1 00:00:01,920 --> 00:00:06,560 Speaker 1: Welcome to brain Stuff production of I Heart Radio, Hey 2 00:00:06,600 --> 00:00:10,400 Speaker 1: brain Stuff, Lauren vocal bomb. Here. The Alaskan coast is 3 00:00:10,400 --> 00:00:13,000 Speaker 1: as dramatic as it is vast, and it spans over 4 00:00:13,039 --> 00:00:16,400 Speaker 1: thirty three thousand miles or over fifty four thoud kilometers. 5 00:00:17,920 --> 00:00:21,200 Speaker 1: U s State owes its very name to this sweeping ocean. Border. 6 00:00:21,680 --> 00:00:24,959 Speaker 1: Alaska is an English language corruption of an Alouette term that, 7 00:00:25,079 --> 00:00:28,240 Speaker 1: according to one translation, means the shore where the sea 8 00:00:28,320 --> 00:00:31,200 Speaker 1: breaks its back. And if you drive out to a 9 00:00:31,240 --> 00:00:33,360 Speaker 1: place called turning in Arm in the Gulf of Alaska 10 00:00:33,440 --> 00:00:35,479 Speaker 1: at just the right time, you get to watch some 11 00:00:35,520 --> 00:00:40,280 Speaker 1: aquatic action that's pretty spectacular. The turnig In Arm Waterway 12 00:00:40,400 --> 00:00:42,320 Speaker 1: is a northern branch of the cook Inlet that cuts 13 00:00:42,320 --> 00:00:45,839 Speaker 1: into the Greater Anchorage area. Here, the water normally flows 14 00:00:45,880 --> 00:00:49,440 Speaker 1: out toward the inlet, but shortly after low tide waves 15 00:00:49,479 --> 00:00:52,880 Speaker 1: move in the opposite direction and travel upstream, and these 16 00:00:52,880 --> 00:00:55,480 Speaker 1: waves can be epic in scale. The biggest waves are 17 00:00:55,520 --> 00:00:58,840 Speaker 1: up to ten ft or three meters tall. This is 18 00:00:58,840 --> 00:01:02,240 Speaker 1: a well known example Boar tides also known as tidal 19 00:01:02,280 --> 00:01:05,040 Speaker 1: bores or just boars, and riding them has become a 20 00:01:05,120 --> 00:01:07,720 Speaker 1: rite of passage for many surfers in the Pacific Northwest. 21 00:01:09,160 --> 00:01:11,880 Speaker 1: While this phenomenon has been seen at numerous locales around 22 00:01:11,880 --> 00:01:15,039 Speaker 1: the world, it requires a very specific set of conditions. 23 00:01:15,560 --> 00:01:17,760 Speaker 1: But before we dive into those, it might be a 24 00:01:17,760 --> 00:01:21,800 Speaker 1: good idea to go over some basic tidal science. By 25 00:01:21,840 --> 00:01:25,800 Speaker 1: and large, tides are gravity's handiwork. Due to the gravitational 26 00:01:25,800 --> 00:01:28,279 Speaker 1: influence of our moon plus the inertia of our movement 27 00:01:28,280 --> 00:01:31,119 Speaker 1: through space, the ocean is always bulging out a bit 28 00:01:31,160 --> 00:01:34,880 Speaker 1: on opposite sides of the planet. While Earth rotates, it 29 00:01:34,920 --> 00:01:38,880 Speaker 1: passes through these tidal bulges. That means your favorite seaside 30 00:01:38,880 --> 00:01:41,560 Speaker 1: beach will experience high tide when it enters each bulge, 31 00:01:41,760 --> 00:01:44,360 Speaker 1: and low tide as it travels between them, So plan 32 00:01:44,440 --> 00:01:49,240 Speaker 1: your sandcastle contests accordingly. Because Earth finishes a new rotation 33 00:01:49,280 --> 00:01:52,760 Speaker 1: around its axis once every twenty four hours, most coastal 34 00:01:52,800 --> 00:01:56,400 Speaker 1: areas witness two high tides and