This mixture is denser than the pure water, and a density current results. Older students might want to consider how density currents could form on other planets, or in stars. For example, on the cold moons of Jupiter, compounds that are gases on Earth can be liquid or solid. In the Sun, density currents caused by temperature differences might form in hot plasma. Even here on Earth there are other kinds of density currents.
Density currents can form in gases too.
The students might like to try using differently colored sediment and creating multiple turbidites in the same tank. The different colors of sediment will allow them to see differences in the patterns of deposition of the turbidites. Most natural turbidites fine upward. This paper is based on a science project by the author and Morgan Kopaska-Merkel, and presented by the latter. Co., New York, p. 335-340.