A Complex History for Linear Dunes on Earth and Application to Titan
1, Clayton Chandler1, John McBride1, Tom Morris1, Karl Arnold1, Ralph Lorenz2, Jason Barnes3, Alex Hayes4
1Brigham Young University, Provo, UT, USA, 2Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA, 3University of Idaho, Moscow, ID, USA, 4Cornell University, Ithaca, NY, USA
Dunes of Saturn’s moon Titan visible at the resolution of Cassini Synthetic Aperture RADAR (SAR) are linear in form and similar in size and shape to the large, high inertia linear dunes of Earth. Gaining a better understanding of the nature of sand transport on Earth’s dunes will inform similar processes on Titan, where energies and materials are vastly different.
A field study of dunes in the Namib Sand Sea was undertaken 13 km south of Gobabeb in August 2013. The dunes here are ~1 km wide and extend N-S for over 20 km. The crestlines are highly sinuous and there are abundant flanking dunes. On the west side of our primary study dune, flanking dunes are regularly spaced and transverse to the crestline. On the east side, the plinth is smaller and steeper and there are more isolated linear flanking dunes with complex crestlines. These landforms are consistent with dominant winds transporting sand from S-N along the west side of the dune, crossing the crestline to extend sands in isolated patterns toward the ENE. These observations are consistent with the presence farther south of auxiliary linear dunes extending eastwards from the primary dune, migrating NNE.
A high-resolution, 200 MHz Ground Penetrating RADAR (GPR) trace perpendicular to the main dune reveals details down to ~10m. Layers at the surface on both sides of the dune are surface parallel, postulated to be from modern mass wasting related to sand movement on the crest. Below this layer on the west are bowl-shaped, truncated layers consistent with the down-dune passage of a large flanking feature, such as a flanking linear dune. On the east at depth are deposits consistent with the presence and passage of large, flanking transverse dunes. These observations of the near-subsurface, with transverse dunes on the east and flanking linear dunes on the west, are opposite to those of the current surface. We suggest the wind conditions that allow for the persistence of these landforms have flipped from what existed in the relatively recent past.
These observations reveal a complicated history for large linear dunes and show that in the Namib, adjustment in major winds may not lead to dramatic changes in shape, whereas shapes have changed elsewhere, such as in the southern Rub al Khali. This also has implications for Titan, which undergoes seasonal, storm-related and likely longer-term, climate-related wind changes, perhaps not always leading to shape change of the dunes.