Zanclean flood (5.33 million years ago)

Reading Thomas Halliday’s book Otherlands, chapter 3.

The Atlantic has broken through the Straits of Gibraltar and filled up the west side of the Mediterranean. Now read on.

The Maltese-Sicilian sill is a vast natural dam, a barrier between the two deepest basins in the Mediterranean Sea. Across its wide expanse are now scattered sea-lakes. As seawater begins to spill over the dam, the eastern basin will be filled by the greatest waterfall ever to have graced the Earth. It is 1,500 metres — nearly a mile — high, one and a half times the height of the modern-day Angel Falls in Venezuela. The water pours over the escarpment at speeds of 100 miles per hour, and much of it turns to mist before it even reaches the ground. Unlike the Straits of Gibraltar, where the descent into the western Mediterranean basin is gradual, weir-like, this is a true, sheer drop, where the force of an entire ocean is channelled into a single, 5-kilometre-wide site. Even with this constant deluge raising the eastern Mediterranean by a metre every two and a half hours, it will take over a year before the eastern Mediterranean is filled, until Malta, Gozo and Sicily are finally cut off from Africa and Italy, and Gargano becomes an island once more. (p. 51)

Before this, the Mediterranean is described as:

This is the deepest land in the world. Descending into the abyss, the ever-larger weight of the atmosphere pushes down, as winds fall over the cliffs.

When a pocket of air moves downwards, the air pressure rises. Like the air within a combustion engine, the increase in pressure causes the air mass to shrink and to heat. For every kilometre a wind falls, its temperature increases by about 10°C. This is a cool period in Earth's history, but even so, on a hot day, maximum summer air temperatures 4 kilometres down at the base of the plain could reach a hellish 80°C — some 25°C hotter than the hottest temperature ever recorded in modern times in Death Valley, California.

I love these scenes from natural history.  

Related: 5.5 million years ago the Mediterranean dried out, with sobering lessons for humanity today – new research, Daniel García-Castellanos & Konstantina Agiadi, The Conversation, 29 August 2024.