SGER: Geomorphic Effects of a Jokulhlaup

0413628 WohlJokulhlaups是冰川爆发洪水，可能会在个别冰川存在期间反复发生，当足够的融水池塘在冰川冰下时。这些周期性爆发的洪水虽然持续时间短，但其规模和水流动力都高于冰川或积雪融化产生的正常季节性高流量。因此，jokulhlaups可以对下游地貌特征产生不成比例的巨大影响。许多研究描述了在高纬度环境（如冰岛）中发生的jokulhlaups的水文学，水力学和地貌影响。Jokulhlaups也可能在高海拔环境中具有重要的地貌意义，但没有研究研究过Jokulhlaups在山区的地貌影响。拟议研究的主要目标是检查最近的jokulhlaup在怀俄明州的风河山脉的流动路径，以测试的想法，在一些高海拔的河流渠道，jokulhlaup供应的流量，主要形状渠道和谷底的几何形状。一jokulhlaup从冰坝湖在头的蚱蜢冰川在怀俄明州的风河山脉在2003年9月初爆发。这座12公顷的湖泊沿着山坡、冰川下方、支流山谷流入风河山谷，估计排水量为320万立方米。在冰坝湖下游约33公里处的美国地质勘探局水位计记录到了突发洪水。我们将检查5个地点沿着的道路jokulhlaup。在每个地点，我们将（i）调查jokulhlaup洪水前和洪水后的河道几何形状和高水位标志，（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坡度和几何形状联系起来，将使用地形图对其进行表征，（iii）调查存在的大型侵蚀特征，并将它们的位置与山谷坡度和几何形状联系起来，以及（iv）计算正常季节性洪峰流量和jokulhlaup的流量和水流功率。使用这些现场数据和计算，我们希望创建一个地图jokulhlaup侵蚀和沉积特征，并定量地将这些特征的位置与山谷几何形状和jokulhlaup流功率的变化。我们还将计算jokulhlaup流功率与正常季节性峰值流量流功率沿着jokulhlaup长度的比率。这些数据将使我们能够定量地推断2003年9月的jokulhlaup相对于正常的季节性高流量在蚱蜢和Dinwoody creeks的地貌有效性。全球冰川的快速衰退是有据可查的。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jokulhlaups。为了有效地解决与这些jokulhlaups相关的危害和地貌影响，需要详细和定量的地貌特征。PI在2003年12月才得知2003年9月jokulhlaup的存在。需要尽快表征jokulhlaup相关的侵蚀和沉积特征，随后的河流排放修改这些功能之前，提出并进行这项研究在NSF资助的正常周期内尴尬。因此，我们正在寻求一个SGER赠款，以迅速响应这个jokulhlaup的发生所带来的独特机会。

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.