Chasing the Tidal Bore
In September my cousin and I drove from New York to Nova Scotia to see our grandparents, who spend the summers there. It had been nearly six months since I’d left the city, and even as we drove up the Hudson Valley and through the Berkshires I could feel the knots in my back start to unwind: a mere river or hill, the simple fact of a lake, seemed novel and marvelous. On the second day of driving we followed the northern Appalachians through New Brunswick until they emptied at last onto the Maritime Plain. The fields—a field, what could be plainer than that?—spread out in all directions like dusty rugs newly unrolled.
I never paid much attention in high school biology, or chemistry, or physics, or in the mandated courses on ecology that I had to take in college. This year, though, I’ve started to fact-check for a science magazine, which has entailed re-acquainting myself with all the specifics of anatomy and astronomy that I mostly ignored ten years ago. At least once a day I google something like “what is photosynthesis” or “water cycle diagram” and curse myself for having spent most of AP Biology fantasizing about playing World of Warcraft when I got home.
Fact-checking has brought science to life for me in a way nothing else ever has, maybe because this time I actually understand the processes that animate the natural world, the laws and tendencies that make our environment seem by turns so temperamental and so sagacious. Thawing ice in the Arctic releases the methane stored in animal carcasses; the modern apple was born when Silk Road traders dropped Kazakh crabapples while meandering through Europe; it would take nearly two billion years for a spacecraft to fly to the other side of the Milky Way.
But to understand a phenomenon, of course, is also to drain it of some of its mystery: once we understand the big, prosaic forces that caused a natural occurrence, it becomes confined in some measure to the realm of the “normal.” In a widely anthologized excerpt called “Two Ways of Seeing a River,” Mark Twain describes how working as a riverboat captain required him to memorize the whole length of his beloved Mississippi. When he had “mastered the language of this water and had come to know every trifling feature that bordered” the path of the steamboat, he says, “all the grace, the beauty, the poetry had gone out of the majestic river.” All the years he had spent as a boy gazing upon its banks were reduced to “the amount of usefulness they could furnish toward the safe compassing of a steamboat.”
Driving into Nova Scotia for the first time, I felt as Twain says he felt when he first saw the sun set over an unfamiliar stretch of the Mississippi: “I stood like one bewitched…the world was new to me and I had never seen anything like this at home.” The peninsula feels less like another country than another continent or planet: it is a place of extreme, alien beauty, its landscape carved and deformed in miraculous ways by unfamiliar forces.
The peninsula’s greatest wonders are on the western shore, where the Bay of Fundy sits between Maine and Nova Scotia. As I learned while fact-checking earlier this year, water in any large container tends to slosh back and forth through a process called basin-mode oscillation. (You know this if you’ve ever sat still in a bath and watched the water seesaw around you.) But because the Bay of Fundy is enormous, extremely deep, and shaped something like a funnel, the sloshing takes an unusually long time, about twelve hours. That period happens to coincide with the length of a typical tidal cycle as dictated by the orbit of the moon. As a result when the flood tide moves toward the shore, the whole basin sloshes toward the shore in unison with it, and vice versa. It’s as if the tides got double-bounced on a trampoline: they rise and recede higher and farther on the Bay of Fundy than anywhere else in the world.
On paper this is interesting, sure, but in person it’s stupefying. The receding tide exposes huge stretches of what used to be seafloor, leaving miles of Martian-looking mud in its wake. Boats that bobbed on the docks are left sitting in the sand, and what had been the secrets of the deep — submarine rock formations, huge drifts of seaweed, scuttling crabs — lie open for examination. In steeper places, where the tide recedes from seaside cliffs, the water level can fall more than fifty feet, creating spontaneous caverns and sandbars: rocky islands become stone towers resembling moai, and piers floating just above the surface become bridges perched high above the ground.
Millions of people visit the Bay of Fundy every year to see the natural formations created by these tides. They come, and I came, because they want to see something beautiful and unfamiliar, but also because they want to see nature looking somehow “unnatural,” see the world looking like it’s not “supposed to” look. We know there is an explanation, because there is one of those for everything, but what attracts us is the sense that we are witnessing something that cannot be explained.
When it returns, the incoming tide swallows up to three miles of land over the course of six hours, the water’s edge advancing at a rate of around forty feet per minute. You can step onto a rock formation, stand there for twenty minutes, and step down into waist-deep water. As the tide moves further up the funnel of the bay, it gets squeezed into moving even faster, flowing inland with greater force. And in just a few places along the bay, the tide pours past the coastline and into a low-lying river, gathering even more force until it becomes a wide, scythelike wave. This wave lands so hard at the mouth of the river that it changes the river’s direction, pushing all the outflowing water back up the riverbank, making it twist and buckle in eddies and frothing whorls.
This wave is called a tidal bore, and the Bay of Fundy is one of the only places in the world where you can witness it. And witness it people do: they pull off the highway into nondescript towns along the head of the bay and drive out to the banks of stagnant, weed-carpeted rivers. Some of them unfold blankets, others munch on chips, still others adjust their binoculars. They wait, mostly in silence, for the arrival of the bore.
Tidal bores have been a tourist attraction for at least three thousand years; the largest bore, and the earliest-discovered, is located near the Huangzhou Bay in China. (Marco Polo missed it when he passed through.) The word “bore” comes probably from the Icelandic “bara,” meaning billow or wave, making these phenomena the only real “tidal waves.” There are other, more mythical names as well: the French, describing the bore that occurs near the mouth of the Seine in Gascony, called it “mascaret,” which means “galloping ox”; the bore on the Amazon is called “pororoca,” perhaps meaning “great roar”; an archaic name for the bore on the Trent River in England is the “eagre,” which most likely comes from the Latin “augurum,” meaning “divine omen.”
