SGER: Geomorphic Effects of a Jokulhlaup

0413628WohlJokulhlaups 是冰川溃决洪水，在单个冰川存在期间，当冰川冰下有足够的融水池时，可能会反复发生。这些周期性的突发洪水虽然持续时间较短，但其震级和水流功率均高于冰川或雪融化产生的正常季节性高流量。因此，冰峰会对下游地貌特征产生不成比例的巨大影响。许多研究描述了冰岛等高纬度环境中发生的冰峰对水文、水力学和地貌的影响。冰河湖在高海拔环境中也可能具有重要的地貌意义，但尚无研究检验冰河湖在山区的地貌影响。拟议研究的主要目的是检查怀俄明州风河山脉最近的冰河湖的流动路径，以验证这样的想法：在一些高海拔河道中，冰河湖提供的流量主要塑造河道和谷底的几何形状。2003年9月上旬，怀俄明州风河山脉的草蜢冰川顶部的冰堰湖爆发了冰河湖。 12 公顷的湖泊估计将 320 万立方米的水排泄到冰川下方的斜坡上，并沿着支流山谷流入风河谷。距冰坝湖下游约 33 公里处的美国地质调查局 (USGS) 测厚仪记录了这次溃决洪水。我们将检查 jokulhlaup 沿线的 5 个地点。在每个地点，我们将 (i) 调查洪水前和洪水后河道的几何形状以及 jokulhlaup 的高水位线，(ii) 调查大型沉积特征，以计算沉积量，并将大量沉积的位置与山谷梯度和几何形状联系起来，这将使用地形图来表征，(iii) 调查存在这些特征的大型侵蚀特征，并将其位置与山谷梯度和几何形状联系起来，以及 (iv) 计算正常季节性峰值流量和河流的流量和水流功率。冰河湖。利用这些现场数据和计算，我们期望创建一张 jokulhlaup 侵蚀和沉积特征的地图，并定量地将这些特征的位置与山谷几何形状和 jokulhlaup 溪流功率的变化联系起来。我们还将计算 jokulhlaup 水流功率与沿 jokulhlaup 长度的正常季节性峰值流量水流功率之比。这些数据将使我们能够定量推断 2003 年 9 月的 jokulhlaup 相对于 Grasshopper 和 Dinwoody 小溪正常季节性高流量的地貌效果。世界范围内冰川的快速退缩是有据可查的。风河山脉的卫星图像显示，自 1986 年以来，经济衰退尤为严重。风河山脉在这方面并不是独一无二的，美国和世界各地高海拔地区的变暖很可能会引发越来越频繁的冰峰。为了有效地解决与这些冰峰相关的危害和地貌效应，需要对这里提出的类型进行详细和定量的地貌特征描述。 PI 直到 2003 年 12 月才得知 2003 年 9 月的冰峰的存在。在随后的河流流量改变这些特征之前，需要尽快描述冰峰相关的侵蚀和沉积特征，这使得在 NSF 资助的正常周期内提出和开展这项研究变得尴尬。因此，我们正在寻求 SGER 拨款，以快速应对此次 jokulhlaup 事件带来的独特机会。

0413628WohlJokulhlaups are glacial outburst floods that occur may occur repeatedly during the existence of an individual glacier when sufficient meltwater ponds beneath glacial ice. These periodic outburst floods, although of short duration, are of higher magnitude and stream power than normal, seasonal high flows generated by glacial- or snow-melt. As a result, jokulhlaups can exert a disproportionately large influence on downstream geomorphic features. Numerous studies have described the hydrology, hydraulics, and geomorphic effects of jokulhlaups occurring in high-latitude environments such as Iceland. Jokulhlaups are also likely to be geomorphically significant in high-altitude environments, but no studies have examined the geomorphic effects of jokulhlaups in mountainous regions. The primary objective of the proposed research is to examine the flow path of a recent jokulhlaup in Wyoming's Wind River Mountains in order to test the idea that, in some high-altitude stream channels, jokulhlaups supply the discharge that predominantly shapes channel and valley-bottom geometry.A jokulhlaup burst from an ice-dammed lake at the head of Grasshopper Glacier in Wyoming's Wind River Mountains during early September 2003. The 12 ha lake drained an estimated 3.2 million m3 of water downslope, underneath the glacier, and down tributary valleys into the Wind River valley. The outburst flood was recorded at a USGS gage approximately 33 km downstream from the ice-dammed lake. We will examine 5 sites along the path of the jokulhlaup. At each of these sites we will (i) survey pre- and post-flood channel geometry and high-water marks from the jokulhlaup, (ii) survey large depositional features in order to calculate volume of deposition, and to relate locations of substantial deposition to valley gradient and geometry, which will be characterized using topographic maps, (iii) survey large erosional features, where these are present, and relate their locations to valley gradient and geometry, and (iv) calculate discharge and stream power of normal seasonal peak flows and of the jokulhlaup. Using these field data and calculations, we expect to create a map of jokulhlaup erosional and depositional features, and to quantitatively relate the location of these features to variations in valley geometry and jokulhlaup stream power. We will also calculate the ratio of jokulhlaup stream power to normal seasonal peak flow stream power along the length of the jokulhlaup. These data will allow us to quantitatively infer the geomorphic effectiveness of the September 2003 jokulhlaup relative to normal seasonal high flows in Grasshopper and Dinwoody creeks.The rapid recession of glaciers worldwide is well documented. Satellite images of the Wind River Mountains show particularly dramatic recession since 1986. The Wind River Mountains are not unique in this respect, and it is likely that warming at high elevations throughout the U.S. and the world will trigger increasingly frequent jokulhlaups. Detailed and quantitative geomorphic characterizations of the type proposed here are needed in order to effectively address the hazards and geomorphic effects associated with these jokulhlaups. The PI only learned of the existence of the September 2003 jokulhlaup in December 2003. The need to characterize jokulhlaup-related erosional and depositional features as soon as possible, before subsequent river discharges modify these features, makes proposing and conducting this research awkward within the normal cycle of NSF funding. Hence, we are seeking an SGER grant to respond quickly to the unique opportunity presented by the occurrence of this jokulhlaup.