Zanclean flood

The Zanclean flood, also called the Zanclean deluge, is thought to have filled the Mediterranean Sea about 5.33 million years ago. This big flood ended a time when the sea was mostly dry and connected the Mediterranean to the Atlantic Ocean again. This connection started the Zanclean age, which is the first part of the Pliocene on the geologic time scale.

According to scientists, water from the Atlantic Ocean flowed back into the empty sea through the area now known as the Strait of Gibraltar. Most of this flooding happened very quickly, maybe in just a few months to two years. The water rose very fast at times.

Researchers believe the water rushed down from a height of over 1,000 metres with an enormous flow. This is much bigger than the flow of the Amazon River today. Studies of the sea floor show that the water moved down a gentle slope instead of falling like a huge waterfall.

Background

The Mediterranean Sea was shaped by the movement of large pieces of Earth's crust called plates. These plates include the African Plate, the Arabian Plate, and the Eurasian Plate. Over time, these movements closed up the old Tethys Ocean, turning its western part into the Mediterranean we know today.

During a time called the late Miocene, the Mediterranean got cut off from the Atlantic Ocean. This happened when paths like the Guadalhorce and Rifian corridors closed. Because of this, the Mediterranean began to dry up. This period, called the Messinian Salinity Crisis, left thick layers of salt on the seafloor. Rivers like the Nile and Rhône carved deep valleys during this dry time. The water level in the Mediterranean dropped by many kilometers.

Even before the Zanclean flood, there might have been small connections letting water flow in from the Atlantic. Fish from the Atlantic have been found in old layers of earth from this time. Also, more rain and water running off the land helped lower the salt level in what was left of the sea. This led to special layers of mud and sand called "Lago Mare" sediments being formed. The water levels may have gone up and down, possibly getting water from a place called the Paratethys to the north through certain processes.

Event

The Zanclean flood happened when the Strait of Gibraltar opened. This let water from the Atlantic Ocean flow back into the Mediterranean Sea. Before this, the Mediterranean had become very dry because it was cut off from the Atlantic.

The flood changed the shape of the sea floor and connected the Mediterranean to the Atlantic again.

Timing

The Zanclean flood likely happened around 5.33 million years ago. This event marks the start of a new time period called the Zanclean, which is the earliest part of the Pliocene epoch.

Consequences

The Zanclean flood created the Strait of Gibraltar. It changed the environment of the Mediterranean basin, turning old land into deep sea areas. The flood may have also affected the world's climate.

Rising sea levels made the deep Nile river into a wide bay, reaching as far as Aswan. The flood separated islands like Crete, allowing special plants and animals to develop there. The new Strait of Gibraltar stopped land animals from moving between Africa and Europe. Sea animals from the Atlantic could now enter the Mediterranean.

Scientists have found clues about the flood in old sediments. The flood probably caused big waves and changes to the land, shaping mountains like the Apennine Mountains.

Similar megafloods

Other big floods have happened in Earth's past. One example is the Bonneville flood in North America, when Lake Bonneville overflowed through Red Rock Pass into the Snake River Basin. Another is the Black Sea deluge hypothesis, which suggests that water from the Mediterranean flowed into the Black Sea through the Bosporus.

Research history

In his book Historia Naturalis, Pliny the Elder told a story about Hercules making the Strait of Gibraltar to connect the Mediterranean Sea with the Atlantic Ocean. The idea about the Zanclean flood began in the 1970s. Scientists found salt deposits and erosion in the Mediterranean from a time when the sea level was very low. They learned that the sea filled up again quickly, in just a few thousand years.