Bengal submarine fan, with or without its eastern lobe, the Nicobar Fan, is the largest submarine fan known. Most of its sediment has been supplied by the Ganges and Brahmaputra rivers, probably since the Early Eocene. The "Swatch-of-No-Ground" submarine canyon connects to one active fan valley system at a time, without apparent bifurcation over its 2500-km length. The upper fan is comprised of a complex of huge channel-levee wedges of abandoned and buried older systems. A reduction of channel size and morphology occurs at the top of the middle fan, where meandering and sheet flow become more important.