Speaker 1: Welcome to brain Stuff production of I Heart Radio, Hey
Speaker 1: brain Stuff, Lauren vocal bomb. Here. The Alaskan coast is
Speaker 1: as dramatic as it is vast, and it spans over
Speaker 1: thirty three thousand miles or over fifty four thoud kilometers.
Speaker 1: U s State owes its very name to this sweeping ocean. Border.
Speaker 1: Alaska is an English language corruption of an Alouette term that,
Speaker 1: according to one translation, means the shore where the sea
Speaker 1: breaks its back. And if you drive out to a
Speaker 1: place called turning in Arm in the Gulf of Alaska
Speaker 1: at just the right time, you get to watch some
Speaker 1: aquatic action that's pretty spectacular. The turnig In Arm Waterway
Speaker 1: is a northern branch of the cook Inlet that cuts
Speaker 1: into the Greater Anchorage area. Here, the water normally flows
Speaker 1: out toward the inlet, but shortly after low tide waves
Speaker 1: move in the opposite direction and travel upstream, and these
Speaker 1: waves can be epic in scale. The biggest waves are
Speaker 1: up to ten ft or three meters tall. This is
Speaker 1: a well known example Boar tides also known as tidal
Speaker 1: bores or just boars, and riding them has become a
Speaker 1: rite of passage for many surfers in the Pacific Northwest.
Speaker 1: While this phenomenon has been seen at numerous locales around
Speaker 1: the world, it requires a very specific set of conditions.
Speaker 1: But before we dive into those, it might be a
Speaker 1: good idea to go over some basic tidal science. By
Speaker 1: and large, tides are gravity's handiwork. Due to the gravitational
Speaker 1: influence of our moon plus the inertia of our movement
Speaker 1: through space, the ocean is always bulging out a bit
Speaker 1: on opposite sides of the planet. While Earth rotates, it
Speaker 1: passes through these tidal bulges. That means your favorite seaside
Speaker 1: beach will experience high tide when it enters each bulge,
Speaker 1: and low tide as it travels between them, So plan
Speaker 1: your sandcastle contests accordingly. Because Earth finishes a new rotation
Speaker 1: around its axis once every twenty four hours, most coastal
Speaker 1: areas witness two high tides and two low tides per day,
Speaker 1: but there are loads of exceptions. The layout of continents, islands,
Speaker 1: and peninsulas impedes tides in certain places. Parts of the
Speaker 1: Gulf Coast, for example, only see one daily set of
Speaker 1: high and low tides. No matter where you are, though,
Speaker 1: the tides will vary in strength from day to day
Speaker 1: all over the world. During full moons and new moons,
Speaker 1: when the Earth, moon and Sun are arranged in a
Speaker 1: straight line, high tides are especially high and low tides
Speaker 1: are really low. We call these extreme tides spring tides, which,
Speaker 1: despite the name, occur all year round, not just in
Speaker 1: the springtime. But let's turn back to turn Agin Arm.
Speaker 1: Although it's shallow and narrow, the Turnigin feeds into a
Speaker 1: broad bay, namely cook Inlet. On this wide expanse, the
Speaker 1: difference between high and low tides, i e. The tidal
Speaker 1: range can be stark. The cook inlets water level at
Speaker 1: high tide maybe thirty five ft or ten and a
Speaker 1: half meters higher than it was during the preceding low tide,
Speaker 1: and these are exactly the ingredients needed to produce tidal bores.
Speaker 1: After a low tide on cook Inlet, water funnels into
Speaker 1: the herning In Arm, generating boar waves that barrel inland,
Speaker 1: sometimes traveling at speeds up to twenty four miles per hour.
Speaker 1: That's nearly thirty nine kilometers per hour. Since bores only
Speaker 1: happen when the circumstances are just right, not all waterways
Speaker 1: that touch the Ocean can get them. In total, there
Speaker 1: are eighty or so rivers around the globe that undergo
Speaker 1: tidal bores. The phenomenon tends to be at its most
Speaker 1: dramatic during spring tides, whereas the turning in Arm has
Speaker 1: twice daily bore tides. The Amazon River only receives bores
Speaker 1: on the days of new and full moons. Once the
Speaker 1: spring tides arrive, water from the Atlantic comes charging up
Speaker 1: the Amazon River, temporarily reversing its natural flow. Waves generated
Speaker 1: by this process have been known to journey about five
Speaker 1: hundred miles or eight hundred kilometers inland, called porta rocca.
Speaker 1: The Amazon bars attain considerable size, measuring upwards of thirteen
Speaker 1: feet or four meters tall in some cases. The strongest
Speaker 1: portor roca events of all take place every year on
Speaker 1: the equinoxes. To prepare for these surges, local residents move
Speaker 1: their boats and livestock safely away from the Amazon. Accidents
Speaker 1: do still happen, though Jacques Cousteau once lost a boat
Speaker 1: to pororoca waves while filming in South America. Title boars
Speaker 1: impact ecosystems wherever they occur. Trees, rocks, and river bottom
Speaker 1: sediment get pushed around by the waves, and those aren't
Speaker 1: the only things they churn up. Down in the Amazon,
Speaker 1: current reversals can leave stunned or dead animals floating in
Speaker 1: the water, attracting hungry piranhas. Strong boars are also prone
Speaker 1: to eject fish from rivers, stranding them on beaches or
Speaker 1: launching them into the air. That's why Alaskan bald eagles,
Speaker 1: Australian sharks, and Malaysian crocodiles like to scavenge in the
Speaker 1: wakes of title boars. Big boars attract humans as well.
Speaker 1: Sal Domingo Stolkapim, a community that borders the Amazon, has
Speaker 1: been hosting the Brazilian National Poroca Surfing Championship since n
Speaker 1: Alaskan wave chasers flocked the turning in arm shortly before
Speaker 1: or after every spring tide when the boars are at
Speaker 1: their largest. Oh and there's one last thing we should
Speaker 1: mention about boar tides. They roar. The waves produce a
Speaker 1: great deal of turbulence, wildsplacing sediment, scraping up shoals, and
Speaker 1: unleashing loads of air bubbles. Add all those sources up
Speaker 1: and you've got a recipe for thunderous low frequency booms
Speaker 1: that can be heard over vast distances. Today's episode was
Speaker 1: written by Mark Bancini and produced by Tyler. Playing brain
Speaker 1: Stuff is a production of I Heart Radio's How Stuff Works.
Speaker 1: For more on this and lots of other swell topics
Speaker 1: you know, visit our home planet, how stuff Works dot com.
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