two low tides per day, 35 00:01:56,960 --> 00:02:00,640 Speaker 1: but there are loads of exceptions. The layout of continents, islands, 36 00:02:00,640 --> 00:02:04,240 Speaker 1: and peninsulas impedes tides in certain places. Parts of the 37 00:02:04,240 --> 00:02:07,280 Speaker 1: Gulf Coast, for example, only see one daily set of 38 00:02:07,360 --> 00:02:11,480 Speaker 1: high and low tides. No matter where you are, though, 39 00:02:11,680 --> 00:02:14,120 Speaker 1: the tides will vary in strength from day to day 40 00:02:14,280 --> 00:02:16,880 Speaker 1: all over the world. During full moons and new moons, 41 00:02:17,080 --> 00:02:19,120 Speaker 1: when the Earth, moon and Sun are arranged in a 42 00:02:19,160 --> 00:02:22,680 Speaker 1: straight line, high tides are especially high and low tides 43 00:02:22,680 --> 00:02:26,840 Speaker 1: are really low. We call these extreme tides spring tides, which, 44 00:02:26,919 --> 00:02:29,360 Speaker 1: despite the name, occur all year round, not just in 45 00:02:29,400 --> 00:02:33,639 Speaker 1: the springtime. But let's turn back to turn Agin Arm. 46 00:02:33,680 --> 00:02:36,560 Speaker 1: Although it's shallow and narrow, the Turnigin feeds into a 47 00:02:36,600 --> 00:02:40,640 Speaker 1: broad bay, namely cook Inlet. On this wide expanse, the 48 00:02:40,639 --> 00:02:43,400 Speaker 1: difference between high and low tides, i e. The tidal 49 00:02:43,520 --> 00:02:46,920 Speaker 1: range can be stark. The cook inlets water level at 50 00:02:46,960 --> 00:02:49,160 Speaker 1: high tide maybe thirty five ft or ten and a 51 00:02:49,200 --> 00:02:52,280 Speaker 1: half meters higher than it was during the preceding low tide, 52 00:02:53,560 --> 00:02:56,720 Speaker 1: and these are exactly the ingredients needed to produce tidal bores. 53 00:02:57,320 --> 00:02:59,880 Speaker 1: After a low tide on cook Inlet, water funnels into 54 00:02:59,880 --> 00:03:03,280 Speaker 1: the herning In Arm, generating boar waves that barrel inland, 55 00:03:03,600 --> 00:03:06,120 Speaker 1: sometimes traveling at speeds up to twenty four miles per hour. 56 00:03:06,240 --> 00:03:10,560 Speaker 1: That's nearly thirty nine kilometers per hour. Since bores only 57 00:03:10,600 --> 00:03:13,560 Speaker 1: happen when the circumstances are just right, not all waterways 58 00:03:13,560 --> 00:03:16,280 Speaker 1: that touch the Ocean can get them. In total, there 59 00:03:16,320 --> 00:03:18,520 Speaker 1: are eighty or so rivers around the globe that undergo 60 00:03:18,600 --> 00:03:21,240 Speaker 1: tidal bores. The phenomenon tends to be at its most 61 00:03:21,280 --> 00:03:25,960 Speaker 1: dramatic during spring tides, whereas the turning in Arm has 62 00:03:25,960 --> 00:03:29,320 Speaker 1: twice daily bore tides. The Amazon River only receives bores 63 00:03:29,360 --> 00:03:32,359 Speaker 1: on the days of new and full moons. Once the 64 00:03:32,400 --> 00:03:35,680 Speaker 1: spring tides arrive, water from the Atlantic comes charging up 65 00:03:35,680 --> 00:03:40,200 Speaker 1: the Amazon River, temporarily reversing its natural flow. Waves generated 66 00:03:40,200 --> 00:03:42,200 Speaker 1: by this process have been known to journey about five 67 00:03:42,280 --> 00:03:47,080 Speaker 1: hundred miles or eight hundred kilometers inland, called porta rocca. 