黄土高原侵蚀环境与侵蚀速率的初步研究

黄土高原的侵蚀是一个地质过程.晚更新世以前高原已经过三个大的侵蚀堆积旋迥,主要沟谷系统和黄土地貌的塬梁峁格局已经形成.全新世以来黄土的堆积逐渐减缓,而侵蚀则进入新的发展时期.在自然因素和人类活动的共同作用下,土壤侵蚀加剧.根据侵蚀一堆积相关原理,利用黄河下游不同时期发育的冲积扇沉积模式,估算了全新世以来自然侵蚀速牵为7.9%,由于人类活动而引起的加速侵蚀的速率逐渐递增,至今已达到25%.

PRELIMINARY STUDY OF THE EROSION ENVIRONMENT AND RATES ON THE LOESS PLATEAU

The present Loess Plateau dissected by the intercrossed gullies is a result of the strong erosion in the long period, which were determined by the climatic and geologic conditions. With the strongly uplifting of Qinghai-Xizang Plateau and the strengthening of East Asian monsoon since Quaternary, the climate of the Loess Plateau has been significantly differentiated in the longitudinal and latitudinal directions. The animal fossils and spore pollens reflect the characteristics of arid climate and it became drier and drier from the early Pleistocene to the late Pleistocene.Since the end of Pliocene, the intermittent uplifting of neotectonic movements and the descending of the depressions and basins on the boundary of the Loess Plateau have gradually increased the topographic gradient. Take Suide-Wubao area as an example, the gradient about 2.8% in the early Pleistocene had been increased up to 8.5% in the late Pleistocene. The erosion and deposition processes of the Loess Plateau were originated and developed in these climatic and geologic environments.By the end of the late Pleistocene, the Plateau had experienced three principal cycles of erosions and depositions, and the main gullies and loess geomorphology had been formed.Since the Holocene, the accumulation has been finished, while the developing stage of erosion has been starting. From the principle of relative accumulation, the rates of natural and accelerated erosion are deduced with the alluvial fans in different stages in the lower reaches of Huanghe. Before Tang Dynasty, the soil erosion of the Loess Plateau was only the natural process, and the accelerated rate of natural erosion was about 7.9%; since Tang Dynasty, human activities have been stimulating the acceierated erosion. The present rate of accelerated erosion caused by the human activities has been increased up to 25%.The regional differences of modern erosion on the Loess Plateau is the historical succesion and development.