Subaqueous fan

[2] 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.

[3] 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.

[5]  These sediments are also known as till and it can be composed of variable sized rock fragments ranging from fine grains up to boulders called erratic.

Eventually, the glacier will retreat and leave a large pile of sediment at its furthest advance called the terminal moraine.

[7]  Eventually, when distances reach approximately 1,000 meters away, the grain size becomes finer and cross laminated, fine-grained sands are often found.

As distances approach approximately a few thousand meters away from the glacial ice, graded fine sands and silts are found and eventually, silt-clays.

As you increase the distance from the glacial ice, sediment develops from heavily disorganized gravels into better organized and graded beds.

This area is known for alternating fine and coarse grained layers called varves that are formed by the seasonal freezing of the proglacial lake surface.

[10] Identification of these depositional fans occurred at the bottom of the Southwestern region of the Melas Chasma (an enclosed basin in this canyon).

Features of these subaqueous fans include several elongated lobes consisting of turbidite deposits and dendritic terminations.

[11] These currents are typically short-lived, but are able to distribute great amounts of sediment into the deep ocean (Figure 4) making them a massive contributor to submarine fan formation.

Figure 1: Depositional model of a subaqueous fan depicting the relationship of sediment grain size and depositional distance away from the glacial ice.
Figure 2: Depositional model of a subaqueous fan with emphasis on sedimentary structure and water flow.
Figure 3: The Mississippi River delta includes these underwater alluvial fans which are denoted by the light brown areas on this satellite imagery from the United States Geological Survey (USGS) and the National Aeronautics and Space Association (NASA). [ 9 ]
Figure 4: Demonstrates how debris flow induces turbidity currents which results in turbidite deposits.