HiRISE Science Team wrote:Yardangs Forming Near Gordii Dorsum (ESP_035558_1830) (HiClip)
The purpose of this observation is to determine how these formations, called “yardangs” are forming within a layer of bedrock.
Yardangs are streamlined hills that are carved by wind erosion from bedrock. The rock must be sufficiently erodible for wind to either deflate (pick up) poorly-consolidated pieces or scrape the surface by blowing sand. HiRISE resolution allows us to view yardangs and the component layers more closely, and to get a better understanding of the material.
“Yardang” is a word of Turkish origin, meaning “steep bank.“ When viewed from above, yardangs can look like the hull of a boat.
Nathan Bridges wrote:The Active Dunes of Nili Patera (ESP_035603_1890) (HiClip)
Nili Patera is one of the most active dune fields on Mars. As such, it is continuously monitored with HiRISE, with a new image acquired about every six weeks.
By monitoring the sand dune changes, we can determine how winds vary seasonally and year-to-year. This observation is one of the more recent Nili images (1 March 2014). Compared to an image acquired on 22 November 2012, changes are obvious. The ripples on the dunes have moved, as well some of the dune boundaries, such as the one at upper left. New landslides on the central dune”s lee face are apparent.
Such changes, in just 16 months (and finer scale changes have been seen in just a couple of weeks), demonstrate the effectiveness of wind in modifying the Martian landscape.
Nathan Bridges wrote:Changing Dunes and Ripples in Olympia Undae (ESP_036099_2615) (HiClip)
Olympia Undae is a large field of sand dunes surrounding Mars’ North Polar ice cap. Because of the high latitude of the dunes, they are covered with water and carbon dioxide frost in the winter and are poorly illuminated. They are best viewed in the summer, when features such as ripples on the dunes’ surface can be seen in detail. (Some dunes are probably also covered over by the cap, but we can’t see them directly.)
In this image, we see the dunes in early summer of this year. The dark material is sand that makes up the dunes. Between the dunes, bright bedrock and some lingering patches of frost that have not yet sublimated are visible. Zooming in, we can see small ripples on the dunes’ surface, as well as the bright inter-dune areas. This area has been viewed several times by HiRISE, so we can compare this image to past ones to see if there have been changes.
Here, we compare the new view to one from approximately a Mars years ago (about 2 Earth years), but slightly later in the summer. The most obvious difference between the images is simply the illumination, with the better lighting in the 2012 image showing finer details. Despite these differences, changes in the boundaries of sand and ripple positions are obvious. This shows that winds, perhaps assisted by the sublimation of frost that may loosen sand, are modifying Olympia Undae year-to-year.
Veronica Bray wrote:Sunken and Pitted Ejecta (ESP_036182_2230) (HiClip)
The objective of this observation was to examine the edge of impact ejecta from a crater to the north-west of this area (north is up, west is to the left). The ejecta visible in the top left of this image seems to be lower than the surrounding surface.
This is unusual because impact ejecta is laid down on top of existing ground. The ejecta also seems to have pits. Perhaps the hot ejecta fell on frozen ground and melted the underlying ice?
Credit: NASA/JPL/University of Arizona
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