The geological story of southern Spain
Chapter 3
the Messinian salinity crisis
The Mediterranean is almost like a giant lake, very nearly closed off at the Straits of Gibraltar; and around 6 million years ago, as the advancing mountain arc passed through the site of present day Gibraltar, the Mediterranean, was indeed closed off - an event called the Messinian salinity crisis.
Deprived of fresh influx from the Atlantic, the waters evaporated; sea-level fell an estimated 1300-1500m; and the entire Mediterranean dried out within 2000 years leaving only a few hyper saline, Dead Sea-like, pockets. Just as would happen if you evaporated a dish of salt water, enormous volumes of salt were deposited as the sea dried up (along with dry sands blown in from the surrounding land) - see section on Sedimentary rocks. There are actually salt mines under Sicily that have mined this salt for about 50 years now - and the remaining reserves of salt are reckoned to be about 1 million years worth ! Cycles of partly or nearly complete desiccation continued from 6 to just over 5 my when the Straits finally re-flooded in an event called the Zanclean Flood (5.33 my). The rate of evaporation from the Med today is three times the influx from surrounding rivers and lakes – and it relies on daily currents from the Atlantic to keep it topped up. If the Straits closed again, which they could, it is estimated that the Med would dry out within 1000 years. [Next: Chapter 4 - latest moulding] |