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The satellite images of Google Earth show an interesting feature of some dune fields of the region near Orinoca Canton, close to the Lake Poopo, Bolivia. They are leaving, during their motion, some sedimentary patterns, such as the coastal dunes of Brazil.
Sedimentary Patterns of Moving Sand Dunes in Orinoca district, Bolivia
Amelia Carolina Sparavigna
Department of Applied Science and Technology, Politecnico di Torino, Torino, Italy
Abstract: The satellite images of Google Earth show an interesting feature of some dune fields of the region near Orinoca Canton, close to the Lake Poopo, Bolivia. They are leaving, during their motion, some sedimentary patterns, such as the coastal dunes of Brazil.
Keywords: Dune motion, Sedimentary patterns, Satellite images, Google Earth.
In two previous papers, we have discussed that some sand dunes are existing, which have a peculiarity with respect to the sand dunes of the deserts [1,2]. The peculiarity is the following: during their motion, these dunes are leaving “footprints” behind, footprints which are the sedimentary patterns due to the seasonal processes occurring to them.
Remarkable examples of sedimentary patterns are those of the coastal dunes of Brazil, created under an environment rich of humidity and with heavy rainfall [3-5]. As discussed in , the observed patterns on the soil are formed due to seasonal phenomena. During the wet season, interdune plains are flooded and the soil is reworked by intermittent drainages; during the dry season, the deposits formed by the drainages and interdune lakes become temporary internal sedimentary sources for the system .
Like the dunes of the desert, the coastal dunes can move, as we can easily see from the time series of satellite images. We can use Google Earth for instance, as discussed in [6-9], to observe the motion of the Brazilian coastal dunes [1,2]. In the given references, we have shown and compared the "footprints” these dunes are producing.
Figure 1: Dune fields in Orinoca Canton, Bolivia.
Here, we will give some examples of sedimentary patterns - observed by means of the Google Earth images - produced by sand dunes that are not coastal dunes such as those we can find near the ocean, but are dunes in a quite different environment. These dunes are in the Orinoca district (cantón) (see Figure 1), in the Andamarca Municipality in the Oruro Department, a mining region in southwest Bolivia. The Orinoca District is located at 3,800 m above sea-level, on the western shore of Lake Poopo. This lake was a large saline lake located in a shallow depression in the Altiplano of Bolivia. Let us note that in , it is told that Lake Poopo "was" a lake. "In December 2015, the former lake had completely dried up, leaving only a few marshy areas. … Suggested causes of the current drying include drought due to climate change, as well as diversion of water for mining and agriculture".
Figure 2. One of the dunes fields of Figure 1. Note the “footprints” of the dunes. The image was recorded in 2012.
Figure 3. A detail of another dune fields of the Figure 2. The image was recorded in 2012.
In the Figures 2 and 3 we can see details of two of the dune fields in the map of Figure 1. We can easily observe the sedimentary patterns the dunes are leaving because of seasonal effects. Supposing that each year, the dune is producing a footprint, we could deduce its motion, as in the Figure 4, using the scale in the image. For instance, the dune in the Figure 4 moved of about 14 meters per year.
For the dunes of Orinoca district, Google Earth is giving only images recorded in 2012. Therefore, we have not information on the recent behaviour of the dunes, on the effect of drought on them and on a consequent variation of their migration rates.
Let us conclude stressing the fact that not only the coastal dunes near the oceans can have sedimentary patterns. As we have shown in this paper, also the sand dunes of a quite different environment can have them. The dunes here shown are on the Altiplano, that is the Andean Plateau or Bolivian Plateau. There the climate is cool with a diurnal cycle of temperature which is very wide. However, as told in , the Altiplano has a marked seasonal cycle of rainfall, with the rainy season concentrated between December and March. The rest of the year tends to be very dry, cool, windy and sunny. Then, it happens that during the wet season, the interdune plains can be flooded. During the dry season, these interdune spaces become temporary areas for sedimentary deposits. In this manner, with a mechanism similar to that of the coastal dunes of Brazil, footprints are formed by the dunes on the Bolivian Altiplano.
Figure 4: Using the patterns we can estimate the motion of the dune. In this case, it was of about 14 meters per year.
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Sparavigna, A. (2016). Sedimentary Patterns of Moving Sand Dunes in Orinoca district, Bolivia. PHILICA.COM Article number 614.