Massive underwater avalanches deliver pollutants to deep sea

On 18 November 1929, a magnitude 7.2 earthquake shook the ocean floor off the coast of Newfoundland, Canada. Within minutes transatlantic telephone cables started sequentially snapping, with the furthest cable – 600km from the quake – breaking 13 hours and 17 minutes later.

At the time geologists hypothesised that the cables had been broken by a series of earthquakes, but we now know that the culprit was a massive underwater avalanche, known as a “turbidity current”.

These gravity-driven currents are a key way of transporting sediment to the deep sea with the largest able to carry more sediment than the annual output of all the world’s rivers combined. Their deposits, or “turbidites”, can be hundreds or even thousands of metres thick and were assumed to be dumped in a single event, until a new model, described in Science Advances, showed that in fact it happens in many episodes.

The finding will help geologists better identify ancient turbidite deposits (which sometimes contain gold, or oil and gas), and understand modern-day turbidity currents, which as well as transporting sediment to the oceans’ abyssal plains, can deliver plastic litter and other pollutants to the deep sea.