by Patrick Orenstein '18
Most geological processes happen very, very slowly. Tectonic plates move on the order of inches per year, rivers take tens of millions of years to carve formations like the Grand Canyon, and a molecule of water can take 500 years to circle the globe through a system of deepwater currents known as the Ocean Conveyor Belt. However, occasionally things can happen a lot quicker, as is the case for earthquakes and volcanic eruptions. Both phenomena represent the culmination of long periods of inactivity during which tension is continuously building until it overcomes the material holding it in place.
About 5.33 million years ago the Mediterranean Sea was much dryer than it is today. The water level is thought to have been 1500 meters shallower and the sea was completely cut off from the Atlantic Ocean. The causes of this dry period, known as the Messinian salinity crisis, remain a topic of disagreement among scientists, but evidence of the period itself is everywhere. Evaporites, materials left behind by past water, were found underneath marine carbonate rocks in sediment cores pulled from Mediterranean seabed in the 1970s, implying a temporary dry period ended by an influx of seawater.
This influx is believed to have come in the form of the Zanclean flood, a sudden deluge from the Atlantic through what is today the Strait of Gibraltar. This flood filled the entire sea to its current level in a matter of years (very fast to a geologist!) and generated water flows thousands of times greater than the Amazon River. In fact, multiple flooding events may have combined to generate the current topographic profile of the Mediterranean, according to an analysis performed by a team at the Institute of Marine Sciences in Barcelona, Spain.
A similar flood was thought to have occurred when the Mediterranean sea connected with the Black Sea around 7000 years ago, possibly causing as much as 100 square kilometers of water a day to spill into it through the Bosphorus and Dardanelles straits. The idea was first proposed in the 1990s by a team led by geologists William Ryan and Walter Pitman. The “Ryan Hypothesis,” as it is sometimes called, claims that the tremendous sound of the flood and subsequent rise in water level changed the course of human history in the area and gave rise to regional legends of catastrophic floods, perhaps even the Old Testament story of Noah’s flood. The connection to biblical legends quickly attracted media attention, spawning a National Geographic TV special and leading Ryan and Pitman to write a book aimed at general readers explaining their idea.
However, most recent research has largely discredited this theory of an explosive flood into the Black Sea, as the expected sedimentary record of such an event has failed to appear in the intervening period. Current evidence suggests a relatively gentle increase in sea level as well as little discernible changes in the behavior patterns of the surrounding peoples. Even National Geographic reported on the reversal in opinion.
The day the Black and Mediterranean seas met appears to have been a relatively uneventful one. But millions of years earlier the area had been shaped by the massive incoming tide from the west, a flood of ocean water carving out basins and gouges in the seabed which had been dry for hundreds of thousands of years. Still an area of incredible geologic activity, the Mediterranean will surely continue to change—check back in a few million years.