Summary

After centuries of geological controversy it is now well established that the last major deglaciation of planet Earth involved huge fluxes of water from the wasting continental ice sheets, and that much of this water was delivered as floods of immense magnitude and relatively short duration. These late Quaternary megafloods, and the megafloods of earlier glaciations, had short-term peak flows, comparable in discharge to the more prolonged fluxes of ocean currents. (The discharges for both ocean currents and megafloods generally exceed one million cubic metres per second, hence the prefix ‘mega’.) Some outburst floods likely induced very rapid, short-term effects on Quaternary climates. The late Quaternary megafloods also greatly altered drainage evolution and the planetary patterns of water and sediment movement to the oceans. The recent discoveries of Mars missions have now documented the importance of megafloods to the geological evolution of that planet. As on Earth, the Martian megafloods seem to have influenced climate change.

Introduction

Up until the middle nineteenth century considerable progress was being made in scientific studies of the role of catastrophic flooding in the geological evolution of river valleys. While some of these studies invoked a kind of biblical catastrophism, much of the work merely employed hypotheses of immense floods because these inferences seemed to provide the best explanations for such features as scoured bedrock and accumulations of huge, water-transported boulders.