Remobilisation of a mass of poorly sorted, sedimentrich
mixture from the edge of the shelf or the top of
the slope results in a debris flow, which travels down
the slope and out onto the basin plain. Unlike a debris
flow on land an underwater flow has the opportunity
to mix with water and in doing so it becomes more
dilute and this can lead to a change in the flow
mechanism and a transition to a turbidity current.
The top surface of a submarine debris flow deposit will
typically grade up into finer deposits due to dilution of
the upper part of the flow. Large debris flows of material
are known from the Atlantic off northwest Africa
(Masson et al. 1992) and examples of thick, extensive
debris-flow deposits are also known from the stratigraphic
record (Johns et al. 1981; Pauley 1995).
Debris-flow deposits tens of metres thick and extending
for tens of kilometres are often referred to as
megabeds.