Somebody get Moses on the phone.
Confirming for the first time in nature what had only been seen in lab experiments before, the team watched and recorded as the brown waters from a recent flashflood rushed towards the sea and instead of mixing with it, continued to hug the bottom and flow under the salty water.
When a river meets the sea, the freshwater generally floats on top of the denser salt water or mixes with it creating the muddy fan of a typical river delta.
Dense with dirt and sand picked up along the previously dry river beds, and flowing down a steep slope, these particular floodwaters took the low ground, creating what is called a hyperpycnal (“over-dense”) plume. Seen from above, the billowing clouds of silt resembled vast thunderstorms viewed from an airplane.
Beverly Goodman, from the University of Haifa, took the time to answer a few of our questions about this striking event.
So how often do these underwater mud shows occur?
We are not yet certain, which is part of the reason that we are studying them.
Because this is a very dry area with little precipitation, floods are not common and floods that actually enter into the sea are quite rare. In recent years it has only occurred during three winters in about 17 years.
What does it feel like to swim through them?
Divers can feel a small current inside the plume, but not enough to really affect their direction or to be dangerous. It looks much more dramatic then it feels, though diving in and around it is a lot fun!
Watch divers navigate the hyperpycnal plume:
How do these flows affect life in the sea?
One of our observations was that in the same area where we observed the flood plume there are ancient fossil coral reefs—but no living coral today.
We now understand that in the modern system coral can’t tolerate this amount of sediment, and therefore don’t grow there. However, because we see the ancient coral reefs, there must have been a time when either these floods didn’t enter in the same area, or they didn’t enter at all—perhaps an even hotter and more arid period of time or the opposite, in which some sort of marsh or mangrove system in the shallows managed to trap sediment and protect corals that lived offshore.
Have you discovered any evidence of particularly colossal events like this in the past?
The last few years have been very exciting for research in the Red Sea.
This study was part of a general effort to better understand all of the processes here, and even compare them to some sediment layers that we believe to be caused by an earthquake and tsunami in the past!
Catching this flood at just the right time gave us a chance to show that the other colossal event was not a flood because it was so different when we compared their properties.
What’s next for your team?
Our hope is to now figure out how to recognize these deposits in the deepest part of the sea and reconstruct climate changes in the past based on frequency of flashfloods, which can tell us a lot about the precipitation patterns in the past.