海南乐东陆架海底沙波形态特征及活动性研究

RESEARCH ON THE SHAPE CHARACTER AND ACTIVITY OF SUBMARINE SAND WAVES OFF LEDONG,HAINAN ISLAND

利用旁扫声呐、浅地层剖面、测深以及钻探等资料分析了海南岛乐东陆架区海底沙波的形态特征、底质及地层结构;分常态和台风作用两种环境条件。计算了沙波的移动速率.并与海南岛东方陆架区沙波特征进行了对比分析.研究表明:乐东陆架沙波以大型沙丘和小型沙波为主。其剖面都极不对称.沙丘多为新月形,波长多为50～100m,波高多为1～3m,对称系数在6～12之间;小型沙歧脊残多置直线型,波高多在0.1～0.5m之间.研究区沙波活动性较强,常态下迁移速率与东方沙波区西区相同,每年0.06～2m;在台风影响下,沙丘表面活动砂层的移动性增强,在活动砂体迁移的部位则可能出现冲蚀凹坑或沟槽;中小型沙波移动速率骤增,最大可达7～11m/h。

In this paper, various features of submarine sand waves off Ledong, Hainan Island （16m to 24m water depth） are described, and these features include the sand wave shape, bottom matter, and the profile structure. The transfer velocity of sand waves are calculated in the usual and typhoon state and the analogue about the sand wave activities between the Ledong and Dongfang with similar developmental environments was made. It is indicated that most sand dunes and sediment ripples distribute off Ledong. The figure of sand dunes is crescent. Most of the wave height is 1m-3m and length is 50m-100m, and the symmetry index （the ratio of gentle slope to steep slope） is 6-12. In a word, the cross-section is extremely asymmetrical. The wave height of the ripples is 0.1m-0.5m, whose crest line is straight. The activity of the sand waves is intensive in study area. The migration rate of sand wave is 0.06m/a-0.2m/a in the usual state, which is similar to the western area of Dongfang. When typhoon influences the study area, the activity of the loose sand which spread in the sand dunes will be more and more intensive. The erosion rut and trough can be found in the place where the loose sand has transferred. The migration rates of the little and medial sand waves will be 7m/h-11m/h at the highest in typhoon state.