Scientists have unearthed the origins of one of the Middle East’s great rivers, the Euphrates, which is closely tied to the development of civilisation in the region.
Also linked to the biblical Garden of Eden, the Euphrates is West Asia’s largest river, stretching for 1,740 miles through Turkey, Syria and Iraq before emptying into the Arabian Gulf.
The river was in the headlines last week for very different reasons as flooding led to it bursting its banks, with thousands of people affected and evacuation orders issued in Turkey and Syria.
A new study has found that two key tributaries of the Euphrates previously flowed into the eastern Mediterranean before, at different times millions of years ago, they switched direction.
The extraordinary discovery partly came from analysing oil and gas exploration data that highlighted the presence of the rivers’ sediments beneath the eastern Mediterranean seabed.
One of the scientists involved, Prof Richard Walker, of the University of Oxford’s Department of Earth Sciences, told The National that, because of the discovery, being involved in the research had been “an amazing experience”.
“The evidence is there. It’s hidden, but with painstaking work you can piece it together and find something new,” he said. “It’s sometimes rare for us to really make such a big change in our understanding. That’s really, really exciting.”
Mysterious river
Despite the Euphrates’ significance, its history had been shrouded in mystery, with the researchers saying in their Nature Geoscience study that when it formed and where it flowed “remained enigmatic”.
About 5.5 million years ago the narrowing of the Mediterranean Sea’s connection to the Atlantic Ocean resulted in a drop in sea level that caused kilometre-thick salt deposits to form on the sea floor through evaporation.
Reconstructing millions of years into the past
Above these salt deposits – which exist far below the present-day seabed – researchers identified deposits from the ancient equivalents of the Murat and Karasu rivers, the Euphrates’ two main tributaries.
These two ancient rivers, which they named the Palaeo-Murat and Palaeo-Karasu, would have delivered vast amounts of water and sediment into the Mediterranean basin.
“You wouldn’t assume that these river systems used to go to the Mediterranean at all,” Prof Walker said. “One of the big breakthroughs that happened not that many years ago was showing these huge amounts of gravel – river gravel – are present beneath the seabed of the Eastern Mediterranean.”
Techniques including seismic reflection profiling, in which reflected sound waves indicate what lies beneath the surface, helped identify the presence of the deposits.
Digging deep
Seismic reflection profiling is heavily used in the oil and gas industry and several of the authors of the new study are employed by the American energy company Chevron.
Another of the paper’s authors, Dr Claudia Bertoni, also of the University of Oxford’s Department of Earth Sciences, said the improved availability of crucial data had been key to the research.
“The data was not available until recently,” she told The National. “The information off the coast was basically coming from previously inaccessible data, from the exploration industry, which is usually confidential. And the quality of land data has massively improved in the last few years, with satellite images.”
From the Eastern Mediterranean deposits, the researchers traced the rivers backwards, although working out their course based on present-day terrain was not straightforward because of changes, such as mountain formation.
According to the research, the Palaeo-Murat River developed some time after 16.55 million years ago, while the Palaeo-Karasu River formed between 8.6 and 5.9 million years ago.
The course of both rivers was changed because of tectonic activity or changes to the Earth’s crust.
About 3.6 million years ago, the Palaeo-Murat switched to flow towards the Arabian Plate, while the Palaeo-Karasu followed suit around 2.8 million years ago.
“Tectonic movements caused this shift and the regional change in land gradients – this is still a tectonically very active area, as shown by the frequent earthquakes,” Dr Bertoni said.
“At the same time the desiccated Mediterranean reflooded again, so the river base level became much higher, so the river sediment could not be discharged any more on the submerged Mediterranean Sea floor.”
Prof Walker said changes of course by rivers over time were not unusual, adding that “sometimes it doesn’t take much” to make this happen.
“They work on very low gradients,” he said. “If there is a blockage, a critical change, if mountains are being uplifted, they form a blockage to the channel flow, it can be easier for the rivers to divert.
“If you have a landslide and it blocks the river, what happens? You form a lake. Maybe it tips over into its original channel, maybe it starts to divert and go into another direction. It’s actually quite a common process through Earth's history for rivers to reorganise.”
About 1.6 million years ago the Murat and the Karasu, having both switched direction away from the Eastern Mediterranean, joined and created the modern Euphrates, which links with the Tigris to form the Shatt Al Arab waterway. This flows into the Arabian Gulf.
The area between the Euphrates and Tigris, part of a wider region known as the Fertile Crescent because of its nutrient-rich soil and water supplies made it ideal for agriculture, was a centre for the origin of civilisation.
Several cities from the Sumer civilisation – believed by many to be the world’s earliest civilisation, located in southern Mesopotamia about 4500 BC – were close to the Euphrates’ southern end, while later on, the city of Babylon was built by the river.
In the Bible, the river is described as one of four flowing from the Garden of Eden, where Adam and Eve are said to have lived.
The researchers, who work at institutions in Australia, the UK and the US, have published their findings in a paper titled, “Late Miocene Euphrates River drained into a partially desiccated eastern Mediterranean.” The lead author is Dr Andrew Madof, a senior scientist with Chevron’s Eastern Mediterranean business unit.
