新构造运动影响下的雅鲁藏布江水系发育和河流地貌特征

雅鲁藏布江(雅江)水系发育和河流地貌演变受新构造运动的强烈影响。通过野外调查,结合SRTM(航天飞机雷达地形测绘使命)数据分析和Google Earth三维地图功能,对雅江河网形态及河流地貌特征进行了分析,并采用EH4电磁成像系统测量了雅江及其支流宽谷河道淤沙深度。研究发现,雅江河网呈现格状水系特点,同时具有枝状河网的拓扑性质,这主要是由于新构造运动的影响,河网发育过程中受到南北向挤压和东西向拉伸所至。青藏高原阶段性不均匀抬升形成了宽窄相间的藕节状河道形态,宽阔河段河道为辫状河型,而窄深河段为深切的V型河谷、单一顺直河型,纵剖面上构成裂点。裂点河段地块相对上升较快,阻滞了水流和泥沙,上游河段大量卵石和泥沙在河谷里淤积深达800多米,形成了平整而宽阔的U型河谷。整个雅江宽谷段泥沙淤积量约0.9万亿m³。

Drainage network and fluvial morphology features of Yarlung Tsangpo River under the impact of neotectonic movement

The neotectonic activity can have a profound influence on the development of drainage networks and the morphological evolution of fluvial systems in the Yarlung Tsangpo River on the Qinghai-Tibet plateau.Combining field surveys with a Digital Elevation Model(DEM) and the Google Earth 3D map technology,the drainage network pattern and the fluvial morphology of the Yarlung Tsangpo basin are analyzed in this study.The fluvial deposits of the main channel and tributaries in the basin are measured using the EH4 electromagnetic imaging system.The results show that the drainage network in the Yarlung Tsangpo River exhibits a trellis-dendritic drainage pattern.This is mainly due to the north-south contraction and the east-west trending extension in the plateau resulting from the neotectonic activity.The alternating wide and narrow fluvial landscapes could be the result of the uneven uplift of the Qinghai-Tibet Plateau.The braided and anastomosing rivers are usually found in wide river valleys.While a single,entrenched,relatively straight channel often develops in the narrow V-style valley,and many knickpoints occur along the longitudinal profile of rivers.The mechanism behind the knickpoint development is that the fluvial deposits of narrow channels increase at a faster rate than that of wide channels.The presence of knickpoints will lead to enhanced overall sedimentation rates,which forms a wide U-style valley with a deposition depth of over 800 meters.It is estimated that the total amount of sediment deposited on the Yarlung Tsangpo basin on an the order of magnitude of 0.9 trillion cubic meters.