Subaqueous fan
A subaqueous fan is a fan-shaped deposit formed beneath water (similar to deltas or terrestrial alluvial fans), that is commonly related to glaciers and crater lakes.
Subaqueous fan deposits are generally described as coarse to fine gravel and/or sand, with variable texture and sorting. Underflows (meltwater denser than lake water) tend to produce subaqueous fans with channels and levees. Subaqueous fans can be formed by the influence of glacier movement and by underwater currents typically found at a river delta. The sediment size and composition that makes up the subaqueous fan is dependent on the type of rock that the water flow or glacial ice sheet moves over. Sedimentary structures found in subaqueous fans are heavily dependent on the strength of the water flow.