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Turbidity currents: The mysterious underwater avalanches reshaping Earth

Turbidity currents are cascades of sediment that tumble down Earth’s 9000 submarine canyons carrying carbon, plastics and pharmaceuticals into the deep sea. We are finally learning just how often these dramatic events occur.


24 January 2023

New Scientist Default Image

Pete Reynolds

IN NOVEMBER 1929, a huge earthquake in the Grand Banks off the south coast of Newfoundland in Canada sent tremors as far as New York. As the sea floor shook, a vast quantity of sand and mud began to stir up and flow down a canyon, gathering momentum as it went, creating a dramatic underwater avalanche. It involved enough material to make two Mount Everests and triggered a tsunami that killed more than 25 people.

This is the biggest known example of an undersea avalanche, but it wasn’t a one-off. Beneath the waves, the largest avalanches in the world regularly occur in Earth’s coasts and oceans, carving out the deepest and longest canyons on our planet. Most of the time, they happen without anyone noticing.

For hundreds of years, the only witnesses to these events were fish and deep-sea creatures, which might have been carried out to sea or fed by the nutrient-rich sediments that the currents carry with them. More recently, ruptured gas pipelines and broken communication cables were proof that something extreme was going on. Over the past few years, however, things have started to change.

Now, thanks to a series of experiments and a bit of luck, we have captured these Earth-carving events in action. It turns out the mazes of underwater canyons, many of which were long thought to be geologically inactive, are anything but. Armed with new data, researchers have begun to piece together a better picture of what submarine avalanches are like, how they shape Earth and their vital role in locking away the carbon warming our world.

The deepest and longest canyon systems …

Source link The mysterious phenomenon of turbidity currents has, for centuries, reshaped the seabed, creating underwater canyons and plains. A turbidity current is a fast, underwater avalanche of sediment and water. They are the largest sediment transport system on Earth and can travel thousands of kilometers through the ocean, often reaching depths of 1,000 meters or more.

Turbidity currents occur when a river becomes so muddy or sediment-filled that its flow becomes unstable. This causes turbulence in the river, forming a dense undercurrent of sediment and water that flows quickly downriver. As the sediment and water traverse downstream, they begin to form submerged ridges and trenches on the seabed, creating deep underwater canyons, trenches, and plains.

Turbidity currents are powerful enough to move large masses of sediment and rock, creating underwater relief features that can span hundreds of kilometers. For example, the Amazon Canyon, located off the coast of Brazil, is one of the largest undersea landforms on Earth. It is nearly 600 kilometers long and plunges to a depth of over 8,000 meters.

In addition to forming prominent undersea landforms, turbidity currents also pose a risk to seafarers, as they can produce exceptionally strong and powerful currents. Ships traveling in affected areas may experience extreme turbulence and loss of control. It is important for seafarers to be aware of turbidity currents and to avoid voyage routes where they may be encountered.

Turbidity currents are an important natural process that helps to shape and form the seabed, but they also carry ample risks for seafarers. By understanding this phenomenon and its effects, perhaps we can gain a greater appreciation of the power of nature and the unique role it plays in Earth’s ecosystem.

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