PERIODIC outbursts of water from glacier-dammed lakes are ofeconomic as well as of scientific interest. This phenomenon, sometimes called j6kulhlaup (a term used in Iceland for a glacial outburst, which may or may not be associated with volcanic activity), entails the suidden release of ice-impounded water. The subsequent flooding may have disastrous consequences, depending on reservoir capacity and the intensity of downvalley occupance. Fortunately, glacier-dammed lakes are usually isolated and not adjacent to valley settlements, but the exceptions are numerous enough to cause serious loss of life and property. The most disastrous outbursts have recently been summarized by Stone' and Morrison.2 Equally important, glacial outbursts exert an influence on stream morphology, by periodically removing and redepositing vast quantities of sediments. In only a few days a large jokulhlaup may alter the form of a flood plain almost beyond recognition. At least eight types of lakes on or in ice or ice-dammed drain periodically. Hutchinson3 includes seven in his classification of lakes: lakes on the surface of glaciers; lakes within glaciers; lakes on ice sheets; lakes in lateral stream valleys dammed by ice in the main valley; lakes in main valleys dammed by ice from lateral valleys; lakes between glacier and valley walls; and lakes