Yardang Geometries And Control Factors In The Qaidam Basin Based On Multi-Source Remote Sensing Images

Yardangs are typical erosional landforms,and mostly occurred in hyperarid and semiarid desert and surrounding areas except Australia,and Antarctica.The Qaidam basin developed the most widely yardang in different shapes,which provide a guarantee for the quantificationally extraction of large data,and analyze yardang geometries and control factors.It is difficult to obtain comprehensive data by conventional geological survey because of the remote location and the bad weather of the Qaidam basin.Thus,this paper mainly discussed the geometries,the relationships among the yardang development,geologic structures and wind regime,manifest oscillatory wind regimes fluctuations based on the cross-cutting relationships of yardangs,and explore the relationship between the denudation quantity in the QaidamBasin and sand accumulation in the Loess Plateau through estimating denudation quantity and erosion rate,based on multisource remote sensing images provided by Google EarthTM,Landsat 8multispectral image,Unmanned aerial vehicle(UAV),Digital Elevation Model(DEM),geologic map and topographic map.The main content and conclusions are following:(1)Based on multisource remote sensing images,we extracted the geometries of 16749 yardangs,such as length-width ratio(L/W),orientation,density,and spacing.The orientation dominated N-NW strike and showed subparallel arrangement in the basin.The length ranges from 3.5 m to 4803 m with the mean value 106 m.The width ranges from 1.5 m to 309 m with the mean value 24 m.The L/W ranges from 207:1 to 1.03:1 with the mean value 3.8:1.(2)Yardangs were classified into four types based on their L/W:short-axis(1:1-2:1),whale-back(2:1-6:1),hogback(6:1-10:1)and long-ridge(10:1-210:1).For the short-axis yardangs,their lengths range from 3.5 m to 182 m,widths range from 2.4 m to 114 m,For the whale-back yardangs,lengths range from 3.8 m to 1159 m,widths range from 1.5 m to 309 m.For the hogback yardangs,lengths range from 13 m to 2013 m,widths range from 2 m to 264 m.The long-ridge yardangs have lengths that range from 57 m to 4803 m,widths that range from 5.4 m to 171 m.(3)Nearly 69%of the yardangs with long-ridge and hogback geometries are distributed in syncline areas whereas 73%of the yardangs with short-axis geometries are distributed in anticline areas;and the L/W of yardangs exposed along the windward limbs of anticlines is lower than that of yardangs exposed along the leeward limbs.The results show that the yardang geometries are mainly controlled by the structural geology,the interbedded soft and hard beds,and the angle between geomorphically-effective wind directions and the strike of bedding,(4)In northernmost(Eboliang I independent natural areas)and westernmost(Changweiliang to Jianshishan area)parts of the Qaidam basin where there are locally two geomorphically-effective wind directions,yardangs are sculpted by two different winds.NNW and NNE winds vector superposed in northernmost parts and eroded yardangs in the same time,influencing the orientation of yardangs;NW and NNE winds eroded yardangs alternately,and sculpted yardangs into mounds and exhibit cross-cutting relationships,influencing the L/W of yardangs.These cross-cutting relationships of yardangs reflect the small scale oscillatory wind regimes in the past.(5)Using the ridge line to estimate the denudation quantity and erosion rate are calculated as the minimum reference value,only one-tenth of the results calculated using stratigraphic contrast.The average erosion rate of Qaidam Basin is 0.22 mm/yr,and the corresponding total denudation quantity is 2.2×104 km3.