FORMATION OF LINEAR DUNES AND IMPLICATIONS FOR PLANETARY SURFACE PROCESSES

Linear dunes are the only dune forms that has been found on all the terrestrial planets and moons that have an atmosphere, including the Earth, Mars, Venus and Saturn’s moon, Titan. Linear dunes represent 40% of all dunes found on our planet, and they cover nearly half of the Australian continent. What is so enigmatic about these features is that despite how common they are scientists are still not sure how they form. The problem is that linear dunes are often enormous features that can be tens of meters high and wide while stretching over hundreds of kilometers in length, thus making it hard to study any one particular dune or dune field. Currently, there are three competing hypotheses for their formation. The linear extension hypothesis suggests that they originate from a single source of sand far removed from the dune field and the dunes grow forward over great distances. Wind-rift hypotheses suggest that the sand is derived locally, and the dunes grow upward (vertical accretion) or forward (linear extension). The lateral migration hypothesis also suggests that the sand was derived locally and that vertical accretion is important, but some observations suggest that the dunes migrate laterally and coalesced over time.

I will discuss some of the latest observations of linear dunes and the implications these studies have for understanding their formation and development, including our ongoing investigations of linear dunes located in the Simpson Desert [e.g., Craddock et al., 2015, J. Geophys. Res. Planets, 120, 1736–1750, doi:10.1002/2015JE004892]. In general, linear dunes form in environments where there is abundant sand and the wind direction is multimodal. Unlike most dune forms that are a result of sediment transport, linear dunes appear to be nature’s way of storing sediment. Various investigations also indicate that linear dunes development in alternating phases of lateral and vertical growth over time, indicating that linear dunes reflect temporal changes in the climatic environment. The implications such terrestrial studies have for understanding the surface of Mars, Venus, and Titan will be discussed.