Summary

Jökulhlaups in Iceland may originate from marginal or subglacial sources of water melted by atmospheric processes, permanent geothermal heat or volcanic eruptions. The release of meltwater from glacial lakes can take place as a result of two different conduit initiation mechanisms and the subsequent drainage from the lake occurs by two different modes. Drainage can begin at pressures lower than the ice overburden in conduits that expand slowly over days or weeks. Alternatively, the lake level may rise until the ice dam is lifted and water discharges rise linearly, peaking in a time interval of several hours to 1–2 days. The linearly rising floods are often associated with large discharges and floods following rapid filling of subglacial lakes during subglacial eruptions or dumping of one marginal lake into another. Jökulhlaups during eruptions in steep ice and snow-covered stratovolcanoes are swift and dangerous and may become lahars and debris-laden floods. The jökuhlaups can be seen as modern analogues of past megafloods on the Earth and their exploration may improve understanding of ice–volcano processes on other planets.

Introduction

The Icelandic word jökulhlaups means glacier-related floods ranging from small bursts to megafloods of enormous landscaping impact. They may originate from marginal or subglacial sources of water melted by atmospheric processes, permanent geothermal heat or volcanic eruptions. They may range from floods consisting almost entirely of water to hyperconcentrated fluid–sediment mixtures and even more destructive gravity-driven mass flow of mostly volcanic materials mixed with water and ice.