https://www.sciencedaily.com/releases/2018/07/180705113954.htm

The 1929 Grand Banks underwater avalanche, which was triggered by an earthquake off the coast of Newfoundland, is the first and only underwater avalanche of this size to have been directly measured.

Despite being extremely common, little is known about underwater avalanches as they are exceptionally difficult to measure; inaccessible and destructive. However, they pose a major geohazard to seafloor infrastructure, such as telecommunication cables that carry more than 95% of global internet traffic, and oil and gas pipelines.