风成沙地地形1/10定律的研究与敦煌鸣沙山成因的猜想

 以风成沙地地形的共性—— 同一性作为切入点,探索了风成沙地地形高长比和深长比的变化范围以及它与气流流速结构的关系。通过调查发现,尽管沙积物尺度有大有小,形态繁简差异悬殊,但绝大多数风积地形,尤其在主风向单一地区,它们的高长比Kg存在着明显的变化范围,其界阈Kg≤1/10;而风蚀地形的深长比Ks也有相同的属性,只是Ks≥ -1/10。如果用K代表沙区正负两种风成地形的共同属性,则K=Kg=-Ks,即K≤|±1/10|。研究认为,风成沙地地表形态之所以具有这种共同特征,主要在于气流与沙质地表的相互作用中,地形的高长比同气流垂直分速与其水平纵向分速之比这两个比例之间相互制衡相互顺应的结果。野外试验证明高长比K≤1/10的沙质地表地形阻力最小、最适宜风沙流通过,因而形态比较稳定,且具有自修复功能,并在治沙工程中已经得到验证和广泛应用。因此称这种比例关系为1/10定律。以高长比1/10为界,对于比值远大于1/10的特殊的沙积物地形,我们以敦煌鸣沙山为例,根据外界山体对气流场的影响以及由此而产生的风速结构的变化,提出对鸣沙山成因的猜想。鸣沙山的形成从反面、从更广阔和更深的层次上证明了1/10定律的存在。

Probe into the "one-tenth" Law of Aeolian Sandy Landform and Guess at Causes of Sand-dinging Mountain in Dunhuang

Taking the identity—commonness of aeolian sandy landform, as cut-in point, the authors probe into the landform structure and its relation with airflow velocity. The survey showed that although the sand accumulations are various in size and different in shape, their structure eigenvalue of most depositional landforms especially in single dominant wind direction area\_ratio of height to length (Kg) change within a certain extent, Kg≤1/10; there is same property for erosion landforms, only the ratio of depth to length Ks≥-1/10. Thus, there is K≤|±1/10| if Kg and Ks are represented by common property K. The reason for this common property existed in aeolian sandy landforms mostly lies in the interaction between airflow and sand surface; that is the result of the ratio Kg keeping conformance with the ratio of airflow vertical velocity to horizontal one. Field test proved that the terrain resistance of sandy landforms is the smallest when Kg≤1/10, these landforms are advantageous for blown sand passing through, so the dune shape can keep stability and also can self-reshape. This landform stable structure is called as “one-tenth” law. For the Sand-dinging Mountain in Dunhuang, a special sand accumulation landform with Kg is far more than one-tenth; the authors have guessed the forming cause of sand dinging from aspects of around mountains influencing airflow field and thereout the induced change of wind fraction. The formation of Sand-dinging Mountain in Dunhuang have also proved the existence of “one-tenth” law from the opposites side, more broad and deep levels.