68 00:03:47,360 --> 00:03:51,080 Speaker 1: The Amazon bars attain considerable size, measuring upwards of thirteen 69 00:03:51,080 --> 00:03:54,160 Speaker 1: feet or four meters tall in some cases. The strongest 70 00:03:54,160 --> 00:03:56,520 Speaker 1: portor roca events of all take place every year on 71 00:03:56,600 --> 00:04:00,800 Speaker 1: the equinoxes. To prepare for these surges, local residents move 72 00:04:00,840 --> 00:04:03,920 Speaker 1: their boats and livestock safely away from the Amazon. Accidents 73 00:04:03,960 --> 00:04:06,560 Speaker 1: do still happen, though Jacques Cousteau once lost a boat 74 00:04:06,600 --> 00:04:11,120 Speaker 1: to pororoca waves while filming in South America. Title boars 75 00:04:11,160 --> 00:04:14,960 Speaker 1: impact ecosystems wherever they occur. Trees, rocks, and river bottom 76 00:04:14,960 --> 00:04:17,600 Speaker 1: sediment get pushed around by the waves, and those aren't 77 00:04:17,600 --> 00:04:20,239 Speaker 1: the only things they churn up. Down in the Amazon, 78 00:04:20,480 --> 00:04:23,400 Speaker 1: current reversals can leave stunned or dead animals floating in 79 00:04:23,440 --> 00:04:27,400 Speaker 1: the water, attracting hungry piranhas. Strong boars are also prone 80 00:04:27,400 --> 00:04:30,080 Speaker 1: to eject fish from rivers, stranding them on beaches or 81 00:04:30,120 --> 00:04:33,039 Speaker 1: launching them into the air. That's why Alaskan bald eagles, 82 00:04:33,120 --> 00:04:36,000 Speaker 1: Australian sharks, and Malaysian crocodiles like to scavenge in the 83 00:04:36,080 --> 00:04:39,960 Speaker 1: wakes of title boars. Big boars attract humans as well. 84 00:04:40,440 --> 00:04:43,680 Speaker 1: Sal Domingo Stolkapim, a community that borders the Amazon, has 85 00:04:43,720 --> 00:04:46,920 Speaker 1: been hosting the Brazilian National Poroca Surfing Championship since n 86 00:04:48,360 --> 00:04:51,279 Speaker 1: Alaskan wave chasers flocked the turning in arm shortly before 87 00:04:51,440 --> 00:04:53,560 Speaker 1: or after every spring tide when the boars are at 88 00:04:53,600 --> 00:04:57,400 Speaker 1: their largest. Oh and there's one last thing we should 89 00:04:57,440 --> 00:05:01,400 Speaker 1: mention about boar tides. They roar. The waves produce a 90 00:05:01,440 --> 00:05:05,080 Speaker 1: great deal of turbulence, wildsplacing sediment, scraping up shoals, and 91 00:05:05,160 --> 00:05:08,279 Speaker 1: unleashing loads of air bubbles. Add all those sources up 92 00:05:08,320 --> 00:05:11,200 Speaker 1: and you've got a recipe for thunderous low frequency booms 93 00:05:11,360 --> 00:05:19,320 Speaker 1: that can be heard over vast distances. Today's episode was 94 00:05:19,360 --> 00:05:22,240 Speaker 1: written by Mark Bancini and produced by Tyler. Playing brain 95 00:05:22,240 --> 00:05:24,400 Speaker 1: Stuff is a production of I Heart Radio's How Stuff Works. 96 00:05:24,640 --> 00:05:26,760 Speaker 1: For more on this and lots of other swell topics 97 00:05:26,960 --> 00:05:29,960 Speaker 1: you know, visit our home planet, how stuff Works dot com. 98 00:05:30,000 --> 00:05:32,040 Speaker 1: And for more podcasts on my heart radio, visit the 99 00:05:32,080 --> 00:05:34,680 Speaker 1: iHeart Radio app, Apple Podcasts, or wherever you listen to 100 00:05:34,720 --> 00:05:35,520 Speaker 1: your favorite shows.