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, after a much slower flow that lasted thousands of years. The water rose very fast at times—maybe more than 10 metres each day.

Researchers believe the water rushed down from a height of over 1,000 metres with an enormous flow, about 100 million cubic metres every second. 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, something special happened. 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 big flood known as 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.

Scientists think the flood might have happened very quickly in geological terms. Some models show that a huge amount of water rushed in, much more than even the biggest rivers today. This 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. Some think there might have been smaller floods before the big one, but the main flood refilled the Mediterranean Sea in just a short time.

Consequences

The Zanclean flood formed the Strait of Gibraltar. It changed the environment of the Mediterranean basin, replacing old land areas with deep sea deposits. The flood may have also affected the global climate.

Rising sea levels turned the deep Nile river into a wide bay, reaching as far as Aswan. The flood isolated islands like Crete, leading to unique plants and animals there. However, 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 evidence of the flood in sediments from that time. The flood likely caused large waves and shifts in the land, influencing the shape of 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 shared a story about Hercules creating the Strait of Gibraltar to connect the Mediterranean Sea with the Atlantic Ocean. The idea about the Zanclean flood started in the 1970s. Scientists discovered salt deposits and erosion in the Mediterranean from a time when the sea level was very low. They found that the sea refilled quickly, in just a few thousand years.