黄土高原的地理信息系统(GIS)试研究

黄土高原水土流失举世瞩目,现在的侵蚀继承和发展了古代的侵蚀,受自然和社会双重因素制约.随着人类社会进步和历史演进,自然与社会因子影响侵蚀的比例不断发生改变.本文从数字黄土高原的角度研究黄土的分布特征和堆积、侵蚀过程,建立了地貌、地质、黄土剖面、水文等空间数据库,研制数字黄土分布图件,展示黄土分布特点,构建黄土的三维分布模型,模拟主要地质时期黄土分布,探讨了侵蚀过程和人类活动对侵蚀的影响.

PRELIMINARY STUDY ON LOESS PLATEAU WITH GIS

The Loess Plateau, a megageomorphic unit,was also resulted from geological processes. Soil erosion on the Chinese Loess Plateau is known for its seventy in the world. This not only inherited and developed from ancient erosion, but also was controlled by natural and social factors. Although a lot of work has been done for the loess palaeoenvironment and loess erosion, few studies were conducted through computer models for geological periods. In this paper some data involving geomorphology, geology, hydrology and 42 loess sections have been collected to establish the database. With the help of GIS technology and grid data model these data are integrated to draw digital loess map showing up the features of loess distribution and to built three-dimensional loess model simulating loess distribution in major geological periods. According to the three-dimension figure of Malan loess, a lot of geological phenomenon could be seen: 1) the mantle-fashioned deposition; 2) the ancient landforms and drainage system below the Malan loess are revealed, for example, the Luohe River and Jinghe River were formed before Malan period; 3) the consistence in the ancient drainage systems implies that the ancient landform didn't change too much, and tectonic movement was even and simple; 4) several ancient basins resulted from the ancient erosion didn't fully develop; 5) there maybe exist a significant geological event between Malan and Pre-Malan according to the difference of two geomorphic units before and after the event 6) erosion process was obviously existing after the Malan loess deposition, but no spatial pattern changed, probably because the geologic environment was stable and climate did not change big-enough to alter the geologic surrounding after the fifth MIS stage. Time span of every layer is identical in the three-dimension model of the loess distribution. We assume that if there were no any tectonic movement or erosion on the Loess Plateau, it should have been fiat, and that only erosion on the Loess Plateau makes its surface change. Based on these assumptions, the surface undulation rate of a same time period could be used to indicate the erosion intensity. The three-dimension model of loess distribution shows that the extent of erosion on the Loess Plateau during Pliocene, Early Pleistocene, Middle Pleistocene and Late Pleistocene changed from less intense in Pliocene, stronger in Early Pleistocene, weak in Middle Pleistocene, to the strongest in Late Pleistocene. Today the erosion on the Loess Plateau becomes stronger due to the influence of human activities. However, a lot of work remains to be done for a practical simulation of loess erosion for the modern time.