Jökulhlaup Observed at Greenland Ice Sheet

On 31 August 2007, about 35 kilometers upstream from the town of Kangerlussuaq, in western Greenland, a roughly 0.5-square-kilometer permanently ice-dammed lake on the northern flank of the Russell Glacier—an outlet glacier of the Greenland Ice Sheet—suddenly broke free and drained into the Watson River (Figure 1). A 25-meter drop in the lake water level resulted over an approximately 17-hour period (Figure 3a). A glacial outburst such as this is known by the Icelandic term jokulhlaup, derived from the words jokull (glacier) and hlaup (meaning sprint or burst) [Robert, 2005]. Before 2007, the last known jokulhlaup from this glacier was in July 1987; jokulhlaups at this location occur once every 8–10 years on average. The 2007 jokulhlaup occurred after the most intensive melt season—with the biggest melting area and melt index (defined as the melting area times the number of melting days)— on the Greenland Ice Sheet since the first satellite observations in 1979 [Tedesco, 2007]. The ice dam broke after 4 days with a temperature range of 4.0°–17.0°C, averaging 9.5°C, resulting in glacier ablation, and with a rainfall total of 33 millimeters (Figure 2a).