Counterintuitive stream.

This is a note of something I know I've mentioned before, clearly labelled so I don't forget it.

From the New Scientist, some years ago:

Perpetual motion


On the Greek island of Cephalonia there is a stream of seawater which runs from the beach, along a watercourse and down a hole in the ground about 100 metres further inland. Until the disastrous 1953 earthquake there was enough power from this stream to drive a water mill. How can this be? It is said that the water, after pouring into the hole, emerges in a cave which must be below sea level, but where does the energy come from? How is it possible to have a place below sea level, very close to the sea, where the hydrostatic pressure is less than that of the sea?
DOUG FENNA , Middlesborough Cumbria

The stream near Argostoli, on the western side of Cephalonia, runs the wrong way across the beach, from the sea to a hole about 100 metres inland down which it disappears. It reappears eventually from underwater springs on the seabed near Sami on the eastern side of the island and, although apparently paradoxical, depends for its driving mechanism on the existence of a massive range of mountains between Argostoli and Sami which rise to more than 1500 metres. These are blessed with substantial rainfall and are composed of limestone sedimentary rocks with bedding planes that incline downwards from west to east.

During the last ice age, when the increase in the polar ice lowered sea levels around the world, the sloping lowest strata of these limestone rocks were above sea level. They became eroded by rainwater which fell on the mountains and percolated down through the limestone until it encountered a less permeable rock layer beneath and then flowed downwards along this layer.

The sloping subterranean channels formed by the erosion of the limestone in this way carried the rainwater off to the east coast, where it emerged in springs which were then on land, above the lowered sea level.

Additionally, rainwater running off the west side of the island drained into a stream located in a valley which is now flooded again and known as the Gulf of Lixouri. This stream also eroded its way into the subterranean channels at their western end by disappearing into swallow holes on the western side of the mountain chain and this water, too, was carried eastward, under the mountains. It also emerged from the springs on the eastern side.

At the end of the last ice age, the sea level rose again as the polar icecaps began to recede. By chance, the level to which it rose was almost exactly that of the higher, westward end of the eroded, subterranean channels, so that the channels became flooded and the springs at their eastern end were submerged by the sea.

However, the downward percolation of rainwater through the mountains, which was not affected by the rise in sea level continues, and is still given an eastward deflection by the slope of the bedding planes. This eastward flow of the rainwater as it enters the flooded lower channels beneath the mountains and then issues from the underwater springs at Sami is sufficient to induce behind it a suction effect which lowers the water level in the westward end of the channels. This means there is always room in the hole that one sees on the beach near Argostoli, for the sea to continue to spill into it (in relatively small quantities) and be carried away eastwards through the channels where it mixes with the rainwater and emerges at the springs.

It was some time after the 1953 earthquake that the connection between the hole at Argostoli and the underwater springs at Sami was definitely established, by geologists using a fluorescent dye or radioactive tracer. That work, and the explanation outlined above, were published in papers for which I cannot provide references although I am sure they will be known at the museum in Argostoli.
John Gaskin , Leatherhead Surrey
Melissani cave
Melissani is situated at Karavomilos Village. Melissani is an underground lake, which receives its water by the stream that disappears underground at Argostoli. The indigo colour of the water and the reflections are spectacular, especially in the middle of the day when the sun’s rays fall vertically. The Melissani cave is explored by boat.

There's a cave nearby, the Drogorati cave which has better acoustics for concerts than most of the botched UK attempts at concert halls..
So, the sea water flows into the hole in the beach, along flooded channels of an ancient, sub-surface mountain range and, after mixing with rainwater running through the same channels, emerges in several springs underneath the ocean with enough force to pull more seawater in behind it and so perpetuate the whole cycle?

So how comes the water goes all in my kettle when I turn on a tap?