There are a group of rivers around the world with a unique characteristic. But as remarkable as they may be, in some cases they can cost human lives.
Tidal bores are natural phenomena provoked by the pressure of the ocean’s rising tide intersecting with the mouth of a river. When a watercourse is forced to cope with a rapid rise in sea level (and given that the average height of the river is usually not much higher than that level), it can lead to a big confrontation—one which only increases in violence as the hours pass.
This shocking phenomenon culminates in a complete reversal of the direction of the flow. As this flow is reversed, it forms a powerful and penetrating wave that plows upstream, and when opportunity strikes, it will surge through the arms that feed the main river. If conditions are right, and the river describes just the right shape, a magnificent wave is produced. This wave, known as a tidal bore, can measure between 10 and 16 feet high and move at a speed of more than 20 miles per hour.
But this isn’t merely an isolated incident. In fact, the bores usually come in a series rather than in solitary numbers, and the waves tend to last several hours, increasing or decreasing their intensity along their path. At their final destination several miles from the mouth of the river the bores die out, having gradually dissipated as they near the end of the line.
These liquid performances can be found in several places around the world, with a few examples occurring in North America, such as Cook Inlet, Alaska, and several rivers that connect to Canada’s Bay of Fundy.
These unusual waves often receive special names, depending upon the river in which they occur. In Venezuela, they are called “Macareo” (a name given to the bore phenomenon as recognized by the Royal Spanish Academy). In the Amazon, for hundreds of years the natives have called it “pororoca” which in the local Tupi-Guarani language means “great destructive noise.”
Those who have had the opportunity to witness one of these dramatic watery episodes agree that the pororoca is aptly named. It makes a thunderous sound that causes animals to flee, and creates an uncontrolled jumble of coastal birds that instinctively escape from their perches near the bed of the huge river.
The power of this natural phenomenon can be seen in the way it significantly eats away at the river’s edges, devastating trees, rocks, and virtually anything in its path.
Still, the bores remain an irresistible temptation for dozens of surfers who are drawn to this force like flies to honey—hungry for the chance to ride the longest waves in the world. There are even competitions within an official circle of fans of this extreme sport to show who can ride the pororoca the longest.
Wave-Riding Records
These competitions only happen once a year, during a 3-day window in March when the full moon raises the tide to produce the year’s largest waves. But there are also serious consequences for pororoca riders to consider.While the waves are often smaller than those known to ocean surfers, they are also much more dangerous—piranhas, alligators, poisonous snakes, and uprooted trees are obstacles that ocean surfers don’t have to contend with.
Plus, the Amazon does not have the heavy saline content found in the ocean, so it is much more difficult for these river surfers to stay afloat. But if they can withstand the challenges the river presents, these intrepid bore surfers can ride waves far longer than their ocean-traveling counterparts, who are lucky to get a full minute of wave-riding time.
By contrast, several pororoca daredevils have managed to ride these Amazonian monsters for more than 15 minutes. However, the current record is held by Brazilian Picuruta Salazar, who in 2003 rode a wave for 37 minutes, traveling a distance of nearly 8 miles.
Still, the Amazon pororoca is not the largest of the world’s tidal bores. This honor goes to the Qiantang River in China, which has produced waves nearly 30 feet high traveling 25 miles an hour.
Known to the locals as the “Silver” or “Black Dragon,” these powerful waves have taken many lives over the centuries, but every September, when wave are at their peak, several people come to witness this amazing phenomenon of nature.
Further reading: http://www.tidalbore.info
