People of Chalkida (or “Halkida”) on the Greek island of Evia have plenty of reasons to be proud of their historic and beautiful city, but if there’s one thing that stands out among all its other qualities, it would have to be its tidal currents, which are most unique.
The sea currents in the famous Evripus Channel, the extremely narrow strait of water separating Chalkida from the mainland of Greece, move in a northerly direction for six hours at a time.
Immediately afterward follows a period of approximately eight minutes when the waters remain stationary, similar to a “neap tide” which is part of the normal tidal cycle in the world’s oceans.
After the complete stillness of those eight minutes, the waters change their orientation again, reversing direction, flowing toward the south for another six hours.
This process is seemingly eternal. It happens four times each and every day (for the most part—more on that later) and has provoked the admiration and interest of humans since ancient times.
The mystery behind the Phenomenon of Chalkida
It has been scientifically proven that these currents, or tides, which occur throughout Earth’s oceans and seas, are created by the moon’s gravitational pull on the Earth.
However, this cosmic rule has its own, unique exceptions, and that’s what makes this interesting. This periodical phenomenon is based on the lunar month.
On the 7th to 9th and 22nd to 24th lunar days, the waters do not reverse direction every six hours.
It’s possible during these four days, which are called “The days of the mess,” for the waters to either change direction up to a total of fourteen times or not change direction at all but remain still for up to eight minutes instead.
The speed of the current peaks at about 12 kilometers per hour (7.5 mph or 6.5 knots), going both northward and southward, and smaller vessels are often incapable of sailing against it.
When nearing the time of the reversal of the flow, sailing is even more precarious because of the formation of whirlpools.
Studied by Aristotle himself
The mystery and beauty of this phenomenon has understandably captivated Greeks since ancient times. It is said that that the channel took its name from a man called Euripus, who drowned in his valiant attempt to try to solve the mystery of the “crazy waters.”
The great Greek philosopher Aristotle himself, who had ancestors from Chalkida, traveled to the area to study this phenomenon, and a number of other scientists and philosophers have tried to solve the riddle of these irregular tides over the centuries.
In his work Phaedo, Plato has Socrates use the Euripus tide as a simile for things that “go up and down” in describing the thinking of those who hold that nothing is sound or stable. In modern-day Chalkida, visitors continue to be stunned as they observe the change of the water’s direction every six hours (and are perhaps even more perplexed when they view the many changes that can take place during the “Days of the mess”).
The best viewpoint to observe this unique phenomenon from is the old drawbridge in the middle of the city, which is moved to allow for shipping traffic. The bridge is located at the very narrowest point of the strait, where the waters are only 38 meters (125 feet) wide.