Three large mass-transport deposits occur on the upper to middle Amazon Cone. These slump/debris-flow complexes have been mapped from 3.5-kHz echograms and cover approximately 75,000 sq km or about 10% of the cone. The debris flows traveled down slopes with gradients as low as 1:90 to 1:165 (0.3 to 0.6°) for distances up to 300 km. These deposits average 10 to 50 m in thickness and the total amount of sediments displaced may exceed 3,800 cu km.

The upslope parts of these complexes generally consist of hummocky slump or slide deposits which are commonly bounded by scarps of varying relief. Downslope from this zone of removal the deposits consist of thin (< 50 m), acoustically transparent debris flows. The two largest slump/debris-flow complexes parallel either side of the central distributary channel system of the cone. This association may suggest that rapid over-bank deposition of fine sediment leads to oversteepening and eventually triggers massive mass movements down the fan. Cores from these two deposits suggest that the mass movements occurred during the late Wisconsin. In contrast, some cores from the third deposit on the western edge of the cone suggest that at least parts of this mass movement may be Holocene in a e.

The occurrence of such widespread mass movements on the Amazon Cone indicates that mass transport is probably an important sedimentation process on deep-sea fans. However, most studies and models of modern deep-sea fans have minimized or ignored the potential importance of mass-transport processes in fan development. We suggest that, in the future, both ancient and modern deep-sea fans be more closely examined for mass-transport deposits so that the importance of this process to overall fan development can be more accurately assessed.