SGER: Geomorphic Effects of a Jokulhlaup

WohlJokulhlaps是一种冰川暴发洪水，在单个冰川存在期间，当冰川下有足够的融化池塘时，可能会反复发生洪水。这些周期性爆发的洪水虽然持续时间很短，但比冰川或积雪融化产生的正常季节性高流量具有更高的规模和水流功率。因此，JOKULHLAUP可以对下游地貌特征产生不成比例的巨大影响。许多研究已经描述了发生在冰岛等高纬度环境中的约库勒劳斯的水文、水力学和地貌效应。在高海拔环境中，乔库拉普也可能具有重要的地貌意义，但还没有研究考察乔库拉普在山区的地貌影响。这项拟议研究的主要目标是研究怀俄明州风河山脉最近的一次约库拉普的流动路径，以检验在一些高海拔河流中，约库拉普提供的流量主要塑造了河道和谷底的几何形状。2003年9月初，怀俄明州风河山蝗虫冰川顶部的一个冰堰湖爆发了约库拉普。这个12公顷的湖从冰川下向下排出了约320万立方米的水，并沿着支流山谷流入风河流域。这场暴发的洪水是在冰堰湖下游约33公里处的美国地质勘探局记录的。我们将检查约库拉普小路沿线的5个地点。在每个地点，我们将(I)调查洪灾前后的河道几何形状和约库拉普的高水位线，(Ii)调查大型沉积特征，以计算淤积量，并将大量沉积的位置与山谷坡度和几何形状联系起来，这将使用地形图来描述，(Iii)调查大型侵蚀特征，如果存在这些特征，并将其位置与山谷坡度和地形联系起来，以及(Iv)计算正常季节性峰值流量和约库拉普的流量和水流功率。利用这些现场数据和计算，我们希望创建一张约库拉普侵蚀和沉积特征的地图，并将这些特征的位置与山谷几何形状和约库拉普河流功率的变化定量地联系起来。我们还将计算沿约库拉普长度的约库拉普水流功率与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月的Jokulhlap相对于蝗虫和Dinwoody小溪正常的季节性高流量的地貌效果。世界各地冰川的迅速退缩是有充分记录的。风河山脉的卫星图像显示，自1986年以来，经济衰退尤为戏剧性。在这方面，风河山脉并不是独一无二的，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玩笑。需要详细和定量地描述这里提出的这种类型的地貌特征，以便有效地处理与这些约库拉普有关的灾害和地貌影响。公安党在2003年12月才得知2003年9月约库勒劳普的存在。在随后的河流排放改变这些特征之前，需要尽快表征与约库勒劳普相关的侵蚀和沉积特征，这使得在NSF资金的正常周期内提出和进行这项研究变得尴尬。因此，我们正在寻求SGER赠款，以迅速响应这次约库拉普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.