The study of 13 modern basin plains ranging in size from the 200-km 2 Navidad Basin up to the giant (>100,000-km 2 ) Hatteras and Sohm Abyssal Plains has revealed that these features owe their existence to large-volume turbidity currents capable of covering the entire basin floor. Such convulsive events flatten out the topographic irregularities formed by the deposition of small flows between the big events. Giant events maintain the flat plain floor. The largest event measured to date in modern basin plains is the Black Shell Turbidite of the Hatteras Abyssal Plain, which is at least 100 km 3 in volume and perhaps double that. In some instances, a single giant flow may arrive on the basin simultaneously from geographically widespread basin entry points, indicating that the initiating mechanism, probably an earthquake, was regional in scope.