There is a new explanation for this kind of landform on Earth and Mars.2019-01-22 17:30:54 447 ℃
Dune is a wind-blown sandy landform widely distributed in desert areas on the earth, and it is a wind-blown landform formed by wind erosion, transportation and accumulation of sandy land. A large number of dunes of different shapes have also been found on Mars and Titan.
Dunes are fascinating because of their complex and diverse morphology. Among them, dome dunes are more interesting to scientists because of their unique charm. The< p> dome dune is a kind of dune with special shape. They are round in shape, and their plane shapes are similar to circles or ellipses. They are like steamed buns of large and small, lack of fallen sand slopes and irregular spatial distribution of individuals. Such dunes are common on Mars and Titan.
Fig.1A. Dome dunes on the earth (giant dome dunes along the Tarim Desert Highway, located in the north of the Taklimakan Desert, 40 14_N, 83 31_E, with a height of about 100 meters, the sub-map is a sand-map). B. Small dome dunes on Mars (72 degrees 49 N, 26 degrees 22 E). How do sand dunes form and evolve? According to aeolian geomorphologists, the shape of sand dunes is determined by wind conditions and the abundance of sand sources. However, the formation and development mechanism of special dunes such as dome dunes need to be further studied. Recently, the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences first identified the morphological characteristics of dome dunes, revealed their formation process and influencing factors, and filled in the blank of wind-blown sand geomorphology research. The< p> dome dunes occur in the environment of relatively less abundant sand sources and complex wind conditions. Affected by the complexity of wind conditions, dome dunes can evolve from crescent dunes (dunes similar to crescents in shape) (Fig. 2).
Figure 2: Dune morphological characteristics under different wind conditions in numerical simulation. A. Solitary crescent-shaped and dome-shaped dunes. B. Crescent-shaped and dome-shaped dunes developed on non-erodible beds. C. The complexity of wind conditions is expressed by standard deviation of sediment transport rate. From the picture above, we can see that the dome dunes evolved from the crescent dunes. When the more complicated wind blows in all directions, the crescent moon is gradually "filled up" and piled higher and higher, and becomes a steamed dome dune. The direction and intensity of wind will affect the formation process of these steamed buns. In addition, compared with crescent dunes, dome dunes correspond to more intense wind-sand currents on the surface. At the same time, we can also see that the higher the steamed bread is, the slower the steamed bread moves, which is similar to the crescent dune in dynamic process. In stable state, the higher the height is, the slower the steamed bread moves (fig. 3).
Fig.3 Dynamic mechanism of dome dunes. A. The relationship between the morphological characteristics of dome dunes and wind conditions. B. The relationship between velocity and height of dome dunes.
Using the morphological characteristics and moving speed of the dome dune itself, we can inversely calculate the sediment transport in this area.
Although the direction of sand transport in dome dunes is not as single as that in crescent dunes, the amount of sand transport in a certain direction of dome dunes plays an important role in the formation of dome dunes. Therefore, it is possible to estimate the regional sediment transport and the variation of wind conditions directly by measuring the shape, scale and moving speed of the dome dunes in nature. In addition, we can also be applied to the study of Martian and Titan dunes, which lack wind data. The wind data on Mars and Titan are difficult to obtain, but we can see the patterns and changing rules of these dome dunes through remote sensing images, and then invert and calculate the wind and sediment transport characteristics of Mars and Titan based on these data and the previously established model of the relationship between dome dunes and sediment transport.
That is to say, through these large and small "steamed bun" dome dunes, we can calculate what wind blows and how much sand blows in this area.
Our understanding of the landforms of Mars and Titan may be a step further.
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