SGER: Geomorphic Effects of a Jokulhlaup

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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.