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Rivers Under the Sea

April's Shell London lecture, delivered by Jeffery Peakall (University of Leeds) at the Geological Society on 17 April 2013. The modern sea-floor has an abundance of giant channels that can be thousands of miles long, up to several miles wide, and hundreds of metres deep. These submarine channels are the feeder systems and arteries of submarine fans, the largest sedimentary deposits on Earth. Surprisingly these giant ocean-floor channels are perhaps the most poorly known large-scale (up to thousands of miles long) geomorphic feature on the planet. Certainly the channels on Mars, and even Venus, are far more widely recognised! These channels are fed by fast moving particulate-laden flows that are denser than the surrounding seawater and known as turbidity currents. Initiation of these flows can result in small tsunami, and as they travel downslope they can damage sea-floor infrastructure and communications cables; for example they were responsible for a major internet failure in 2006 in the far east. Such submarine channel flows may also play a key role in the carbon cycle through transport and burial of organic material. In addition, the deposits of ancient submarine channels are of increasing importance as hydrocarbon reservoirs, particularly in the Gulf of Mexico and offshore West Africa. Our early models and understanding of these submarine channels were based around comparison with their terrestrial cousins, rivers, yet recent work has highlighted just how dramatically different submarine channels and rivers really are.