DEM Based Research On The Loess Landform Inheritance In The Loess Plateau Of China

Landform inheritance refers to the inherited relationship of different landform morphologys in a certain area during the evolutionary process. The loess landform inheritance represents the controlling effects of pre-Quaternary paleotopography to the deposition, erosion and accumulation process of loess dusts, which is centered on the study of the inherited relationship from the pre-Quaternary paleotopography to modern loess landform morphology in the Loess Plateau of China. The research of loess landform inheritance plays key role in revealing the Loess Plateau formation machnism, and also has been regarded as a focused study in the loess landform researches. Previous scholars have carried out many loess landform inheritance studies or its related studies, and many significant achievements have been made. For instance, they have preliminary desciptive discussed the controlling effects of Pre-Quaternary terrain on the modern loess landform formation process. However, there are still lack of agreement and even controversial viewponts towards the subject of loess lanform inheritance, such as the formation mechanism, influence degree, spatial difference etc. In particular, because of the limitations of data and methodrology, previous work still belongs to the research stage of qualitative or semi-quantitative analysis based on the field investigation method in severl typical samples. It still lacks effective data and method to reconstruct a regional loess paleotopographical model, it still unable to effectively reveal the deposition process of how loess dusts deposited on the original underlying paloetopography, it still cannot effectively reveals the controlling process of how loess paloetopography influences the modern gully erosion process, it still cannot effectively reveals what kind of spatial and scale differneces the loess landform inheritance has in the evolutionary process. The solving of aforementioned problems would bring a breakthrough in understanding the formation mechanism of loess landform.The digital elevation model (DEM) and DEM based digital terrain analysis provide new idea and method for a quantitative description and analysis of surface morphology under GIS platform. However, Current DEMs are manily used to express the morphology of terrain surface. If a DEM of pre-Quaternary underlying paleotopography could be reconstructed, it could help to construct a dual-layer DEM with the intergration of modern and underlying terrain. With the dual-layer DEM and the application of GIS spatial analysis methods, the aforementioned scientific problems in loess landform inheritance study could be effectively analyzed and solved, and further realized a theory breakthrough and method innovation in the research of loess landform.In this study, the basic concepts, basic features, geographical meanings and influencing factors have been firstly systematic analyzed and discussed. And then, on a basis of multiple data sources incluing high-resolution DEMs, geological maps, drillings and geophysic detecting profiles, DEMs of pre-Quaternary original terrain before the loess deposition process evolved have been resconstructed with three different scales. In addition, a dual-layer terrain model has been constructed with the intergration of modern and underlying terrain. With the dual-layer terrain model, we finally adopted several indicators including elevation frequency, elevation XY scatter diagram, terrain profile, hypsomtric integral, and slope aspect change etc., to analyze the relationship between modern terrain and underlying terrain, and to achieve a new spatial variation understanding of the loess deposition process under the controlling effect of the pre-Quaternary paleotopography. The main research contents and conclusions of this study are listed as following:(1) The study systematic elaborate the conceptual model of loess landform inheritance, and further summarize and analyze the basic features, analytical prerequisites, influencing factors and geographical meanings of the loess landform inheritance.The loess landform inheritance research could be regarded as a idealistic subject to study the loess landform formation process, and could be used to reveal the inner scientific law of loess deposition process.(2) Based on the data combination of geological maps, field investigating drillings and geophysic detecting profiles, the pre-Quaternary paleotopography of loess landform has been reconstructed in multiple scales. The reconstructed results in the macra scale (entire severe soil erosion area in the Loess Plateau, loess hilly landform of SuidDe, loess ridge landform of YanChuan, loess tableland landform of ChunHua) with different interpolation methods show that:the spline function interpolation method appears suitable for the underlying terrain reconstruction of the entire severe soil erosion area and ChunHua loess tableland landform area, wheras different interpolation methods exist limit influence on the underlying terrain reconstruction in the loess hilly and ridge landform areas. For the underlying terrain reconstruction process of mesoscale (along with the ShenMu-MiZhi, SuiDe-YanChuan, TongChuan-HuangLing YanAn-YanShui highway areas) and micro scale (loess hills in BaiJiaYaYao in YuLin, loess hills in YaoJiaWan in SuiDe, loess ridges in HaoJiaQiao in SuiDe, loess ridges in DingZhuang in YanAn, loess tablelands in ZhangJiaWan in TongChuan, loess tablelands in MaJu in TongChuan), the study used the interpolation results interpolated by geological samplings as the modeling underlying terrain, used the high-density drillings, geophysic detecting profiles and EH4 based geological radar detecting results as the true underlying terrain; Through a comparative analysis of modeling and true underlying terrain, the results show that the reconstructed underlying terrain model by interpolation method could gurrantee the accuracy of the pre-Quaternary paleotopography.(3) In general, the reconstructed paleotopography, located in the severe soil erosion area of the Loess Plateau, shows the original terrain existed the characteristics of high in northwest, low in southeast and about 2000m of total height difference; but it still was a relatively peneplain topography with low terrain relief. This characteristic appears sharp constrast compare to the broken modern loess gully-hilly landform with thousands of deep gullies. From the local views, there is a limited terrain relief of paleotopography compared to that of modern terrain; the terrain relief is about 50m, and the elevation of original peaks is almost at the same horizontal plane, indicating the paleotopography of the Loess Plateau is peneplain topography and belongs to the late geomorphological erosion stage.(4) The dual-layer terrain modern, combined by the underlying terrain model and modern terrain model, together with a series of indicates represent by qualitative, quantitative and positionable analysis method, are the fundamation basis of loess landform inheritance research. The proposed analysis methods and indexes, i.e. elevation frequency change, elevation XY scatter diagram, hypsomtric integral, slope aspect change, gradient and concavity of terrain profiles, can perform well in quantitative description of the geomorphological inheritance of loess landforms.(5) The experimental results of all indicators show a significant landform inheritance relationship between modern terrain and underlying paleotopography. From the overall views, modern terrain is more subdued than the relief of the original paleotopography due to the loess deposition process, and the process was dominated by the windward slope deposition pattern, which caused the systemic offset of the geomorphological features between these two terrains. The offset was influenced by the terrain relief of the paleotopography. From the changing views of macro scale to micro scale of the research domain, the loess landform inheritance characteristics, including terrain relief change, terrain correlationship and geomorphological developmental change, exist a significant variation phenonminon according to the spatial and domain scales. During the formation process of modern erosional gullies, most gullies were formed in the low areas of the original paleotopography, which demonstrated the controlling effect of the underlying terrain on the modern gully evolution. But the young gullies less than 100m or lower gullies, such as shallow gullies, tipple ravines and rills, their formation process have weak influence from the underlying terrain.The study is an exploration and practice of geoscientific problem solving based on the national basic geographic data and other related measured data, as well as GIS spatial analysis method. The entire research process makes us deeply realize that the breakthrough of research idea, method and data, can bring innovative understandings about formation mechanism and spatial variation pattern of loess landform in the Loess Plateau.