Glacier Dammed Lakes in Norway

Glacier dammed lakes may have their outflow over a bedrock threshold like other lakes, or they may flow on the surface or below the damming ice. In the former case the lake, over some considerable period, has a constant maximum level with marked shore lines corresponding to the threshold. But when the level is determined by the ice dam, the conditions are unstable. The level of the lake will then to a certain extent vary in step with the glacier, and never remain at a certain level for any length of time. The normal behaviour of such a lake will be a moderately fast rise of the water level, dependent upon the supply, until a certain critical level is reached, whereupon drainage is rapid. Such is also to some extent the case with the type of lake first mentioned, if the height of the pass is situated near to the critical level for drainage.