SGER: Geomorphic Effects of a Jokulhlaup

[413628] wohljokulhlaups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时，可能会反复发生。这些周期性的溃决洪水虽然持续时间短，但其强度和水流功率都高于冰川或冰雪融化产生的正常的季节性高潮。因此，jokulhlaups可以对下游的地貌特征施加不成比例的巨大影响。许多研究描述了发生在高纬度环境（如冰岛）的jokulhlaups的水文、水力学和地貌影响。Jokulhlaups在高海拔环境中也可能具有重要的地貌意义，但没有研究调查Jokulhlaups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一个冰川的流动路径，以验证在一些高海拔的河流通道中，冰川提供的流量主要决定了通道和山谷底部的几何形状。2003年9月初，怀俄明州风河山脉Grasshopper冰川顶部的冰封湖泊爆发了一次冰川崩裂。这个占地12公顷的湖泊将大约320万立方米的水往下坡、冰川下面和支流山谷流入风河山谷。美国地质勘探局在冰坝湖下游约33公里处记录了溃决洪水。我们将沿着冰川的路径考察5个地点。在这些地点，我们将(i)调查洪水前和洪水后的河道几何形状和jokulhlaup的高水位标志；（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，这些特征将使用地形图进行表征；（iii）调查大型侵蚀特征，如果存在这些特征，并将它们的位置与山谷梯度和几何形状联系起来。(4)计算正常季节高峰流量和冰川流量的流量和水流功率。利用这些野外数据和计算，我们希望绘制出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水流动力的变化联系起来。我们还将计算jokulhlaup水流功率与沿jokulhlaup长度的正常季节性峰值水流功率的比率。这些数据将使我们能够定量地推断2003年9月jokulhlaup相对于Grasshopper和Dinwoody溪的正常季节性高流量的地貌有效性。世界范围内冰川的迅速消退是有据可查的。风河山脉的卫星图像显示，自1986年以来，风河山脉的衰退尤为剧烈。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川崩裂。为了有效地解决与这些jokulhlaups相关的危害和地貌影响，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在2003年12月才得知2003年9月冰川的存在。在随后的河流排放改变这些特征之前，需要尽快表征jokulhlaup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，以迅速响应这次冰川爆发所带来的独特机会。

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.