Photo credit: phys.org
Approximately 5 million years ago, the Atlantic Ocean made its way through the present-day Strait of Gibraltar, unleashing a torrent of water into the largely arid Mediterranean Sea. This swift inflow of oceanic water is believed to have surged down a steep slope, carving out an extensive trough in the process.
At that time, the Mediterranean basin was primarily dry and saline, but the sheer volume of water entering the region led to its rapid refilling—occurring perhaps within a mere few months to a couple of years. This deluge is estimated to have released an amount of water roughly 1,000 times greater than what flows through the Amazon River today.
This hypothesis was introduced in a 2009 study that examined an underwater canyon near the Strait of Gibraltar, positing that this massive flood carved the canyon. While some scientists contest this theory as detailed in other studies, if validated, the event known as the Zanclean megaflood would mark the most substantial flood event ever recorded on Earth.
As our ongoing research delves into sedimentary rocks from the Zanclean epoch, it appears to provide evidence of how water poured through a channel separating present-day Sicily from mainland Africa, leading to the resurgence of water in the eastern Mediterranean.
Tracing the Origins of the Megaflood
The narrative surrounding this event traces back to the late 1800s when geologists investigating salt-enriched rock formations in the Mediterranean became aware of unusual occurrences dating back around 5 to 6 million years. This interval, known as the “Messinian,” was characterized by the significant desiccation of the sea, which ultimately became recognized as the Messinian salinity crisis.
In the 1970s, scientists conducted significant drilling beneath the Mediterranean, unearthing sedimentary layers from the Messinian period. They made three key findings. Initially, they discovered a vast layer of salt several kilometers thick beneath the seafloor, indicating a significant environmental transformation coinciding with tectonic upheavals that led to the sea’s isolation from the Atlantic.
Additionally, situated above this salt layer was sediment containing fossils from shallow, low-salinity lakes, suggesting that the Mediterranean’s water levels had plummeted significantly, leaving behind salt deposits as water evaporated. The remaining lakes in the basin would have been replenished by streams during this period of aridity, a view corroborated by seismic surveys revealing previously flowing rivers in a now-dry expanse.
Lastly, they observed a transition to distinct deep-sea sediment layers above the salt, with less than 11% of marine species in the Mediterranean surviving the ensuing crisis, illustrating the dramatic and long-lasting effects of this event on marine life. The term Zanclean Flood emerged in the 1970s to describe the recovery phase following the crisis, although the specifics and timeline of the Mediterranean’s refilling remained unclear.
A Dramatic Restoration
A pivotal advancement in understanding this event took place in 2009 when geophysical analyses associated with a proposed Africa-Europe tunnel suggested that a large underwater trench between the Atlantic and the Mediterranean was likely formed by a rapid and catastrophic flood.
In our latest research, conducted under the guidance of Maltese seabed expert Aaron Micallef, we investigated the area where floodwaters should have traversed towards the Sicily Sill, a ridge that connects modern Africa and Italy. This raised the question of whether a second megaflood occurred as the eastern Mediterranean began to refill.
Connecting the Dots
Co-author Giovanni Barreca has lived in southern Sicily and recognized that the coastal low hills are part of the Sicily Sill, potentially holding significant clues about the historical flood.
During our fieldwork in this Sicilian region, we noted the hills’ unusual formations—aligned and streamlined structures divided by deeply worn depressions—remarkably akin to the streamlined hills shaped by the megaflood in Washington State that occurred after the last ice age, when Lake Missoula burst through a glacial dam.
If similar flooding influenced the Sicilian landscape, we hypothesized that rock debris washed away from the erosive depressions would still be evident on the hills today. Our investigation confirmed this, with mixed and displaced rock fragments found atop the hills, closely matching those in the surrounding depressions.
To support our findings, we conducted a computational model simulating the flow of floodwaters across the Sicily Sill. Our simulations indicated that these flows would align with the direction of the hills, revealing that the landforms were shaped by water depths of over 40 meters, moving at speeds reaching 115 kilometers per hour (71 mph). The model predicted water volumes reaching approximately 13 million cubic meters per second entering the eastern Mediterranean, considerably overshadowing the current Amazon’s flow rate of around 200,000 cubic meters per second.
This analysis ultimately illustrates that while this volume represents only a fraction of the initial flow through Gibraltar, it signifies the enormous scale of water movement involved in reshaping the Mediterranean landscape.
Source
phys.org