YOUNG: There are places in the American landscape that are unlike anywhere else in the world, places that stand out, grab the memory like no other. We’ve been chronicling some of these unique natural features in our periodic series: Home Ground: Language for an American Landscape. This week, writer Eva Saulitis brings us her definition of a rare … and sometimes exciting phenomenon known as the Tidal Bore.

SAULITIS: Tidal bore. A term coined by seamen around 1600, tidal bore describes a violent wall of water rushing up a shallow narrowing river, estuary, or bay. Bores, also called bore tides, form when an incoming tide meets a particular geography a resistance: sand, silt bars, narrowing channels and heaps water up to 15 feet high moving inland at 10 to 15 miles per hour.

Most bores build after low water of a spring tide, the year’s biggest tidal flux. Famous bore tides occur in the Truro River in Canada’s Bay of Fundy and at Turnagain Arm in Alaska’s Cook Inlet. The latter driven by a tidal rise of 30 feet in six hours.

In summer, travelers driving along Turnigain Arm can witness wind surfers bundled in dry suits dancing along the waves face. Their brightly colored sails a dramatic contrast to the gray silty inlet. When it surges up the lower Amazon the bore, pororoca can shave forests and destroy homes. It is greatly feared by locals yet ridden by elite surfers from around the world.

YOUNG: Eva Saulitis is a writer, teacher and marine biologist from Homer, Alaska. Her definition of “Tidal Bore” appears in the book Home Ground: Language for an American Landscape edited by Barry Lopez and Debra Gwartney.