This last name is probably the most appropriate. On video, a tidal bore might look like little more than a particularly feisty strip of foam; in person, though, when you’ve been sitting for half an hour watching the river trundle toward the sea, a hissing, slithering wave coming in the opposite direction feels like a sign from God, a direct indication of the sentience of the natural world. Birds sitting on the riverbanks scatter in all directions. The water caves in behind the crest of the wave, turns brown or white seemingly at random. Even after the bore has deported, huge ripples beat on against the current, tossing themselves against the banks and bringing chunks of rock and dirt down with them. One watches and thinks to oneself, didn’t this happen at some point in the Bible? The Book of Exodus, maybe? Nothing could be more “natural” than the phenomenon before our eyes, and yet it is magic precisely because it seems so unnatural, seems like a violation of the rules rather than an expression of them.
For as long as people have witnessed these bores, they have studied them, tracking their size and the frequency of their incidence. As with so many natural phenomena, they were terrifying at first: a tidal bore on the Indus River is supposed to have wiped out the fleet of Alexander the Great around 325 BC, and as late as the 1800s the mascaret on the Seine was still causing hundreds of boats to disappear. Meanwhile, in China, engineers dug out bore shelters along the Huangzhou for junks that encountered the wave while trying to make it to port.
In time, though, the mystery of their origin became clear, and now a litany of studies can reveal how the compression of a channel and the inertia of the water out at sea can affect the size of a bore, as well as explain the individual surges in the bore itself and the way the arrival of a bore messes up the particulate matter on the riverbed beneath. And as we’ve started to understand the bores, we’ve also started to tame them: the excessive ranching of Asian water buffalos has been blamed for the disappearance of the Amazon bore, while in New Brunswick, the construction of a causeway significantly weakened the strength of the bore on the Petticodiac River until 2010, when the causeway’s gates were opened permanently. When the bore regained its strength, it dredged up the remnants of ships from the 1800s and deposited them along the river.
Marco Polo, had he caught sight of a tidal bore in Huangzhou, might have been forgiven for thinking it represented a divine omen, the belligerent impulse of some angry god; today, however, we have no such excuse. Centuries of oceanography, limnography, cymatics, and who knows what else have all but decoded the tidal bore and all the anomalies like it. One wonders, though: did we gain something with all that knowledge, or lose something? And do we flock to the tidal bore today because, at least until we get back in the car and open up a program called “Safari” on our phones, it doesn’t seem like something we can just Google an explanation for?
Twain lost sight of the river when he got to know it too well, but maybe that curse doesn’t have to befall anyone who wants to know what makes the world around her move. In his beautiful eulogy for Henry David Thoreau, Ralph Waldo Emerson described how his friend “knew the country like a fox or a bird, and passed through it as freely by paths of his own,” how “he knew every track in the snow or on the ground, and what creature had taken this path before him,” and traveled with a book to record his sightings. Thoreau, Emerson says matter-of-factly, was “equally interested in every natural fact.” He wanted to know everything he could about the world and how it worked, yet he never lost his capacity for wonderment. Sometimes knowing how an animal evolved or how a landscape was formed only makes its strangeness and its beauty more apparent.
Emerson recalls how, while they were out walking in the woods one day, Thoreau came close to spotting a night-warbler, a bird he’d wanted to see for more than a decade.
He heard a note which he called that of the night-warbler, a bird he had never identified, had been in search of twelve years, which always, when he saw it, was in the act of diving down into a tree or bush, and which it was vain to seek…I told him he must beware of finding and booking it, lest life should have nothing more to show him. He said, “What you seek in vain for, half your life, one day you come full upon, all the family at dinner. You seek it like a dream, and as soon as you find it you become its prey.”
I’m not sure what it would mean to “become prey” to an experience, but I imagine it involves finding all your preparations swept aside, opening the door to your storehouse of facts to find it empty. You stand on the cliff and watch the river change directions, and you know why it’s happening — you know what basin oscillation and tidal resonance are, after all — but you also know that rivers don’t just change directions.
Such moments of wonderment are often far more powerful than the mere knowledge we acquire from hours spent bent over books or stumbling around Wikipedia. But if that’s the case, why do we bother learning anything at all — why did Thoreau carry that book around if all he wanted was to become prey to the night-warbler? Perhaps we keep shoveling facts into the storehouse because we know it will never be enough, that the world will always outstrip our efforts to understand it. Perhaps we like the feeling we get when the natural world flits just out of our reach, confounding our expectations. There’s an explanation for everything, of course, and yet the devious beauty of the natural world is that even when we have found out all of its secrets it insists on turning out to be a little stranger than we had imagined.
It’s one thing to know what a tidal bore is, and it’s another thing to see a tidal bore, but what enchants us about nature is neither the one nor the other but the tension and the torsion between the two. We know how the water has come roaring back up the river, but we don’t know why. We love learning because it feels like each new fact gets us closer to the bigger answer, but also because we know, at some deeper level, that it will never get us all the way there. We can study the river as much as we want, memorize its every bend and cranny, but we can never say for sure that a filthy, foam-flecked wave won’t come rushing at us from the opposite direction, just when we think we know everything.