The Richat Structure is not a structure in the usual sense.
It is a natural feature located in the Sahara Desert of
Mauritania. It is unusual because it is nearly circular.
It was href="http://www.eorc.nasda.go.jp/en/imgdata/topics/2003/tp031015.html">first
observed from space, in 1965, by the astronauts James A.
McDivitt and Edward H. White. (Irrelevant comment: both
McDivitt and White attended the University of Michigan, and there is a href="http://www.flickr.com/search/?q=mcdivitt&w=27345247%40N00">plaza,
near the diag, named for them.)
Richat Structure was thought to have been formed by a meteor
impact. Upon further review, it was found to not have the
features of such an impact. Consequently, it now is thought
to be a circular anticline. It consists of Paleozoic
quartzites. Erosion removed the sand, but the quartzite is much more
resistant to erosion.
As depicted on Nasa’s Earth Observatory site:
This true-color scene was acquired by the
Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard
NASA’s Terra satellite, on March 11, 2002.
This is the sort of image we are accustomed to seeing. Now
there is one that is more interesting, posted on Wikipedia.
(Below the fold, of course…)
In order to fully appreciate it, you might want to
high resolution version (2259×1244, 495 KB). Part
of the image was taken during the href="http://www2.jpl.nasa.gov/srtm/">Shuttle Radar
Topography Mission, and part is a Landsat image; the two were
combined,as described on the href="http://photojournal.jpl.nasa.gov/catalog/PIA04963">JPL
This view was generated from a Landsat satellite
image draped over an elevation model produced by the Shuttle Radar
Topography Mission (SRTM). The view uses a 6-times vertical
exaggeration to greatly enhance topographic expression. For vertical
scale, note that the height of the mesa ridge in the back center of the
view is about 285 meters (about 935 feet) tall. Colors of the scene
were enhanced by use of a combination of visible and infrared bands,
which helps to differentiate bedrock (browns), sand (yellow, some
white), minor vegetation in drainage channels (green), and salty
sediments (bluish whites). Some shading of the elevation model was
included to further highlight the topographic features.
In other words, the Structure does not really look like the picture. But
it sure is a nice image. I don’t think it is frivolous, even
though it is not a literal depiction of the Structure. It
shows what kinds of things can be done with this kind of imaging, to
enhance the pictures. This can have href="http://en.wikipedia.org/wiki/Remote_Sensing">practical
applications, in addition to making pretty pictures.