Mega-pockmarks and linear pockmark trains on the West African continental margin

Seabed pockmarks, the manifestation of the natural process of fluid escape at the seabed, are a widespread feature of the equatorial West African continental margin. Pockmarks occur singly, in small groups, in large random fields and in organized arrays or ‘pockmark trains’. Pockmark trains are associated with areas of steeper seabed gradient and evolve though time to form deep gullies. Pockmark gullies may exceed 1 km in width and extend for 10–20 km down slope, and form through the interaction of slope failure and fluid escape processes. Gullies maintain a rugose internal geometry throughout their development and do not represent sediment transport pathways to the deep basin. The geological processes that form seabed pockmarks and pockmark gullies are active today and these features may represent a hazard to subsea infrastructure.