Supraglacial Channels Research Articles

Water flow through Mittivakkat Glacier, Ammassalik Island, SE Greenland

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.

Water temperature in englacial and supraglacial channels: Change along the flow and contribution to ice melting on the channel wall

The physics of water temperature change along a glacial water stream and its relation to ice melting rate on the channel walls are examined. The heat balance equation is based on the principles of energy conservation and an empirical relation of heat exchange between ice and flowing water. It is shown that the temperature of water exponentially approaches a nonzero value as flowing along a glacial channel. The channel meandering and noncircular cross-section were also taken into account. Typical values of the equilibrium water temperature are hundredths to a tenth of a degree depending on the channel size and slope, but the temperature can drastically increase when the channel has sediments. We compared our calculations to 1) a series of experiments with an artificial channel in ice and 2) data obtained from measurements at the Caucasus and Patagonia glaciers.

Geometry of englacial water conduits, Austre Brøggerbreen, Svalbard

The internal geometry of three englacial conduits located on Austre Brøggerbreen, Svalbard, was investigated by tracer experiments and by direct exploration. The tracer tests produced short-lived and highly peaked tracer return curves with high through-flow velocities. The direct inspections revealed the entrances to be of two types. Type I consisted of a moulin with an initial 39 m vertical shaft drained by a semicircular and near-horizontal englacial channel trending diagonally across the direction of ice flow, parallel to tectonic structures observed on the ice surface. The type II entrances sloped gently into the ice in the direction of the ice flow, and became englacial by gradual down-cutting of supraglacial meltwater channels into the glacier surface. No traces of tectonic structures were observed in the ice surface that could have initiated the type II entrances. Englacial conduits with gentle slopes were meandering. With increasing slope, a winding waterfall?plunge-pool geometry was developed, the channels being high (>3 m) compared to their width (30?150 cm).

Ablation Cones on Sidujökull, Iceland

The subject of this study is the ephemeral relief of the edge of one of the Vatnajokull outlet glaciers, called Sidujokull, developed in the shape of dirt cones. Special attention has been paid to the distribution of these forms, influenced by the existence of a system of fissures, supraglacial channels and shear planes in the glacier surface, and to the origin of covering material and development of conical forms. Taking into account the main process of ablation and the shape, a suggestion is made to use the term ‘ablation cone’ instead of ‘dirt cone’.