The Mystery of the Tidal Phenomenon of Chalkida, Greece



The bridge of Chalkida at the strait of Evripus

People of Chalkida (or “Halkida”) on the Greek island of Evia have a plenitude 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 tides, which are unique in the world.

The sea currents in the famous Evripus Channel, the 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 eternal process had no beginning and will have no end. 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 from ancient times.

The Evripus Channel as seen by satellite

It has been scientifically proven that these currents, or tides, which occur throughout Earth’s oceans and seas, are created due to the moon’s gravitational pull on the Earth.

However, this cosmic rule has its own, unique exceptions. This periodical phenomenon is based on the lunar month.

On the 7th, the 8th and the 9th lunar days, as well as the 22nd, the 23rd and the 24th lunar days, the waters do not change direction every six hours! It’s possible that during these six days, which are called “The days of the mess,” the waters can change direction up to a total of fourteen times, or they can even not change direction at all and stay still for up to eight minutes!

The speed of the current peaks at about 12 kilometers per hour (7.5 mph or 6.5 knots), both going 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.

The mystery and beauty of this phenomenon has understandably captivated Greeks from 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 is from 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.