Wood-mediated geomorphic effects of a jökulhlaup in the Wind River Mountains, Wyoming
Wood-mediated geomorphic effects of a jökulhlaup in the Wind River Mountains, Wyoming
复制标题
怀俄明州风河山脉冰川冰川的木材介导的地貌效应
DOI：
10.1016/j.geomorph.2008.02.002
复制
发表时间：
2008
期刊：
影响因子：
3.9
通讯作者：
E. Wohl
中科院分区：
文献类型：
--
作者：
E. B. Oswald;E. Wohl
2003年9月初，一个jökulhlaup从怀俄明州风河山脉的蚱蜢冰川顶部爆发。沿着丁伍迪河流域划分了五个具有不同沉积模式的河段。本文重点介绍了jökulhlaup路线的一部分，在那里，森林河岸的侵蚀造成了16个纵向间隔数十至数百米的大型木塞。主河道上游的淤积在每个堵塞物形成了局部的沉积物楔，堵塞物在jökulhlaup期间促进了漫滩沉积。在2004年和2006年的实地调查记录堵塞的特点和相关的侵蚀和沉积特征，以及在正常的季节性高流量通道内的堵塞和洪水沉积物的初始修改。自2003年以来，溢岸存款没有受到流动的影响。实地测量支持三个假设，即（i）jökulhlaup路线沿着的森林部分的堵塞比邻近的、最近没有经历过jökulhlaup的类似河流通道的堵塞更大，间隔更近;（ii）jökulhlaup路线沿着的堵塞不是随机分布的，而是反映了通道和山谷几何形状以及洪水水力学的特定条件;以及（iii）堵塞物的存在促进了显著的侵蚀和沉积效应。本文记录了一系列事件，其中突发洪水增强银行侵蚀和招聘的木材进入渠道，从而形成大的堵塞。这些淤塞足以使水流偏转，在正常融雪峰值流量不常到达的谷底区域产生大量漫滩沉积，并通过这一过程促进谷底加积和沉积物储存。因此，冰川溃决洪水发生的变化有可能改变这些环境中谷底动态的速度和规模，鉴于对全球变暖和冰川退缩的预测，这一点特别重要。在这个现场观察到的过程可能发生在其他森林集水区与河源冰川。
A jökulhlaup burst from the head of Grasshopper Glacier in Wyoming's Wind River Mountains during early September 2003. Five reaches with distinct sedimentation patterns were delineated along the Dinwoody Creek drainage. This paper focuses on a portion of the jökulhlaup route where erosion of the forested banks created 16 large logjams spaced at longitudinal intervals of tens to hundreds of meters. Aggradation within the main channel upstream from each logjam created local sediment wedges, and the jams facilitated overbank deposition during the jökulhlaup. Field surveys during 2004 and 2006 documented logjam characteristics and associated erosional and depositional features, as well as initial modification of the logjams and flood deposits within the normal seasonal high-flow channel. Overbank deposits have not been altered by flows occurring since 2003. Field measurements supported three hypotheses that (i) logjams present along the forested portions of the jökulhlaup route are larger and more closely spaced than those along adjacent, otherwise comparable stream channels that have not recently experienced a jökulhlaup; (ii) logjams are not randomly located along the jökulhlaup route, but instead reflect specific conditions of channel and valley geometry and flood hydraulics; and (iii) the presence of logjams facilitated significant erosional and depositional effects. This paper documents a sequence of events in which outburst floodwaters enhance bank erosion and recruitment of wood into the channel, and thus the formation of large logjams. These logjams sufficiently deflect flow to create substantial overbank deposition in areas of the valley bottom not commonly accessed by normal snowmelt peak discharges, and through this process promote valley-bottom aggradation and sediment storage. Changes in the occurrence of glacier outburst floods thus have the potential to alter the rate and magnitude of valley-bottom dynamics in these environments, which is particularly relevant given predictions of worldwide global warming and glacial retreat. Processes observed at this field site likely occur in other forested catchments with headwater glaciers.