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On the very scenic Fanari coastal road is the famous Katavothres (swallow holes) an extremely rare geological phenomenon . . .

. . . It is not known in any other place on Earth!

The seawater flows inland here to enter sinkholes below sea level never to return again, their depth and magnitude unknown.

On 26th February 1963 Austrian hydro geologists dropped 140kg of uranine, a very intensive green colour, into the Katavothres. The colour arrived at Melissani subterranean lake and the springs at Karavomilos fourteen days later, on 12th March 1963. This experiment proved that the opposite sides of the island were connected by an underground system.

Kefalonia is surrounded by water, so that when the underground cave system becomes full no more seawater at Katavothres should be able to enter the system. This does not happen, as the Sami side forms a spring.

The simplified explanation is that salt water is heavier than fresh water (rain), brackish water (a mixture of fresh and seawater) is lighter than sea water but heavier than fresh water. (See the map below).

The cave system contains salt water at the Argosotoli end and brackish water at the Sami end, so the water level is below sea level at Argostoli and above sea level at Sami. The difference is about one meter on both sides.

When the water level in the system rises, the water level of the spring rises, and brackish water flows into the sea, removing water from the system.

As the water level at Sami cannot rise above the level of the spring, the water level at Argosotoli will also stay below sea level. So all in all a third element is needed in the system, the source of the fresh water, which are the rains falling on the karstified (limestone) centre of the island.

As long as rain is fed into the cave system, the different height of water level on both sides remains and water will flow into the Kathavothres, along the cave system into Melissani subterranean lake and out of the springs at Karavomilos.

Water flows from Argostoli to Sami and not vice versa? The reason is the geography: Argostoli is a peninsula, divided from the main island by the harbour of Argostoli. The clay, which covers the sea floor seems to be more or less watertight, as the cave system is not filled with seawater in the area of the harbour. Also no rainwater has a possibility to reach this part of the cave system. This part is always filled with pure salt water, while the rest of the system is filled with brackish water.

In the early 20th century, there was a hydroelectric plant and ice factory, which made use of the force of this water. Unfortunately it is now derelict, with the old waterwheel left to rust, however it is still a very pleasant area to visit especially in the evening . . .

. . . the views overlooking the Gulf of Argostoli are wonderful.

Update: On my return visit to Katavothres in 2010, I was very pleased to find that the whole area including the wheel has been restored. There is a new waterwheel and the sea is still flowing into the sinkholes here.

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