11:30 AM - 11:45 AM
[ACG37-10] Meltwater discharge and flooding of the outlet stream of Qaanaaq Glacier, northwestern Greenland
Keywords:Glacier, Greenland, Surface mass balance, Freshwater runoff
Surface mass balance was significantly more negative in 2015 and 2016 as compared to the other years. Glacier wide mass balance was −0.76±0.13 m w.e. in 2014/2015 and -0.28±0.7 m w.e. in 2015/2016. Before the floods, daily mean temperature rose above 5 °C for 5 days in 2015 and above freezing for almost a month in 2016 at SIGMA-B. Such warm conditions caused intensive melting over the entire glacier, resulting in saturation and disappearance of snowpack from the glacier below 950 m a.s.l. In addition to large exposure of ice surface, heavy rainfall (90 mm d−1) occurred on the date of the flood in 2016. we assume that the exposed ice surface helped immediate runoff of a large amount of rainwater. These analyses suggested the loss of snow cover played a key role in the flood events in 2015 and 2016.
We measured discharge from Qaanaaq Glacier from 21 July to 3 August 2017. Stream discharge rapidly increased on 28 July 2017, leading to a peak value of 8.11 m3 s−1. From 21 to 28 July, snowline elevation rose from 500 to 650 m a.s.l. after intensive melting. Runoff measured before the peak discharge accounted for only 60 % of the estimated total glacier melt, indicating the rest of meltwater remained in snowpack on the glacier. These data suggested snowpack was saturated with meltwater, and rapidly released water during the period of rapid melting and upglacier snowline migration. Together with data obtained by similar measurements in 2018, we conclude that saturation and disappearance of snowpack are the key to predict rapid increase in stream discharge and flooding.
Aoki, T., S. Matoba, J. Uetake, N. Takeuchi, and H. Motoyama (2014), Field activities of the “Snow Impurity and Glacial Microbe effects on abrupt warming in the Arctic” (SIGMA) Project in Greenland in 2011-2013, Bull. Glaciol. Res., 32, 3–20.