Island and Coastal Aquifers - Hydrogeology: Objectives, Methods, Applications - page 68

Cavities can exist around the periphery of marine springs, functioning
like estavelles, absorbing seawater or emitting brackish water, depending
on the season. The ones in the Bay of Bali (Crete) absorb approximately
1 m 3 ·s -1 , and have been proven through tracing to be connected to the
coastal springs at Syphona, 6 km away. They may also be connected to
the Almyros spring in Iraklion (elevation 3 to 10 m), located 30 km to the
southwest, but no tracer tests have been able to prove the connection, and
recent studies (Arfi b, 2001) refute this hypothesis. The estavelles of Kola
(Croatia) absorb 100 L·s -1 , and a tracer test has shown a link with the coastal
springs of Jurjurevo.
Aspiration can occur on the coast, and is therefore visible, as in the sea-
mills of Argostoli, which are one of the most surprising karst phenomenons
of the planet. On the western coast of the island of Kefalonia (Greece), in the
bay of Livadi, near the town of Argostoli, several coastal karst cavities absorb
sea water. In the past, the throughfl ow was strong enough to power two
mills, but in 1953, following a strong earthquake, it decreased signifi cantly. A
tracer test in 1963 with 140 kg of fl uorescein indicated a connection, after 16
to 23 days of travel below ground, with the brackish springs of Karavomylos,
located in Sami, 15 km to the northeast, on the eastern coast of the island.
The outfl ow into the losses was 1.7 m 3 ·s -1 and the discharge from the springs
was 10 m 3 ·s -1 . This poorly-understood phenomenon has prompted several
interpretations, including notable ones by Glanz (1965), Maurin and Zoetl
(1965), and Drogue (1989). A hypothesis for the functioning of the springs
is proposed below (see chap. A9-2.4).
2.2 The origin of submarine karst springs
Karst systems experience a delayed reaction to variations in sea level,
which are generally rapid (+120 m in 18,000 years, for an average speed of
6.6 mm per year for the last transgression, with even greater instantaneous
velocities, given the existence of pauses). Drains can form during a period
of low sea level, during glaciations for example. After a transgression, if
the permeability of the limestone near the outlet is low, the emergence
can remain functional below sea level, as long as the fresh water is under
greater pressure than the pressure of the overlying seawater. Such springs
are known to exist at depths of up to 80 m (Anavalos, Greece).
Karsts are polyphase systems and their evolution can extend over
millions of years. During these long periods, coastal karsts adapted
to the marine base level, by hollowing out new drainages, but also by
reactivating older drainages. Indeed, within an unconfi ned karst aquifer, the