Linear on Earth and Mars - Comparative Research Haim Tsoar Department of Geography and Environmental Development, Ben-Gurion University of the , Beer-Sheva 84105, Israel ([email protected])

1 2 3 There are two types of linear dunes: Veg- a b etated linear dunes (VLDs), and seif dunes. Each of which is formed and elon- gated by a different mechanism. All linear dunes possess one common char- acteristic of elongation that differenti- ates these dunes from transverse and Barchan and a barchan dunes where the whole body of linear in N the dune advances. Polar region VLDs are covered sparsely or densely by lat/lon 84.4 N 26.4 vegetation. Seif dunes are common in W, North toward the driest , where vegetation right/upper right. 200m cannot survive, such as the or Picture is 1.5 km 250m the . A typical characteristic of 250 m wide resolution is the seif dune is the sinuosity of the about 3 m/pixel crest. Sun from lower a. VLDs - Great Sandy , . b. Seif dunes – Namibia. Arrows show the two VLDs may run in parallel for scores of left. M02-00783 kilometers and are known to cover vast Arrow shows the dominant wind direction. dominant winds. Vegetated Linear dunes in Eastern Sinai Desert areas of the and the http://www.msss.com/moc_gallery/ab1_m04/images/M020083.html after removal of vegetation and bio-crusts. Kalahari in South Africa.

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A 16 cm wide wheel track cut into the sur- face of an aeolian mega-ripple at the Mars Exploration Rover, Opportunity site on Meridiani Planum. The arrows point to blocks of broken, crusted sand disrupted by the action of the rover The formation of lee dunes from wheels. The white box obstacles. Note that the obstacles Dynamics of a seif dune formed by two dominant wind directions. in the right inset are barchan dunes that were shows the context of indurated by crusts. Induration of this image. the lee dunes will bring about its Formation of a lee dune in the lee side of an obstacle. elongation.

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Linear dunes on Earth (right) and Mars (left) – Comparison. The terrestrial dunes are stabi- lized by shrubs and crust. The Martian dunes are indurated by crust. a. Linear dunes near: 84.2°N, 37.9°W. Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image MOC2-1046, 30 March 2005. Width: ~3 km. Linear (lee) dunes at Chasma Boreale near the Lee dunes formed at the lee side of shrubs with dense canopy. This north polar ice cap of Mars (83.9 N, 40.5W). lee dune will elongate when another shrub develops on the lee b. Vegetated linear dunes in the . Linear dunes covered by crust at Qaidam Subframe of MGS MOC image E01-00104. dune and so on. Pendi, China.

Conclusions

• Processes of sand dunes formation, migration and elongation on Mars are similar to those on Earth. • We assume that straight linear dunes on Mars are formed as lee dunes that are indurated sometime after • The induration (crusting) of the surface sand is the explanation for the occurrence of dunes of unusual their formation. morphology on Mars. • We assume that VLDs on Earth initiated as linear (lee) dunes formed in the lee side of shrubs. • Two types of linear dunes are known on Earth: Vegetated Linear Dunes (VLDs) and Seif Dunes. • More field and theoretical works on lee dunes are needed to better understand the straight linear dunes on Mars and the VLDs on Earth.