Welcome to brain Stuff production of I Heart Radio, Hey brain Stuff, Lauren vocal bomb. Here. The Alaskan coast is as dramatic as it is vast, and it spans over thirty three thousand miles or over fifty four thoud kilometers. U s State owes its very name to this sweeping ocean. Border. Alaska is an English language corruption of an Alouette term that, according to one translation, means the shore where the sea
breaks its back. And if you drive out to a place called turning in Arm in the Gulf of Alaska at just the right time, you get to watch some aquatic action that's pretty spectacular. The turnig In Arm Waterway is a northern branch of the cook Inlet that cuts into the Greater Anchorage area. Here, the water normally flows out toward the inlet, but shortly after low tide waves move in the opposite direction and travel upstream, and these waves can be epic in scale. The biggest waves are
up to ten ft or three meters tall. This is a well known example Boar tides also known as tidal bores or just boars, and riding them has become a rite of passage for many surfers in the Pacific Northwest. While this phenomenon has been seen at numerous locales around the world, it requires a very specific set of conditions. But before we dive into those, it might be a good idea to go over some basic tidal science. By
and large, tides are gravity's handiwork. Due to the gravitational influence of our moon plus the inertia of our movement through space, the ocean is always bulging out a bit on opposite sides of the planet. While Earth rotates, it passes through these tidal bulges. That means your favorite seaside beach will experience high tide when it enters each bulge, and low tide as it travels between them, So plan
your sandcastle contests accordingly. Because Earth finishes a new rotation around its axis once every twenty four hours, most coastal areas witness two high tides and two low tides per day, but there are loads of exceptions. The layout of continents, islands, and peninsulas impedes tides in certain places. Parts of the Gulf Coast, for example, only see one daily set of high and low tides. No matter where you are, though, the tides will vary in strength from day to day
all over the world. During full moons and new moons, when the Earth, moon and Sun are arranged in a straight line, high tides are especially high and low tides are really low. We call these extreme tides spring tides, which, despite the name, occur all year round, not just in the springtime. But let's turn back to turn Agin Arm. Although it's shallow and narrow, the Turnigin feeds into a broad bay, namely cook Inlet. On this wide expanse, the difference between high and low tides, i e. The tidal
range can be stark. The cook inlets water level at high tide maybe thirty five ft or ten and a half meters higher than it was during the preceding low tide, and these are exactly the ingredients needed to produce tidal bores. After a low tide on cook Inlet, water funnels into the herning In Arm, generating boar waves that barrel inland, sometimes traveling at speeds up to twenty four miles per hour.
That's nearly thirty nine kilometers per hour. Since bores only happen when the circumstances are just right, not all waterways that touch the Ocean can get them. In total, there are eighty or so rivers around the globe that undergo tidal bores. The phenomenon tends to be at its most dramatic during spring tides, whereas the turning in Arm has twice daily bore tides. The Amazon River only receives bores
on the days of new and full moons. Once the spring tides arrive, water from the Atlantic comes charging up the Amazon River, temporarily reversing its natural flow. Waves generated by this process have been known to journey about five hundred miles or eight hundred kilometers inland, called porta rocca. The Amazon bars attain considerable size, measuring upwards of thirteen feet or four meters tall in some cases. The strongest portor roca events of all take place every year on
the equinoxes. To prepare for these surges, local residents move their boats and livestock safely away from the Amazon. Accidents do still happen, though Jacques Cousteau once lost a boat to pororoca waves while filming in South America. Title boars impact ecosystems wherever they occur. Trees, rocks, and river bottom sediment get pushed around by the waves, and those aren't the only things they churn up. Down in the Amazon, current reversals can leave stunned or dead animals floating in
the water, attracting hungry piranhas. Strong boars are also prone to eject fish from rivers, stranding them on beaches or launching them into the air. That's why Alaskan bald eagles, Australian sharks, and Malaysian crocodiles like to scavenge in the wakes of title boars. Big boars attract humans as well.
Sal Domingo Stolkapim, a community that borders the Amazon, has been hosting the Brazilian National Poroca Surfing Championship since n Alaskan wave chasers flocked the turning in arm shortly before or after every spring tide when the boars are at their largest. Oh and there's one last thing we should mention about boar tides. They roar. The waves produce a great deal of turbulence, wildsplacing sediment, scraping up shoals, and
unleashing loads of air bubbles. Add all those sources up and you've got a recipe for thunderous low frequency booms that can be heard over vast distances. Today's episode was written by Mark Bancini and produced by Tyler. Playing brain Stuff is a production of I Heart Radio's How Stuff Works. For more on this and lots of other swell topics you know, visit our home planet, how stuff Works dot com.
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