Water flow through Mittivakkat Glacier, Ammassalik Island, SE Greenland

Abstract

Geografisk Tidsskrift, Danish Journal of Geography 106(1):25–43, 2006 The seasonal variability of hourly discharge of the Mittivakkat Glacier, SE Greenland was analyzed at the beginning and the end of the ablation period (May 2005 and August 2004). Spatial and temporal variations in the drainage system, water flow velocity, and travel time through the different media: snow, firn, and glacier ice were estimated. The glacier runoff hydrograph was calculated using the time-area method (a conceptual model) and the snow distribution was modeled using a physically based snow evolution model (SnowModel). Ink and dye tracer experiments, together with water flow measurements and observations, were conducted during August 2004 and May 2005 to estimate flow velocities through snow, firn, and glacier ice. The Mittivakkat Glacier contained five different water flow paths through the different media of the partially snow-covered glacier in August 2004, and three paths when the glacier was fully snow-covered in May 2005. In both August 2004 and May 2005, flow experiments revealed velocities ranging from 1.5× 10−4 to 4.3× 10−4 m s−1 through the snow cover, 3.5× 10−4 to 9.2× 10−4 m s−1 at the interface between the snow and the impermeable glacier ice, an average of 5.0× 10−2 m s−1 for inter-rill flow, a range from 0.46 to 1.84 m s−1 in supraglacial channels, and a maximum travel time of approximately 21 hours (time of concentration) through the different Mittivakkat Glacier flow paths. A 3 to 4 how and 5 to 7 hour lag time occurred in August and May, respectively. On a daily basis, the hourly surface melt exceeded the hourly time- area glacier runoff from 4 a.m. to 3 p.m. in August and May, indicating a temporary englacial melt-water storage. The time-area glacier runoff was compared with stage observed runoff during August indicating a R2-value of 0.85. Daily peak runoff values of the time-area runoff and stage runoff correspond well in duration and variability, with a maximum range of 1.57 m3 s−1 for August.