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Ice–water interactions during floods from Grænalón glacier-dammed lake, Iceland

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This paper explores changing ice–water interactions during jökulhlaups from Grænalón, a 5 × 108 m3 subaerial lake dammed by Skeiðarárjökull, Iceland. Unstable drainage of Graenalón since the early 20th century has resulted in 45 jökulhlaups whose hydrologic character has varied enormously. Geomorphic observations and geophysical measurements from the inlet and outlet zones of the subglacial floodwater tract constrained the hydromechanical factors governing ice–water interactions at Grænalón. To date, three distinct drainage regimes have occurred in response to the changing surface elevation of Grænalón. Shifts from one drainage regime to another involved pronounced changes in jökulhlaup magnitude, timing and cyclicity. Present hydraulic conditions for lake drainage differ from the classical view of a pressure-coupled lake draining directly beneath an ice dam. Instead, lowamplitude drawdown occurs at regular, frequent intervals when hydrostatic pressure in a shallow, rock–ice trench enables water to flow beneath a sagging ice barrier. Floodwater exits Skeiðarárjökull in a supercooled state due to rapid hydraulic displacement from an overdeepened subglacial basin.

Document Type: Research Article


Publication date: January 1, 2005

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  • The Annals of Glaciology is a peer-reviewed, thematic journal published 2 to 4 times a year by the International Glaciological Society (IGS). Publication frequency is determined and volume/issue numbers assigned by the IGS Council on a year-to-year basis and with a lead time of 3 to 4 years. The Annals of Glaciology is included in the ISI Science Citation Index from volume 50, number 50 onwards.

    Themes can be on any aspect of the study of snow and ice. Individual members can make a suggestion for a theme for an Annals issue to the Secretary General, who will forward it to the IGS Publications Committee. The IGS Publication Committee will make a recommendation for an individual themed Annals issue, together with a potential Annals Chief Editor for that issue, to IGS Council. The IGS Council will make the decision whether to proceed, taking into account the spread of topics and the overall capacity for publication of pages in Annals.

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