowing inlet from a broad bay. Bore tides come in after extreme minus low tides created by the full or new moon.
Bore tides occur all over the world—there are around 60 of them—but only a few are large enough to make a name for themselves. One in China, for example, stretches almost 30 feet tall and travels more than 20 miles per hour. Alaska’s most famous bore tide occurs in Turnagain Arm, just outside Anchorage. It climbs up to 6 – 10 feet tall and can reach speeds of 10 to 15 miles per hour. It takes not just a low tide but also about a 27-foot tidal differential (between high and low tide) for a bore to form in Turnagain Arm.”
Original Article: http://www.alaska.org/advice/alaska-bore-tide