More underwater rivers!

Last year I wrote about an 'underwater river' of hydrogen sulphide in a cenote in Mexico. To my amazement, this week I've read two more reports about 'underwater rivers' elsewhere in the world. First, one has been found off Australia.

The undersea phenomenon — layers of dense water that creep along the ocean floor at a rate of about a half-mile (1 km) a day — was found to be some 65 feet (20 meters) thick and stretches for more than 60 miles (100 kilometers).

Researchers say it's the first time these rivers have been glimpsed in such warm waters.

"These dense shelf water cascades are common in high-latitude regions as a result of ice formation, but this is the first time these processes have been discovered in sub-tropical regions, and to be present throughout the year," said the University of Western Australia's Chari Pattiaratchi in a statement.

Water evaporation during the region's summers, followed by cooling during the winters, fuels the formation of the rivers, Pattiaratchi said, leading to the gathering of high-density waters in the coastal shallows, which then flow offshore as slow-moving rivers.

There's more at the link.

That story linked to one about an earlier discovery in the Black Sea.

Researchers estimate that this "undersea river" — known as a submarine channel — would be the sixth largest river in the world if it were located on land, based on the amount of water flowing through it.

Submarine channels are similar to land rivers, but they are formed by currents of water of different densities — mixtures of sand, mud and water are denser than sea water and so sink and flow along the bottom of the ocean.

These channels are the main transport pathway for sediments to the deep sea where they form sedimentary deposits. These deposits ultimately hold not only untapped reserves of gas and oil, but they also house important secrets — from clues on past climate change to the ways in which mountains were formed.

Some suspect the submarine channels in the Black Sea were formed around 6,000 years ago when sea levels were approaching their current point. The Mediterranean Sea swelled and breached through into the Black Sea — once an isolated freshwater lake — via the Bosphorus Strait. As the waters surged, they carried a dense, salty fluid, which formed a network of seafloor channels that are almost constantly active, even today. (Some believe this event was the inspiration for Noah's flood.)

. . .

"Our initial findings show that the flow in these channels is quite different to the flow in river channels on land," said project team co-leader Dan Parsons, of the University of Leeds in England. "Specifically as flow moves around a bend it spirals in the opposite direction in the deep sea compared to the spiral to that found in river channels on land. This is important in understanding the sedimentology and layers of sediment deposited by these systems."

Again, more at the link, including a composite image of the river.

I find it absolutely fascinating to think that rivers like this can exist within other bodies of water. I suppose it's a bit like winds, that can blow in different directions at different heights, without mixing with each other; but these 'underwater rivers' are actually denser than the water surrounding them, heavier, so that their waters can't rise and mingle even if they want to.

I'm going to have to learn more about this subject. It's one of nature's quirks that's really caught my imagination. If any readers can suggest additional sources of information, please tell me about them in Comments.

Peter