Fortunately, the massive tidal flows called tsunamis are rare in Greece, but they can occur if conditions are right... and they have been several times in Greek history as well as in the present day.
What Can Cause a Tsunami in Greece?
Greece combines lots of water, many islands, broken and shallow seafloor, and volcanic activity. Unfortunately, these are ideal conditions for tsunamis. The tragic Indonesian tsunami focused attention on these powerful and often deadly waves. While Greece, in the Mediterranean, was safe from that wave, it inspired renewed efforts on the part of the Greek government to develop a tsunami warning system which is not yet fully deployed.
Tsunami Triggers in Greece
An earthquake in Greece or the surrounding area is not the only possible trigger of tsunamis. Major undersea rock slides can also trigger them, and the unseen slopes of the mountains which we know as islands have many areas which could be prone to collapse. Fortunately, we're talking geologic time here, and incidents are rare. Volcanic activity can also cause potential rock slides underwater.
Any time there is a "slip and slide" situation, where there is a sudden displacement of a large amount of rock underwater, there is a potential for a tsunami.
"Mini-Tsunami" Strikes Greece
A sudden group of 6-foot (2 meters) waves scared beach goers and injured four people at beaches along the Gulf of Corinth in August of 2008. The problem is, there was no earthquake registered in Greece. Scientists are scrambled for an explanation and ended up considering two very different explanations - an undersea rock slide disturbing the deep waters of the Gulf of Corinth, or a big wake from a huge yacht.
The only problem is that a major rock slide should have registered on seismological instruments and a ship that fasts, that close and that big should have been seen by beach goers.
Another "mini-tsunami" hit the Cape coast of South Africa on August 25th; like the Greek tsunami, it also came without registering any warnings on any tsunami prediction system.
Many of the quakes that strike Greece have their epicenters under the sea. While these can shake up surrounding islands, they rarely cause severe damage.
The ancient Greeks attributed earthquakes to the God of the Sea, Poseidon, perhaps because so many of them were centered under the waters.
Tsunamis in Ancient Greece
A number of tsunamis struck Greece in ancient times.
The Eruption of Thira (Santorini) circa 1638 BCE
When the once-round island of Thira, now known as Santorini, erupted and vaporized all but a thin crescent of land, the devastation swept the Mediterranean and was a contributing cause of the collapse of Minoan civilization. Since the tsunami in Indonesia, scientists have been applying their new knowledge to estimate the damage from the Thira tsunami. They've found evidence of debris washing well up into the foothills of Crete in some places, more than a mile inland and hundreds of feet up the side of mountains. The loss of life and damage from the tsunami resulting from the Thira explosion would have been far greater than previously calculated.
The Earthquake of Alexandria 365 CE
This dramatic earthquake sent a tsunami across the Mediterranean, hitting the south coast of Crete, where some debris flows can still be seen at various places on the island. This earthquake also accounts for much of the upsurge of coastal rock, which can be seen in many places along the coast. In other places, large areas slid into the sea, disappearing beneath the waters.
Tsunamis in Greece
After the devastating tsunami which struck the Indian Ocean in 2004, Greece decided to install a tsunami-detection system of its own. At present, it is still untested but is meant to give warning of any potentially large waves approaching the Greek islands. But fortunately, the type of earthquake which caused 2004's devastating Asian tsunami is not common in the region of Greece.
There was a small tsunami on May 15th, 2003, caused by an Algerian earthquake which caused the kind of slip and slide damage underwater described above. The resulting wave was fortunately only about 18 inches high. It hit the southern coast of Crete and the southern coasts of other islands as well.
For more information on tsunamis in Greece in historic times, scroll down George Pararas-Carayannis' colorful page on earthquakes and tsunamis in Kythira and the rest of Greece.