Submarine landsliding and canyon evolution on the northern KwaZulu-Natal continental shelf, South Africa, SW Indian Ocean
Submarine landsliding and canyon evolution on the northern KwaZulu-Natal continental shelf, South Africa, SW Indian Ocean
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印度洋西南部夸祖鲁-纳塔尔大陆架北部的海底滑坡和峡谷演化
DOI：
10.1016/j.margeo.2008.06.001
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发表时间：
2008
期刊：
影响因子：
2.9
通讯作者：
R. Uken
中科院分区：
文献类型：
--
作者：
A. Green;R. Uken
在南非北方夸祖鲁-纳塔尔大陆架的几个不同大小和形态的海底峡谷内发现的滑坡的形态和地貌分析，提供了对海底峡谷演变的深入了解。六个大的大陆架锯齿状峡谷（Leven，North和South Leadsman，Diepgat，Wright和白色沙滩）被识别出来，其中穿插着最北端Mabibi地区突出的较小峡谷。滑坡及其表面属性是由高分辨率多波束测深数据确定的。滑坡面积、体积、出口长度、出口坡度、头崖坡度和高度、坡坎坡度、相邻局部未破坏坡度和每个破坏深度均进行测量，并对每个海底峡谷的关系进行统计分析。滑坡的位置和类型也被记录下来。头坎高度与跳动长度（D/L）之间的比率被假定为每个故障的动态流变学的一个很好的代理。最大的失效发生在Diepgat、Wright、Leven和Leadsman的双头阀中。更陡峭和更大的故障头陡坎的存在表明，故障流变学是称职的Diepgat和赖特的龙头，而故障，特别是在头部的Leven和Leadsman龙头被认为具有fluoresced流变学的基础上，其小D/L值。分别假设Diepgat/Wright和Leven/Leadsman滑坡集为滑坡与流体侵蚀触发。最小的滑坡发生在马比比地区，仅限于每个小峡谷顶部的单个后退式滑坡。这种类型的失败也是明显的，在其他较小的峡谷之间发生的较大的货架缩进品种。在峡谷深泓线相对于其壁变得过陡之前，假定发生了由小的后退破坏引起的溯源侵蚀。一旦过陡，横向峡谷扩展可能发生，加上增加下坡侵蚀泥沙流。存在1）下切的内峡谷; 2）峡谷端壁中悬挂或栖息的滑坡; 3）阶梯状滑坡;以及4）滑坡材料中的台阶，表明在海底峡谷演化的这一阶段，轴向切口和灾难性的边坡间隙非常突出。海平面缺口内故障陡坎的存在表明，峡谷目前是不活跃的，不太可能进一步扩大，等待相对海平面下降在下一个低温（冰川）时期。
The morphometric and geomorphological analysis of landslides found within several submarine canyons of varying sizes and morphologies from the northern KwaZulu-Natal continental shelf, South Africa, provides insight into submarine canyon evolution. Six large shelf indenting canyons are recognised (Leven, North and South Leadsman, Diepgat, Wright, and White Sands) interspersed with smaller canyons that occur prominently in the northernmost Mabibi area. Landslides and their surficial attributes were determined from high resolution multibeam bathymetry data. Landslide area, volume, runout length, the slope of the runout, the headscarp slope and height, scar slope, adjacent local unfailed slope gradient, and the depth of each failure are measured and the relationships statistically analysed for each individual submarine canyon. Landslide position and the type of landslide are also documented. The ratio between headscarp height to runout length (D/L) is assumed as a good proxy for the dynamic rheology of each failure. The largest failures occur in Diepgat, Wright, Leven and Leadsman Canyons. The presence of steeper and larger failure headscarps indicates that the failure rheology was competent in Diepgat and Wright Canyons, whereas failures, particularly in the heads of Leven and Leadsman Canyons are assumed to possess fluidised rheologies based on their small D/L values. A landslide vs. a fluid sapping trigger is postulated for the Diepgat/Wright and Leven/Leadsman landslide sets respectively. The smallest landslides are found in the Mabibi area, and are limited to single retrogressive slumps in the heads of each small canyon. This style of failure is also evident in other smaller canyons that occur between the larger shelf indenting varieties. Headward erosion by small retrogressive failure is assumed to occur, before the canyon thalwegs become oversteepened relative to their walls. Once oversteepened, lateral canyon extension may occur, coupled with increased downslope erosion by sediment flow. The presence of 1) incised inner gorges; 2) hanging or perched slides in the canyon headwalls; 3) terraced slides; and 4) benches in the slide material indicate that axial incision and catastrophic slope clearances during this phase of submarine canyon evolution were prominent. The presence of sea-level notches within the failure scarps indicates that canyons are currently inactive and are unlikely to enlarge further pending relative sea-level fall during the next hypothermal (glacial) period.