Robotic sensors disguised as boulders, or ‘smart boulders’, have been used to measure the initiation and evolution of huge seafloor avalanches for the first time, revealing some surprising findings that will help inform where best to lay the seafloor cables that keep the internet running.

Published this month in the journal Nature Communications, this research shows that submarine avalanches of rock and sand can travel across the seafloor at almost 30 km/hr (similar to a human sprinter), and are powerful enough to move objects weighing almost one ton for several kilometers. Submarine sediment avalanches regularly damage global networks of seafloor telecommunication cables, but they are notoriously difficult to directly measure due to their powerful nature. This multi-year project is the most ambitious attempt yet to measure these avalanches; a total of 15 events were successfully tracked, some of which traveled for over 50 km into the deep sea.

More than 50 instruments were installed on and above the seabed within Monterey Canyon offshore California, including novel smart boulders designed to travel within the avalanches and measure their speed and movement. One of these smart boulders was also attached to a heavy (800 kg) frame that was carried several kilometers down the canyon within a slurry of sand and rock fragments. The presence of such a dense sediment-rich layer at the base of the avalanche came as a surprise, and it challenges many existing theories about how these flows behave.

Repeated seafloor surveys made by robotic submarines revealed that the zone of seafloor affected by this powerful and dense layer was only limited to a thin central part of the submarine canyon. As flows travelled further to deeper water where the canyon was wider, they were also found to slow down. These new findings provide valuable information to identify safe crossing points across other canyons for new seafloor cables and pipelines. —National Oceanography Centre

To learn more about the study, read the paper at https://www.nature.com/articles/s41467-018-06254-6.